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ACI 437.1R-07

Load Tests of Concrete Structures:Methods, Magnitude, Protocols,

and Acceptance Criteria

Reported by ACI Committee 437

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American Concrete Institute®

Advancing concrete knowledge

Load Tests of Concrete Structures:Methods, Magnitude, Protocols, and Acceptance Criteria

First PrintingMarch 2007

ISBN 978-0-87031-233-5

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Load Tests of Concrete Structures: Methods, Magnitude, Protocols, and Acceptance Criteria

Reported by ACI Committee 437

ACI 437.1R-07

Tarek Alkhrdaji Ashok M. Kakade Javeed Munshi Thomas Rewerts*

Joseph A. Amon* Dov Kaminetzky Thomas E. Nehil† K. Nam Shiu

Nicholas J. Carino Andrew T. Krauklis Renato Parretti Avanti C. Shroff

Paolo Casadei Chuck J. Larosche Brian J. Pashina Jay Thomas

Ufuk Dilek Michael W. Lee Stephen Pessiki Jeffrey A. Travis

John Frauenhoffer* Daniel J. McCarthy* Predrag L. Popovic Fernando V. Ulloa

Zareh B. Gregorian Patrick R. McCormick Guillermo Ramirez* Paul H. Ziehl*

Pawan R. Gupta Matthew A. Mettemeyer*

*Member of subcommittee that prepared this report.†Chair of subcommittee that prepared this report.

Antonio Nanni*

ChairJeffrey S. West

Secretary

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ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in planning,designing, executing, and inspecting construction. Thisdocument is intended for the use of individuals who arecompetent to evaluate the significance and limitations of itscontent and recommendations and who will acceptresponsibility for the application of the material it contains.The American Concrete Institute disclaims any and allresponsibility for the stated principles. The Institute shall notbe liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.

This report provides the recommendations of Committee 437 regardingselection of test load magnitudes, protocol, and acceptance criteria to beused when performing load testing as a means of evaluating safety andserviceability of concrete structural members and systems. The history ofload factors and acceptance criteria as found in the ACI 318 building codeis provided along with a review of other load test practice. Recommendedrevisions to load factors to be used at this time, additions to load testingprotocol, and revisions to acceptance criteria used to evaluate the findingsof load testing are provided.

Keywords: acceptance criteria; cyclic load test; deflection; deterioration;load test factors; load test protocol; monotonic load test; reinforcedconcrete; strength evaluation.

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ACI 437.1R-07 was adopted and published March 2007.Copyright © 2007, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any

means, including the making of copies by any photo process, or by electronic ormechanical device, printed, written, or oral, or recording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors.

CONTENTSChapter 1—Introduction, p. 437.1R-2

1.1—Background1.2—Introduction1.3—Limitations

Chapter 2—Notation and terminology, p. 437.1R-32.1—Notation2.2—Terminology

Chapter 3—History of load test, load factors, and acceptance criteria, p. 437.1R-4

3.1—Scope of historical review3.2—Summary and conclusions

Chapter 4—Load factors, p. 437.1R-54.1—Introduction4.2—Load factors for various components of service load4.3—Load factors for extreme ratios of live load to total

dead load

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437.1R-2 ACI COMMITTEE REPORT

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Chapter 5—Load test protocol, p. 437.1R-105.1—Introduction5.2—Test load configuration5.3—Load application method5.4—Loading procedures5.5—Loading duration5.6—Load testing procedure

Chapter 6—Acceptance criteria, p. 437.1R-136.1—Criteria for 24-hour monotonic load test6.2—Criteria for cyclic load test6.3—Considerations of performance assessment at service

load level6.4—Recommendations for acceptance criteria at test load

magnitude level6.5—Strength reserve beyond load test acceptance criteria

Chapter 7—Summary, p. 437.1R-17

Chapter 8—References, p. 437.1R-178.1—Referenced standards and reports8.2—Cited references

Appendix A—Determination of equivalentpatch load, p. 437.1R-19

A.1—NotationA.2—IntroductionA.3—One-way slab systemA.4—Procedure and preliminary calculationsA.5—Calculations after calibration cycleA.6—Conclusions

Appendix B—History of load test, load factors, and acceptance criteria, p. 437.1R-23

B.1—NotationB.2—Historical load test practice in the United States and

according to ACIB.3—Other historical load test practices

CHAPTER 1—INTRODUCTION1.1—Background

Significant revisions were made in Chapter 9 of ACI 318-02to the load factors to be used for determining requiredstrength. The load factor for dead load was reduced from 1.4to 1.2, and the load factor for live load was reduced from 1.7to 1.6; other changes were also made as given in equationsfor required strength in Chapter 9. The strength-reductionfactors (φ-factors) were also modified. The φ-factor for shearand torsion was reduced from 0.85 to 0.75, while the φ-factorfor compression-controlled members was reduced from 0.70to 0.65 unless spiral reinforcement is provided. The φ-factorfor tension-controlled members (most flexural members)was not reduced, and remains 0.9.

The load factors and load combinations of ACI 318-05match those of ASCE 7-02 (American Society of Civil Engi-neers 2002). The changes were made to unify the load factorsused to design concrete structures with those generally usedto design structures constructed of other materials, such asstructural steel. The changes also facilitated the design of

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concrete structures that included members of materials otherthan concrete.

Chapter 20 (Strength Evaluation of Existing Structures) of318-02 and 318-05 was not changed from the previous codewith regard to load test procedures. Section 20.3.2 (LoadIntensity) of ACI 318-02 was not changed from the 1999edition; that is, the total test load (including dead loadalready in place) was still defined to be not less than0.85(1.4D + 1.7L), with live load permitted to be reduced inaccordance with the applicable building code.

The reduction in load factors used for computing requiredstrength without a corresponding reduction in the test loadintensity resulted in two effects. First, the test load was nolonger a fixed percentage of the required strength. Second,the test load was now in the range of 93 to 98% of therequired strength for tension-controlled sections rather than85% of the required strength as was the case in ACI 318-71through 318-99.

ACI Committee 318 requested that Committee 437 reviewand report on the load intensity requirements of Chapter 20.In the process, Committee 437 has undertaken a thoroughreview of the historical background of load testing anddeveloped not only recommendations for revisions to the testload magnitude (TLM), but also to the protocol for loadtesting and the acceptance criteria used to evaluate the results.

1.2—IntroductionThe provisions of Chapter 20 of ACI 318 have remained

essentially unchanged for an unprecedented period of timesince the publication of ACI 318-71, when the code waschanged from working stress design to ultimate strengthdesign. Before the 1971 code, the test load requirements oracceptance criteria were revised with almost every newedition of the code dating back to 1920. Chapter 3 and
Appendix B of this report provide a detailed review of the history of the load test requirements and acceptance criteriain ACI 318. They also provide a discussion of other interna-tional standards and of significant research and reporting ofother organizations on the subject of load testing.
The changes made in the load factors and load combina-tions of ACI 318-05 require a re-examination of the load testrequirements of Chapter 20 of ACI 318-05. This reportpresents the recommendations of Committee 437 for revisionsto the requirements of Chapter 20. Three key areas areaddressed: load factors to be used in defining the TLM; theload test protocol; and acceptance criteria.

As will be discussed further in Chapter 4, the purposes of
the recommended revisions to the TLM definition are twofold.The first purpose is to define a test load that will demonstratea consistent safe margin of capacity over code-requiredservice live load levels. Secondly, the definition of the testload primarily in terms of service live load rather than required(ultimate) strength is meant to emphasize the fact that loadtesting is (typically) a proof loading. In the experience of thecommittee members, most structures being load tested passwith small deflections. Load testing does not typically providean indication of the ultimate strength of the structure, and thatindication usually is not the goal of load testing.--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---
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LOAD TESTS OF CONCRETE STRUCTURES 437.1R-3

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Since 1920, the acceptance criteria used with load testinghave incorporated a limit on measured maximum deflectionsafter a 24-hour holding period of the total test load. Thecurrent criteria have not changed since ACI 318-63.Currently, the deflection limit is described by the formulaΔmax ≤ lt

2/20,000h. The theoretical basis for this formula hadits origins in the first decades of the 20th century. Thecommittee has researched the origins of the formula and re-evaluated its appropriateness. The committee recommendsadopting other more meaningful deflection acceptance criteria.

Chapters 5 and 6 of the report discuss selection of a load
test protocol and recommended changes to the acceptancecriteria used in strength evaluation and load testing.Committee 437 in its report 437R-03, “Strength Evaluationof Existing Concrete Buildings,” has discussed a cyclic loadtest method that offers advantages in terms of reliability andunderstanding of structural response to load when comparedwith the conventional static load test. Chapter 6 presentsrecommended acceptance criteria for both the 24-hour statictest and for the cyclic test. Acceptance criteria for service-ability are also given.
1.3—LimitationsProcedures and recommendations provided in this report

are intended for structures and buildings using concretes ofnormal strengths. The methods are not intended for bridges,structures with unusual design concepts, or other specialstructures. The methods are not intended to be used forproduct development testing where load testing is used forquality control or approval of mass-produced members. Testingfor resistance to wind and seismic loads is not discussed.AASHTO provisions for load testing of bridge structures areoutside the scope of this report. Load testing to determineultimate strength is also outside the scope of this report.

CHAPTER 2—NOTATION AND TERMINOLOGY2.1—Notation

The notations reported in this section refer to the symbolsused in the numbered chapters.h = overall thickness of member, in. (mm)lt = span of member under load test; units depend on

structural member considered (ACI 318)s = average spacing between cracks, in. (mm)D = total dead load: Dw + Ds; units depend on

structural member consideredDs = superimposed dead load; units depend on structural

member consideredDw = dead load due to self-weight; units depend on

structural member consideredF = loads due to weight and pressure of fluids with

well-defined densities and controllablemaximum heights; units depend on structuralmember considered

IDL = deviation from linearity index, dimensionlessIP = permanency index, dimensionlessIR = repeatability index, dimensionlessL = live loads produced by use and occupancy of the

building not including construction, environ-can Concrete Institute

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mental loads, and superimposed dead loads; unitsdepend on structural member considered

Lr = roof live loads produced during maintenance byworkers, equipment, and materials or during lifeof structure by moveable objects such as plantersand people; units depend on structural memberconsidered

P = applied load during load test (Fig. 6.1 and 6.2)

r

Pi = load of point i in load-deflection envelope forcomputation of IDL acceptance criterion (Fig. 6.2)

Pmin = minimum load to be maintained during load test(typically 10% of total test load)

Pref = reference load for computation of IDL acceptancecriterion (Fig. 6.2)

R = rain load, or related internal moments and forces;units depend on structural member considered

S = snow load; units depend on structural memberconsidered

TL = test load per ACI 318 before 1971; units dependon structural member considered

TL05 = TL99 = test load per ACI 318-71 through ACI318-05 = 0.85(1.4D + 1.7L) = 1.19D + 1.44L;units depend on structural member considered

TLM = test load magnitude (including dead load alreadyin place); units depend on structural memberconsidered

U = required strength to resist factored loadsU99 = required strength per ACI 318-99 = 1.4D + 1.7LU05 = required strength per ACI 318-05 = 1.2D + 1.6Lαi = slope of secant line of point i in load-deflection

envelope, degreesαref = slope of reference secant line in load-deflection

envelope, degreesΔεs = strain difference in longitudinal reinforcementΔi = deflection of point i in load-deflection envelope for

computation of IDL acceptance criterion (Fig. 6.2)Δmax = measured maximum deflection, in. (mm)Δref = reference deflection for computation of IDL

acceptance criterion (Fig. 6.2)Δr max= measured residual maximum deflection, in. (mm)ΔA

max= maximum deflection in Cycle A under maximumtest load, in. (mm)

ΔAr = residual deflection after Cycle A under minimum

test load, in. (mm)ΔB

max = maximum deflection in Cycle B under maximumload, in. (mm)

ΔBr = residual deflection after Cycle B under minimum

test load, in. (mm)φ = strength-reduction factor as per ACI 318

2.2—TerminologyThe following definitions are important to the under-

standing of this report.acceptance criteria—a set of explicit and quantitative

rules to determine whether or not a structure (or a portion ofit) passes a load test.

dead load (D), total—in this report, a distinction is madebetween dead load due to self-weight and superimposed

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CHAPTER 3—HISTORY OF LOAD TEST, LOAD FACTORS, AND ACCEPTANCE CRITERIA

dead loads. Total dead load D will include both dead loaddue to self-weight and superimposed dead loads; that is, D =Dw + Ds. This definition creates a distinction not used in ACI318 or the International Building Code (IBC).

dead load (Dw), self-weight—dead load due to self-weight Dw is to include the weight of the concrete structuralsystem only.

dead load (Ds), superimposed—this report uses superim-posed dead load to designate all other weight of materials ofconstruction incorporated into a building other than self-weight of the concrete structural system. Such loads include,but are not limited to, partitions, floor finishes, nonstructuraltopping slabs and overlays, roofing materials, ceilingfinishes, cladding, stairways, fixed service equipment, andlandscaping, including fixed planters, soils, and plantings.

failure—when referred to the performance of a structure(or a portion of it) under load test, it indicates that one ormore acceptance criteria are not met.

proof load and proof load ratio—proof load is used todescribe a load applied to a structure with intent to prove asafe margin of satisfactory performance beyond code-required service live and dead loads. For this reason, proofload is defined in terms of service loads and not in terms ofrequired or ultimate strength. A proof load is generally notintended to provide an indication of the ultimate strength ofthe structure. Arithmetically, the proof load ratio is definedas the TLM minus the total dead load divided by the servicelive load; that is, proof load ratio = (TLM – D)/L.

strip or patch test load—a test load distributed over alimited portion of the tributary area of the structure ormember to be tested and typically applied by means ofhydraulic jacks.

test load magnitude (TLM)—TLM is defined as allexisting dead load due to self-weight and existing superim-posed dead load plus additional test loads used to simulateeffects of factored service live loads and factored superim-posed dead loads. The factors to be applied to live loads andsuperimposed dead loads to establish the TLM are providedin Chapter 4. The factor for superimposed dead loads is to beapplied to both existing superimposed dead loads and thosenot already in place.

3.1—Scope of historical reviewAn extensive review of the existing literature has been

done to develop a history of load testing of reinforcedconcrete structures. The results of this work are reported indetail in Appendix B. The focus of this literature search hasbeen in the following areas that are under consideration forrevision in ACI 318:• The purpose or goal of load testing, and the types of

load tests that should be used;• Development of appropriate superimposed loads to be

used in a load test; and• Establishment of appropriate acceptance criteria for

structural response to those test loads.t American Concrete Institute

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Appendix B begins with a history of the development ofload testing within the United States and development ofACI building code requirements for load testing. Thissection of the appendix is followed by a section presentinggeneral discussion of work done by various organizations inthe United States and around the world in the area of loadtesting of concrete structures. The purpose of Appendix B isto provide a historical perspective of changes to ACI 318recommended by Committee 437. It serves to show theorigins of the present state of practice and why changes areconsidered appropriate. It provides a discussion of researchon and practices for load testing outside the United States.

3.2—Summary and conclusionsThe key points drawn from the literature survey and

derived conclusions are provided herein.3.2.1 Purpose of load testing1. Load testing originated in the late 1800s as proof (or

acceptance) testing to show that a structure could resistspecified service loads with a reasonable margin of safetyagainst failure. It was generally not employed to determinethe ultimate strength of a concrete member;

2. Provisions for load testing in ACI 318 and prevailingindustry interpretations of those provisions have, over time,blurred to imply that the purpose of load testing is: 1) toensure that the structure being tested meets the requirementsof ACI 318; and 2) to assess the ultimate strength of thatconcrete structure; and

3. Consideration of historical information and datasuggests that the purpose of load testing should be dividedinto three distinct categories:

a. Proof testing to show that a structure can safely resistintended design loads with an adequate factor ofsafety against failure;

b. Proof testing to show that a structure can resist theworking design loads in a serviceable fashion wheredeflections and cracking are within limits consideredacceptable by ACI 318; and

c. Testing to failure to show the ultimate capacity of astructural member either in the field or as a model ina laboratory setting.

3.2.2 Test load magnitude1. The test load magnitude used in U.S. load testing practice

generally originated as two times the live load. This criterionhas been found in the oldest references reviewed, includingthose dating into the late 1890s. The exact origin of this testload has not been found. It is believed to be a rule of thumbthat was adopted in that era;

2. This test load was used for structures designed usingallowable stress design techniques that are generally nolonger used in the United States;

3. The criterion for using a superimposed test load of twotimes the live load was abandoned by ACI in 1963, althoughit continued to persist in various local and state buildingcodes well beyond that time;

4. Load test practice in ACI did not change to any appreciabledegree when ultimate strength design was introduced to theACI 318 code in 1963 and 1971. Ultimate strength design


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CHAPTER 4—LOAD FACTORS

methods generally resulted in a lower factor of safety againstfailure than allowable stress design methods, and theresulting designs were often more flexible than those of theearlier methods. The TLM was scaled back approximately10%; however, the deflection criteria remained unchanged;

5. Over time, the TLM has been modified in ACI 318 froma high of TL = 1.5D + 2.0L to the current low of TL =0.85(1.4D + 1.7L), which equates to TL = 1.19D + 1.44L. Asshown in Table B.4, no agreement exists regarding load
factors for defining the test load magnitude in similardocuments throughout the world. Ideally, a minimum factorof safety should be explicitly agreed upon in terms of TLM;
6. It is suggested that a load level consisting of the serviceload equal to 1.0D + 1.0L should be included in the load testprocedure to provide for assessment of the serviceability ofthe structure. Deflections and crack widths should becompared with maximum allowable, code-defined, ordesirable values; and

7. More specific criteria should be developed to definewhat constitutes visible evidence of failure.

3.2.3 Protocol for application of the load test1. Modern practice for load testing seems to be turning in

the direction of applying the test load in increments thatinclude multiple cycles of incremental loading andunloading until the full desired test load is attained. Thisappears to have benefits relative to ensuring that the structureis adequately and properly responding to the desired test loadin terms of deflection and deflection recovery;

2. Load test practice should include application of one ormore preliminary load tests at values well below the fulldesired superimposed test load to assess the conditions ofend restraint and fixity acting in the portion of the structurebeing tested and to identify the degree of load sharing that isoccurring from the member being loaded to the surroundingmonolithic or structurally attached members; and

3. Duration of the application of the full desired test loadhas historically been set at 24 hours. Because a sufficientcorrelation of shorter-term tests with 24-hour tests has notbeen found, the 24-hour holding period at full TLM shouldbe retained in the code to take creep of concrete into consid-eration (even if to a limited extent) and to allow the structureto properly respond and adjust to the maximum test load.

3.2.4 Acceptance criteria for load testing3.2.4.1 Use of maximum deflection

1. The current acceptance criterion for maximum allowabledeflection (that is, Δmax = lt

2/20,000h) in a load test wasdeveloped for simple span members and does not adequatelyreflect any variations in end fixity of structural membersfrom that condition. Further, that equation was developedduring the era of allowable stress design methods. The equationis based on concepts of uncracked sections and maximumallowable stress in concrete. The allowable stress and elasticmodulus built into the equation were derived for lower-strength concrete than is often employed in design today.The equation does not take into account the actual strength andstiffness of the concrete in the member being tested;

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2. No correlation exists between structural response to atest load of TL = 0.85(1.4D + 1.7L) and the deflection criteriathat are currently being used in ACI load test practice;

3. The maximum deflection of a structure following appli-cation of a test load should be compared, where possible,against calculated values using the best available calculationmethods that are based on thorough and comprehensive fieldinvestigation of the physical and mechanical properties of theconcrete in the area of the structure under investigation; and

4. It is the current provision of IBC 2003 to limit deflectionsduring load tests to values established as simple percentagesof the span (for example, lt /360) relating to serviceabilitycriteria.

3.2.4.2 Use of deflection recovery1. With the single exception of work done and reported in

Israel in 1950 (Arnan et al. 1950), historical load test practicesuggests that deflection recovery can be properly used as anacceptance criterion for load testing of concrete structures.The concerns expressed in the 1950 Israeli report regardingdeflection recovery can be addressed through implementationof a load test practice that includes preliminary load testingor application of the test load in several cycles of loading andunloading of the structure in increasing increments until thefull test load is in place;

2. Historical practice suggests that the deflection recoveryafter 24 hours in a static load test, without incremental loadingand unloading of the structure as suggested previously,should be at least 75%. The Israeli research and more currentwork with cyclic load testing suggest that the deflectionrecovery requirement should be significantly higher, on theorder of 90%, when using the cyclic load test method or whenretesting a structure using the static load test method; and

3. Alternative methods of analyzing deflection recoverydata to establish new criteria for acceptance have been intro-duced recently to accompany the cyclic load test method. Ifcyclic load testing is to be incorporated into ACI 318, thenthe appropriate accompanying deflection recovery acceptancecriteria need to be defined.

4.1—IntroductionA revised definition of TLM should be developed to

address the change of load factors and load combinationsused in ACI 318-05 for defining required strength comparedwith load factors used in ACI 318-71 through 318-99. Thenew definition should address concerns regarding whetherstructures designed by earlier codes should have differentTLMs than structures designed in accordance with ACI 318-05.The new definition should also address whether the load testwill be performed on all suspect portions of a structure oronly on selected limited areas.

This chapter presents recommendations for revisions tothe definition of test load magnitude (TLM). The TLM isintended for proof testing; that is, load testing to show that astructure can safely support code-required service loads.Load testing to determine ultimate strength is outside thescope of this report.

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Table 4.1—Design strength and test load comparison: full load test*

Type offacility

Dw,

lb/ft2†

(kN/m2)(1)

Ds ,

lb/ft2 (kN/m2)

(2)

L ,lb/ft2

(kN/m2)(3) (4)

U99,

lb/ft2 (kN/m2)

(5)

U05,

lb/ft2 (kN/m2)

(6) (7)

TL05,

lb/ft2 (kN/m2)

(8) (9) (10) (11)

TLM ,lb/ft2

(kN/m2)(12) (13) (14) (15) (16)

Parking slab, unreducedlive load

65(3.11) — 50

(2.39) 0.77 176 (8.43)

158(7.57) 0.90 150

(7.18) 0.95 1.30 1.69 135(6.46) 0.90 0.85 0.77 1.40

Parking beam,reducedlive load

100(4.79) — 30

(1.44) 0.30 191 (9.15)

168 (8.04) 0.88 162

(7.76) 0.97 1.25 2.08 142 (6.80) 0.87 0.85 0.74 1.40

Office slab,unreducedlive load

65(3.11)

20 (0.96)

50 (2.39) 0.59 204

(9.77)182

(8.71) 0.89 173 (8.28) 0.95 1.28 1.77 157

(7.52) 0.91 0.86 0.77 1.44

Storage, light 110 (5.27) — 125

(5.99) 1.14 367(17.57)

332(15.90) 0.91 312

(14.94) 0.94 1.33 1.61 285(13.65) 0.91 0.86 0.78 1.40

Storage, light with heavierstructure

150(7.18) — 125

(5.99) 0.83 423(20.25)

380(18.19) 0.90 359

(17.19) 0.95 1.31 1.67 325(15.56) 0.90 0.86 0.77 1.40

Storage, heavy 150(7.18) — 250

(11.97) 1.67 635(30.40)

580(27.77) 0.91 540

(25.86) 0.93 1.35 1.56 500(23.94) 0.93 0.86 0.79 1.40

Manufacturing,very heavy

175(8.38) — 400

(19.15) 2.29 925(44.29)

850(40.70) 0.92 786

(37.63) 0.93 1.37 1.53 735(35.19) 0.93 0.86 0.79 1.40

Landscaped pedestrian plaza

200(9.58)

300‡

(14.36)100

(4.79) 0.20 870(41.66)

760(36.39) 0.87 740

(35.43) 0.97 1.23 2.40 670(32.08) 0.91 0.88 0.77 1.70

Plaza,truck dock

200(9.58) — 250

(11.97) 1.25 705(33.76)

640(30.64) 0.91 599

(28.68) 0.94 1.33 1.60 550(26.33) 0.92 0.86 0.78 1.40

Average — — — — — — 0.90 — 0.95 1.31 — — 0.91 0.86 0.77 1.44*TLM definition for testing all suspect portions of structure.†1 lb/ft2 = 47.88 N/m2.‡Landscaped pedestrian plaza value of 300 lb/ft2 (14.36 kN/m2) is not defined by ASCE-7, but is selected herein for illustrative purposes to represent 2.5 ft (0.76 m) of uniformlydistributed saturated soil weighing 120 lb/ft3 (1922 kg/m3) such as might be encountered in a large fixed planter containing trees.

Definitions:Dw = dead load to self-weight; Ds = superimposed dead load; D = Dw + Ds = total dead load; and L = live load.U99 = required strength per 318-99 = 1.4D + 1.7L.U05 = required strength per 318-05 = 1.2D + 1.6L.TL05 = TL99 = test load per 318-71 through 318-05 = 0.85(1.4D + 1.7L) = 1.19D + 1.44L.TL99/U99 = 0.85 for any value of D and L.TLM = proposed test load magnitude = 1.0Dw + 1.1Ds + 1.4L (simplified by assuming F, Lr , S, and R equal to 0).

LD----

U05

U99

--------TL05

U05

----------- TL05

D L+--------------

TL05 D–L

---------------------TLMTL05

------------ TLMU05

------------ TLMU99

------------ TLM D–L

----------------------

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4.2—Load factors for various components of service load

4.2.1 Reasons for change—The required strength U (anddesign strength) of tension-controlled members of structuresdesigned in accordance with ACI 318-02 and 318-05 hasbeen reduced compared with the required strength perprevious editions of ACI 318. As a result, the test load asdefined in Chapter 20 of ACI 318-02 and 318-05 is not afixed percentage of the required strength.

Table 4.1 provides a comparison of required strengths asdefined in ACI 318-99 and 318-05 for a variety of structures.The table assumes that the members being considered (slabsand beams) are not over-reinforced and therefore qualify astension-controlled members, which is usually the case inmost concrete structures. Representative values for dead andlive loads as shown in Columns 1, 2, and 3 are taken fromtypical buildings. Column 4 shows that the live load to totaldead load ratio varies from 0.20 to 2.29. Columns 5 and 6show the total factored demands (or minimum requiredstrengths) according to ACI 318-99 and 318-05, whileColumn 7 shows their ratios. Column 8 shows the test loadcomputed according to ACI 318-05. Note that while the ratioof test load to required strength in ACI 318-99 was 0.85, the

right American Concrete Institute ded by IHS under license with ACI
ratio of test load (TL05) to required strength (U05) defined byACI 318-05 varies from 0.93 to 0.97 for the selected examplesas shown in Column 9.

In Table 4.1, Columns 9 and 10 provide a comparison ofthe test loads as defined in ACI 318-05 with requiredstrength and total service loads. Note that the ratio of testload to total service loads varies from 1.23 to 1.37 for theexamples provided, which is a reasonably close range. Thetable also provides in Column 11 a comparison of the testload minus the total dead load divided by the live load (theproof load ratio). Note that this ratio varies from 1.53 to 2.40,which is a considerably wider spread.

A consequence of defining the test load as a constantpercentage of the required design strength is that the rela-tionship between the proof load applied to the structure andthe service live load is not apparent and is not a reasonablyconstant ratio. The variation in this ratio is among thereasons the TLM should be redefined, the goal being moreconsistent proof testing of structures.

It is recommended that the TLM be redefined in terms ofproof loading rather than as a percentage of requiredstrength. As discussed in Chapter 3, proof loading has histor-ically been the purpose of load testing. The proof load ratio--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

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readily reveals the factor of safety of test load over serviceloads, and therefore adds clarity to the intent of load testing.

As noted in Chapter 3, ACI 318 has wavered on whethersome additional percentage of the design dead load shouldbe included in the test load. Defining the test load as a combi-nation of factored design dead and live loads is not unique toACI. Introducing a factor other than 1.0 for dead loads indefining the TLM makes the relationship between the TLMand the service live loads variable (that is, a function of therelative magnitude of the dead loads and live loads). Asshown in Table 4.1, when the ratio of live load to dead plussuperimposed dead loads is small (Column 4), the test loadas defined in ACI 318-05 approaches the required strength(Column 9). This relationship tends to penalize structuresthat are heavy compared with the live loads they supporteven though calculation of a substantially accurate dead loadis achievable on existing structures. This aspect of thecurrent test load definition is another reason modifications tothe definition of the TLM are recommended.

4.2.2 Recommended changes to test load magnitude—Asdefined in Section 2.2, a proof load is a load applied to astructure to prove a safe margin of satisfactory performancebeyond code-required service live and dead loads. It isproposed that the proof load be defined in terms of thoseparts of the total load a structure will likely be subjected tothat are variable. Therefore, when defining proof load,unlike when defining required strength, there is a need toseparate the components of dead load that do not vary fromthose that do. For this reason, dead load is separated into twocategories: dead load due to self-weight (Dw) and dead loaddue to weight of construction and other building materials(Ds). This latter category is defined as superimposed deadloads and, as noted in Section 1.3, includes weights offinishes, cladding, partitions, and fixed landscaping elements.

Dead load due to self-weight should be based on the as-constructed dimensions of those portions of the structure tobe tested or dimensions of the structural members that areconsidered to be representative of the as-built structure, ifdifferent. Because this is a known and existing load, there isno need to apply a factor greater than unity to this self-weightwhen defining the test load as a proof load.

Superimposed dead loads may be defined by the localbuilding code or may be defined in the design documents forthe structure. Because these loads represent a variable thatmay change over time depending on the owner's use of thefacility and construction and maintenance means andmethods, a factor greater than 1.0 is suggested for superim-posed dead loads. The actual factor used will depend on thedegree of variability anticipated by the engineer defining theload test or by the building official. A load factor of 1.1 isrecommended for superimposed dead loads except asdiscussed herein.

For partial load testing (when only portions of the suspectareas of a structure are to be tested), a higher test load isrecommended to improve the level of confidence that signif-icant flaws or weaknesses in the design, construction, orcurrent condition of the structure are made evident by theload test. This recommendation reinstitutes the format of

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ACI 437R-67, in which two different test load definitions wereprovided. The exception in these current recommendations iswhen the members to be tested are determinate (for example,cantilevers or simple span members) and the possibilityexists of producing an inelastic response in the members ifthe test load approaches the design strength too closely.While the new strength-reduction factors of ACI 318-05provide for a higher nominal strength with respect to designor required strength than did the factors of ACI 318-99, thenew factors are still based not only on desired reliability, butalso on probable inaccuracies in design or construction; foran existing structure, these latter concerns mean that it is notpossible to know how great the buffer between designstrength and nominal strength is. Therefore, for determinatemembers, the lower TLM is recommended.

Where the suspected shortcoming or weakness amongstructural members is highly variable throughout the structure(for example, corrosion and debonding of embedded reinforcingsteel), it is critical that the engineer select areas for testingthat represent conditions believed to be severe with respectto the safety and performance of the structure. It is importantto note that it is not only the severity of damage to the structuralmember, but rather the combination of severity with thelocation of minimum strength reserve that is of most interest.The percentage increase in TLM recommended as followsfor partial tests will not significantly improve probabilitythat the tested structure can safely support code loads if thetested areas are not well chosen.

It is recommended that the load intensity as provided inSection 20.3.2 of ACI 318-05 be defined as follows. Theequations are proposed to be consistent with the load combi-nations of Chapter 9.

Load intensity—When all suspect portions of a structure areto be load tested or when the members to be tested are deter-minate and the suspect flaw or weakness is controlled byflexural tension, the test load magnitude, TLM, (includingdead load already in place) shall not be less than

TLM = 1.2(Dw + Ds) (20-1)

or

TLM = 1.0Dw + 1.1Ds + 1.4L + 0.4(Lr or S or R) (20-2)

or

TLM = 1.0Dw + 1.1Ds + 1.4(Lr or S or R) + 0.9L (20-3)

whereDs = superimposed dead load;Dw = dead load due to self-weight;L = live loads, or related internal moments and

forces;Lr = roof live load, or related internal moments and

forces;R = rain load, or related internal moments and

forces; andS = snow load, or related internal moments and forces.--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---


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When only part of suspect portions of a structure is to be loadtested and members to be tested are indeterminate, the TLM(including dead load already in place) shall not be less than

TLM = 1.3(Dw + Ds) (20-4)

or

TLM = 1.0Dw + 1.1Ds + 1.6L + 0.5(Lr or S or R) (20-5)

or

TLM = 1.0Dw + 1.1Ds + 1.6(Lr or S or R) + 1.0L (20-6)

Ds = superimposed dead load;Dw = dead load due to self-weight;L = live loads, or related internal moments and

forces;Lr = roof live load, or related internal moments and

forces;R = rain load, or related internal moments and

forces; andS = snow load, or related internal moments and forces.

In Eq. (20-2), the coefficient of the live load shall be permittedto be reduced in accordance with the requirements of theapplicable Model Code or General Building Code. If impactfactors have been used for the live load in design of thestructure, then the same impact factor should be included inthe above equations.

The total dead load shall include all superimposed deadloads, Ds, considered in design or considered by the engineeror building official to be relevant to the proposed load test.Where superimposed dead loads represent a significantportion of the total service loads, are not already in place on

Table 4.2—Design strength and test load comparison: partial load test*

Type of facility

TLM , lb/ft2

(kN/m2)(12) (13) (14) (15) (16)

Parking slab,unreduced live load 145 (6.94) 0.97 0.92 0.82 1.60

Parking beam,reduced live load 148 (7.09) 0.91 0.88 0.77 1.60

Office slab,unreduced live load 167 (7.99) 0.96 0.92 0.82 1.64

Storage, light 310 (14.84) 1.00 0.93 0.85 1.60

Storage, light with heavier structure 350 (16.76) 0.97 0.92 0.83 1.60

Storage, heavy 550 (26.33) 1.02 0.95 0.87 1.60

Manufacturing,very heavy 815 (39.02) 1.04 0.96 0.88 1.60

Landscape pedestrian plaza 690 (33.04) 0.93 0.91 0.79 1.90

Plaza, truck dock 600 (28.73) 1.00 0.94 0.85 1.60

Average — 0.98 0.92 0.83 1.64*TLM definition for testing only part of suspect portions of structure.

Definitions:TLM = proposed test load magnitude = 1.0Dw + 1.1Ds + 1.6L (simplified by assuming F,Lr, S, and R equal to 0).

TLMTL05

------------ TLMU05

------------ TLMU99

------------ TLM D–L

----------------------

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the structure, and/or may not be of controllable intensity, afactor greater than 1.1 shall be considered for the superim-posed dead load in the above equations for calculating thetest load magnitude.

The commentary to this section in the building code couldprovide further explanatory discussion on this paragraph; forexample, the possible variability of soil loading intensity andconstruction equipment loads on a landscaped structure. Forthis example, if soil loads are not already in place on thestructure to be tested, then it will likely be appropriate toincrease the test load magnitude by using a factor such as 1.4or 1.6 to account for the variability of the loads the structurewill be subjected to during installation of the soils and otherlandscaping features.

Commentary language should be provided in the buildingcode to caution users when testing structures designedaccording to Chapter 9 of ACI 318-02 or 318-05 that, forsome structures, the test load may induce bilinear elastic(cracked) or inelastic behavior. Discussion is provided inChapter 5 regarding linearity of response as part of acceptancecriteria recommended for adoption in ACI 318.

When testing members not meeting the minimum shearreinforcement requirements of ACI 318-05, Section 11.5.6.1but meeting strength requirements on the basis of Section11.5.6.2, an assessment of the test load at which significantcracking or damage in the web-shear region will occur isrecommended. Significant cracking that does not close afterremoval of the test load may result if nonprestressed rein-forcement yields during the load test or if the web shearregion has no nonprestressed reinforcement. An appropriateadjustment of the proof load may be required to preventpermanent damage (that is, permanent open cracking) to suchmembers. Equations (20-1) through (20-3) are recommendedfor determining TLM for such cases.

Tables 4.1 and 4.2, Column 12, provide the value of theproposed TLM for the example structures selected for fulland partial load tests, respectively. Comparisons of the TLMwith the total test load and required strength defined by ACI318-05 are given in Columns 13 and 14, respectively. Asshown in Table 4.1, the proposed TLM definition for fullload tests has the effect of reducing the test load by approxi-mately 10% compared with the test load of ACI 318-05(Column 8), and so also reduces the TLM relative to requiredstrength. In fact, the TLM is typically about 86% of therequired strength per ACI 318-05 (Column 14) and about77% of required strength per ACI 318-99 (Column 15). Noexamples have been provided of structures supporting fluidloads; however, the 1.2 factor recommended is 86% of theload factor for fluid loads F provided in Chapter 9 of ACI318-05 for defining required strength U, and thus wouldproduce a TLM versus required strength ratio consistent withthe ratio for structures with live loads L, Lr, R, and S.

The proposed TLM definition for partial load tests whereonly parts of the suspect areas are to be tested results in a testload close in magnitude to the test load of ACI 318-05,varying from 91 to 104% of the current test load for theexample structures as shown in Column 13 of Table 4.2.


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Proposing a ratio of the TLM to the required strength ofapproximately 85% for full load testing is, of course, notaccidental. The ratio of test load to required strength wasexplicitly set at 85% in 1971. Calculations made by membersof Committee 437 also indicate that the ratio of the TLM toultimate strength appears generally to have been on the orderof 80 to 85% in previous allowable stress design versions ofthe code. That is to say, one can design a slab or beam usingthe allowable stress design methods and typical materialsstrengths of the 1940s and 1950s, and then calculate theresulting nominal strength using current principles. If onethen calculates the TLM defined in earlier editions of ACI 318(for example, ACI 318-51 and 318-56) and compares thatwith the nominal strength of the designs that resulted fromthose code provisions, it turns out that the ratio is oftenapproximately 80 to 85%. Thus, having an upper limit to theTLM of about 85% of required strength has considerablesustained history in ACI. This limit is furthermore consid-ered prudent to avoid possibly causing excessive inelasticdeformations in a structure as a result of load testing.

A concern, but unavoidable consequence, of maintainingthe ratio of TLM to required strength at 85% is that with thereduced load factors of ACI 318-05, the proven factor ofsafety resulting from load testing would now be lower thanat any time in the history of ACI. The proof load ratio thatresulted from the TLM defined in ACI 318-71 through 318-05has typically been on the order of 1.7 (Column 11). Theproof load ratio resulting from the new TLM would typicallybe 1.4 when all suspect portions of a structure are to betested, or 1.6 when only part of the suspect portions are to betested. With respect to international standards, however, thisremains about average. In addition, as a practical matter,because most load tests involve testing only part of the suspectportions of a structure, the proposed Eq. (20-4) through (20-6)will generally control and provide a TLM that is roughly 90 to95% of the required strength and, for most of the examplespresented, is close to the TLM of ACI 318-05.

The recommended new TLM provides a rational balancebetween providing an adequate factor of safety, but not causingdamage to the structure in the process. Refer also to Section 4.3

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,,,

4.3—Load factors for extreme ratios of live loadto total dead load

Service conditions where the ratios of live load to totaldead load are considered outside the normal range aredefined as follows

(4-1)

For structures where L/(Dw + Ds) < 0.50, the load factorsapplied to the dead load due to self-weight and superimposeddead load in the recommended new TLM definition achievetwo ends. First, they remove the potential penalty againststructures with large self-weight compared with the liveloads they carry by eliminating the extra dead load compo-nent of the test load. They also reduce the TLM as apercentage of the required strength per ACI 318-05compared with the test load defined in ACI 318-05 versusrequired strength. As can be seen in Table 4.1, Column 14,the ratio of the proposed new TLM to required strengthremains nearly constant, regardless of the L/D, whereasColumn 9 shows the penalty assigned to structures with lowL/D by the current test load definition. For partial loadtesting, the ratio is not as constant, and Column 14 of Table 4.2shows that structures with higher L/D ratios also have largerTLMs relative to their required strength, but the TLMs arenot significantly different than the current test load.

It is recommended that the load factor for the live loadcomponent of the service loads for such structures with L/Dless than 0.50 be the same as for structures falling in thenormal range of L/D. The minimum TLM given by Eq. (20-1)and (20-4), however, provides an additional lower bound tothe test load that will apply in those cases where the live-deadload ratio is very small (L/D less than 0.15), where the factoredlive load does not provide a sufficiently large proof load withrespect to the self-weight and superimposed dead loads.

LDw Ds+------------------- < 0.50, where 0.50 is lower limit of normal range

LDw Ds+------------------- > 2.0, where 2.0 is upper limit of normal range ⎩

⎪⎨⎪⎧

-`-`,,`,,`,`,,`---

of this report regarding modifications to load factors.4.2.3 Applicability of TLM to structures designed per

earlier codes—The new TLM should be considered applicablefor existing structures regardless of the code under whichthey were designed. The nominal strength of tension-controlled members designed in accordance with the provisionsof ACI 318-71 through 318-99 was approximately 10%greater than those designed per 318-05, but generally at least10% less than members designed according to the allowablestress method of earlier codes. Members designed accordingto the earlier allowable stress methods would have beensubjected to higher TLMs using the test loads of ACI 318-51and 318-56. As discussed previously, the ratio of these TLMsto the members’ nominal strength would have been on theorder of 80 to 85%. Therefore, applying test loads defined by318-71 through 318-05 to structures designed according toearlier codes tests them to a lower percentage of their nominalstrength. This method has become accepted practice.--`,`,,```,,`,```,`,`,```,``,

Model building codes such as IBC provide that thestrength of structures designed per earlier codes is to becalculated according to the current code. Committee 437, inits reports ACI 437R-67 through 437R-03, has stated thatstrength evaluation of existing structures by analyticalmeans is to be based on principles of strength design asapplied in ACI 318 (using current principles).

Similarly, the proposed modified definition of the TLMshould be considered appropriate for strength evaluation ofstructures designed per earlier editions of ACI 318. If theproof load recommended herein provides an acceptablemargin of safety over maximum anticipated service loads fora structure designed in accordance with 318-05, then thesame factor of safety should be considered adequate forstructures designed in accordance with earlier codes. Theproposed TLM will be less than the test loads defined inearlier editions of ACI 318. Therefore, no inherent dangerexists of overloading such structures when using theproposed TLM.

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CHAPTER 5—LOAD TEST PROTOCOL

For structures with large live loads compared with thestructure’s self-weight and weight of other superimposeddead loads, that is, L/(Dw + Ds) > 2.0, the committee seesconflicting concerns. As noted in Chapter 3, the RILEMdocument TBS-2 recommends increasing the test load if thelive load exceeds twice the dead load, although that docu-ment does not provide further explanation of why anincreased factor of safety is considered appropriate norwhat the magnitude of that increased factor of safetyshould be. On the other hand, this approach could resultin situations where otherwise adequate structures areloaded into the inelastic range during the load test,inducing permanent deformations. This could occur, forexample, when testing a structure prestressed for a lower,more typical service load condition but reinforced withbonded reinforcement to provide adequate ultimatestrength for full code-required live load.

If the engineer and building official are of the opinion thatthe service live loads for a structure to be evaluated by loadtesting are known, controllable, and free from dynamicmagnification effects, it is recommended that the load factorto be used on the live load portion of the service loads bereduced to 1.2 and 1.3, respectively, for full and partial loadtests when L/(Dw + Ds) > 2.0.

The following text is proposed for inclusion in thecommentary for R20.3.2 of ACI 318:

For structures where the ratio of live load to total dead load(L/D) is larger than 2.0, the multiplier of the live load, L, canbe reduced from 1.4 to 1.2 in Eq. (20-2), and from 1.6 to 1.3in Eq. (20-5) when the engineer determines that the magni-tude of the live load is known and controllable and free fromdynamic magnification effects.

5.1—IntroductionTo apply test loads to a structure or portion of a structure

in a systematic fashion for purposes of evaluating safety andserviceability, a number of items should be considered. Theyinclude, but are not limited to: test load configuration, themeans by which the test load is applied, the procedure forapplication of the test load, and the duration of application ofthe test load. These items are discussed in this chapter. Inaddition, two common test methods are defined anddiscussed in general terms.

5.2—Test load configurationAccording to Chapter 20 of ACI 318-05, the test load must

be arranged to maximize the deflection and stresses in thecritical regions of the structural members under investigation.There are no other requirements for the configuration of thetest load. Several possible options could be used to satisfythe Chapter 20 requirements. The test load could be appliedso as to replicate the uniformly distributed load used fordesign, or the test load could be applied with a series ofconcentrated loads to simulate the effects of a uniformlydistributed load.

5.2.1 Uniformly distributed load pattern—Perhaps themost obvious way to determine if a structure is capable of

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carrying the loads for which it is designed is to apply thoseloads in the same load pattern that is assumed in the design.To simulate a uniformly distributed load condition, test loadsare commonly applied by means of dead weights, which isdiscussed in another section of this chapter. When test loadsare applied in a uniform pattern over the full structure or overa large enough area to fully load the critical member beinginvestigated as well as surrounding structural members thatcould contribute to supporting the load, then concerns suchas load sharing and end fixity need not be as thoroughlyinvestigated as when a small number of concentrated loadsare applied.

5.2.2 Patch or strip equivalent loads—Chapter 20 of ACI318-05 does not indicate the specific load distribution to beused; therefore, it is acceptable to apply equivalent concen-trated (or patch) loads by means of hydraulic jacks or othermethods. When using point loads applied by hydraulic jacks,it is difficult to determine the equivalent forces that willproduce the same effects, including bending moments andshear forces, as the uniformly distributed load used indesign. When planning a load test to determine the magni-tude of the concentrated equivalent loads, the engineer maymodel the structural behavior of the members through thefollowing methods:• Numerical approaches (for example, finite element

method) (Vatovec et al. 2002; Galati et al. 2004).Appropriate modeling is only possible given knowledgeof material properties, internal reinforcement location,and overall geometry;

• Simplified models that analyze a portion of staticallyindeterminate structures. In this instance, it is necessaryto have knowledge of the degree of fixity at the supportsand the load sharing offered by adjacent members;

• Trial tests. For those situations where no information isavailable on the construction, and budget constraintsdisallow invasive and nondestructive testing beforeconducting a load test, a load-unload cycle could beused for calibration of actual member fixities and loadtransfer characteristics. Current practice in Europe(Lombardo and Mirabella 2004) shows that an equivalentforce to substitute for uniformly distributed loads maybe calibrated based on the knowledge of the deflectionresponse of the member(s) and the surrounding structure.To this end, Appendix A presents a brief explanation of
the methodologies to be used to establish service loadand TLM in the case of a strip test load and patch testload(s).
5.3—Load application method5.3.1 Dead weights—To simulate a uniformly distributed

load condition, loads are commonly applied by means ofdead weight such as masonry block, sand bags, and water,either ponded or in barrels. Test loads can typically beapplied with rather unsophisticated technology, and do notrequire specialized equipment. Such procedures, however,lead to laborious and time-consuming activities for sitepreparation, affecting the overall cost of the load test. Inaddition, when test loads are applied by means of dead


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Fig. 5.1—Load tests and cycles for a cyclic load test.

uo

,

weights, there is generally no feasible way to rapidly removethe load. In case of failure, adequately designed shoringbecomes a critical safety measure.

5.3.2 Hydraulic jacks—The application of test loads usinghydraulic jacks, rather than uniformly distributed dead loads,allows for faster and more controlled application of testloads. When a structure that is loaded by displacement-controlled hydraulic jacks experiences a softening postpeakbehavior, the applied load decreases in a stable mannerbecause the displacement rate remains constant. An addedbenefit of applying test loads with hydraulic jacks is that thetest load can be removed almost instantaneously in case ofimpending failure. The use of hydraulics in the properconfiguration may also create less of a disturbance to theoccupants and finishes of the area being tested, thus resultingin a reduction of inconvenience to the users. While loadingby means of hydraulic jacks may provide benefits during aload test, there is a need to create a reaction system for thehydraulic jacks that requires design and could be expensiveand time consuming to implement. There are several ways toprovide reactions to the hydraulic jacks that depend on thecharacteristics of the member to be tested and the overall siteconditions. Several methods are defined in ACI 437R.

5.4—Loading proceduresTwo procedures are currently in use for the application of

test loads to buildings. The first has been used for many years,and involves applying loads in a monotonic fashion. The other,more recent, procedure applies test loads in a series of zeroto maximum load cycles that increase incrementally (Fig. 5.1).

5.4.1 Monotonic loading—In current practice, monotonicloading is the standard loading procedure because of practicalconsiderations and cost of placing and removing test loadsthat are commonly in the form of sand bags, water barrels,and other similar materials. Typically, loads are applied innot less than four approximately equal increments up to apredetermined maximum test load level. Data readings areusually taken at each loading stage. The time it takes to getto the maximum load depends on the test load configurationand the load application method as previously discussed.Monotonic loading is almost always used when the loads are--`,`,,```,,`,```,`,`,```,``

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being applied with dead weights because of the time it takesto apply and remove the loads. Monotonic loading can alsobe used when applying test loads with hydraulic jacks.

5.4.2 Cyclic loading—In the cyclic loading procedure, theloads are applied in loading-unloading cycles of increasingmagnitude using hydraulic jacks that are controlled by handor electric pumps. Using a sequence of loading andunloading cycles up to the predetermined maximum loadlevel provides the opportunity to work the structure andassess potential changes in response to repeated loading andto increasing load levels. The load sequence is intended toidentify, in an explicit manner, any undesirable response. Inrecent work (Mettemeyer 1999; Casadei et al. 2005), theresponse has been characterized by monitoring parameterssuch as: linearity of structural deflection response, repeat-ability of load-deflection response, and permanency ofdeflections. Because the structure is initially loaded andunloaded at low levels, the engineer has the ability to betterunderstand end fixity and load transfer characteristics of thetested member by comparing actual deflection responseswith calculated deflection responses. For statically indeter-minate structures in particular, this ability allows checkingthe accuracy of the assumptions made regarding fixity andload sharing used to plan the load test. The advantages ofcyclic loading are not yet fully understood because the database and experience obtained using this procedure arelimited, so additional validation is desirable.

5.5—Loading durationOnce the maximum test load has been reached, it is held in

place for a given amount of time. Depending on the testmethod that is used, this may be a short duration (approxi-mately 2 minutes) or up to as long as 24 hours.

5.5.1 Twenty-four hours at maximum load—For more than80 years, the maximum test load has been held for at least24 hours according to ACI 318 requirements. The strength ofconcrete under sustained load is known to be lower than thestrength under short-term load. The strength under sustainedload is closely related to the stress at which cracks developin the concrete paste. These are unstable cracks that can growunder a sustained stress. Thus, the 24-hour sustained load,,,-`-`,,`,,`,`,,`---


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duration is used to verify that the concrete is not stressed tooclose to its ultimate strength. In addition, successfullyholding a test load for 24 hours has a very positive effect onthe level of comfort in those who will use and occupy thestructure after the load test is completed. It is generallyunderstood, however, that this relatively brief load durationcannot demonstrate most time-dependent effects.

5.5.2 Stability at maximum load—Another approach hasrecently been introduced that significantly decreases theamount of time the maximum test load is sustained on atested structure. The reasons for the shorter duration ofsustained load are simple—economic implications and mini-mizing disruption for the building occupants—but the justi-fication for not holding the test load for an extended amountof time is complex. The idea is that by studying other behavioralcharacteristics of the tested member (that is, deviation fromlinearity, repeatability, and permanency), one can determineif the tested structure is approaching its ultimate strengthwithout maintaining the test load for a sustained duration.The drawback of the relatively shorter duration of loading isthat it does not create the same level of comfort as holdingthe load for 24 hours in those who will use the structure afterthe load test is completed. The level of experience with usinga shorter duration cyclic test is limited, and additional dataare needed to solidify the evaluation criteria.

5.6—Load testing procedureA variety of combinations of the aforementioned procedures

have been used over the last 100 years in international loadtesting practice. Two load test procedures are described inthe following sections. The first is the 24-hour monotonicuniform load test that has been used for many years and isprescribed by ACI 318. The second is the relatively newcyclic load test as discussed in Appendix A of ACI 437R.

5.6.1 Twenty-four-hour monotonic uniform load test—Once a structure has been selected to undergo a load test, apreliminary evaluation is conducted. The evaluation is meant todetermine, if possible, material and section properties,loading history, and levels of deterioration of the structure.Because the test load is applied in a uniformly distributedmanner similar to the design load pattern, certain characteristicsof the structure may or may not be investigated. When severaladjacent spans or bays are simultaneously loaded, charac-teristics, such as load sharing and fixity of supports, need notbe fully understood before the load test begins because thestructure will behave just as it would under design loading,and its ability to hold the design load will be determineddirectly by the load test. Preliminary calculations are typicallydone to determine some anticipated results; however,without fully understanding the structure’s behavior, thesecalculations are used only as a rough guide as to how thestructure will perform under the test loads and to locateinstrumentation to determine maximum responses during thetest. Once the structure is adequately instrumented at thelocations where the maximum response is expected, initialvalues of each instrument are recorded not more than 1 hourbefore application of the first load increment. After the test isstarted, the uniformly distributed load is applied in not less

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than four approximately equal increments. If the measurementsare not recorded continuously, a set of response readings aretaken at each of the four load increments until the total testload has been reached and again after the test load has beenapplied on the structure for at least 24 hours. Once the lastreadings under sustained load have been taken, the test loadis removed, and a set of final readings is taken 24 hours afterthe test load is removed. The measured deflections anddeflection recovery are compared with code-specifiedacceptance criteria (Table B.1 and Section 6.1). In case the
structure does not meet the acceptance criteria, Chapter 20 ofACI 318-05 allows the test to be repeated 72 hours after theremoval of the first test load.
This test method takes advantage of one very importantfactor in load testing—consideration of how load is distributedin the structure. Because the load is applied in the samepattern as designed, factors such as load sharing and endfixity are inherently considered during the load test and thusdo not require a full understanding of their contributions tothe overall strength of the structure. By demonstrating thatthe structure can sustain the applied design load for a 24-hourperiod without deflection or permanent deformationexceeding the preset limits, the results of the load test arerelatively straightforward. This method, however, does havesome drawbacks. The application of a uniformly distributedload can be time consuming and laborious. The overallduration of the test is at least 3 days (half a day to set up,24 hours at maximum load, 24 hours unloaded, and half aday to disassemble), assuming that retesting is not necessary.This amount of time with a continuous presence on a job siteis costly to an owner as well as disruptive to the tenants.Testing large areas of a structure or performing multiple testswithin a structure may be too time consuming and expensiveto provide a thorough evaluation of the overall performanceof the entire structure under design loads.

5.6.2 Cyclic load test—Appendix A of the ACI 437R-03reports the protocol for conducting a cyclic load test.

Following the preliminary investigation, the initial stepsfor planning a cyclic load test include structural analysis andload intensity definitions, which require considerable engi-neering effort as compared with the 24-hour monotonicuniform load test described previously. The predeterminedtest load is applied to discrete areas on the tested memberthat have been selected to maximize specific responses thatare being investigated in the member. To determine therequired magnitude, quantity, and location of appliedconcentrated loads, one must have a thorough understandingof the structure’s behavioral characteristics, including theeffects of load sharing and end fixity. These normally cannotbe accurately determined with simple hand calculations.Relatively complex models may be required to fullyunderstand the structural responses to the applied test loads.

The procedure of a cyclic load test consists of the applicationof concentrated loads in a quasi-static manner (that is,sufficiently slow to avoid strain rate effect) to the structuralmember in at least six loading/unloading cycles. Eventhough the number of cycles and the number of steps withineach cycle (five loading plus five unloading) should be--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---


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CHAPTER 6—ACCEPTANCE CRITERIA

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6.1—Criteria for 24-hour monotonic load testSection 20.5 of ACI 318-05 defines acceptance criteria for

interpreting the results of the 24-hour monotonic load test.The evaluation of the member/structure is based on two

different sets of acceptance criteria to certify whether or notthe load test is passed: a set of visual parameters (such as nospalling or crushing of compressed concrete is evident), andthe measured maximum deflections (must satisfy one of thefollowing two equations)

(6-1)

(6-2)

Defining an acceptable deflection criterion by the formulagiven in Eq. (6-1) makes it difficult to establish a relationshipwith typical deflection limits such as lt /240, lt/360, and soon. Also, the theoretical basis for Eq. (6-1), as discussed inChapter 3, is unrelated to modern material strengths,deflection limits, degree of fixity that may be present in thestructural member being tested, and current reinforcedconcrete construction practice. Most members/structurespass the acceptance criteria of the current monotonic loadtest, showing very small deflections.

Δmaxlt2

20,000h-------------------≤

Δr maxΔmax

4-----------≤

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considered as minimum requirements, in most cases theyprovide for an adequate assessment of structural perfor-mance. For this minimum test protocol, the total load testduration should be approximately 2 hours, with eachloading/unloading cycle lasting approximately 20 minutes.With reference to Fig. 5.1, the protocol description is givenas follows:• Benchmark—The initial reading of the instrumentation

should be taken no more than 30 minutes beforebeginning the load test and any load being applied.

• Cycle A—The first load cycle consists of five loadsteps, each increased by no more than 10% of the totaltest load expected in the cyclic load test. The load isincreased in steps, typically until the service level of themember is reached, but no more than 50% of the totaltest load. The maximum load level for each cycleshould be maintained until the structural responseparameters have stabilized.* During each unloadingphase (using similar steps as the loading phase), aminimum load Pmin of at least 10% of the total test loadshould be maintained to keep the test devices engaged.Response measurements are taken during both theloading and the unloading phases. The duration of acomplete loading/unloading cycle is set to a minimum of20 minutes, which implies that each loading/unloadingstep including the sustained phase is 2 minutes long;

• Cycle B—A repeat of Cycle A that provides a check ofthe repeatability of the structural response parametersobtained in the first cycle. Monitoring the repeatabilityof load-deflection response is of relevance at any loadlevel, including the relatively lower load Cycles A andC. For example, this allows the engineer to determine ifa change in stiffness (that greatly affects linearity) is theresult of cracking within the elastic range of themember;

• Cycles C and D—Load Cycles C and D are identical inload magnitude and achieve a maximum load level thatis typically halfway between the maximum load levelachieved in Cycle A and B and 100% of the total testload. The loading procedure is similar to that of Cycle Aand B. For Cycle C and D, it is suggested that the loadof the first of five steps be at the load level of the thirdstep of Cycle A, and the load of the second step be atthe level of maximum load attained in Cycle A. Theremaining three steps should be of equal magnitude toattain the maximum load level for Cycles C and D;

• Cycles E and F—The fifth and sixth load cycles, E andF, respectively, should be identical in load magnitude,and they should reach the total test load. For Cycles Eand F, it is suggested that the load of the first of fivesteps be at the load level of the third step of Cycle C,and the load of the second step be at the level ofmaximum load attained in Cycle C. The remaining

*For each load cycle, maximum load level needs to remain approximately constantfor at least 2 minutes. During this time interval, the measurands, such as deflection orstrain, have to remain stable before proceeding with unloading. Stability is definedherein as a change in the measurable not exceeding 5% of the initial value over aperiod of 2 minutes.

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three steps should be of equal magnitude to attain themaximum load level for Cycle E and F; and

• Final step—At the conclusion of Cycle F, the test loadshould be decreased to zero. A final reading should betaken no sooner than 2 minutes after the total test load,not including the equipment used to apply the load, hasbeen removed.

The main differences between the two protocols is that, forthe latter, the loads are applied in loading-unloading cyclesof increasing magnitude using hydraulic jacks, and themaximum test load is maintained for a shorter duration oftime. Using a sequence of loading and unloading cycles upto the predetermined maximum load level allows the engineera real-time assessment of member performance. The loadsequence is intended to identify, in an explicit manner, anyundesirable response. The response can be characterized bymonitoring parameters such as linearity of structural deflectionresponse, repeatability of load-deflection response, andpermanency of deflections (Chapter 6). An additionaladvantage is that the duration of the maximum applied loadin the cyclic load test may be considerably reduced from thatof the 24-hour monotonic uniform load test describedpreviously, which has economic implications and minimizesdisruption for the building occupants. The main drawbackswith the cyclic load-testing method are the amount ofengineering that is required to properly determine theappropriate test loads and the relatively small amount ofsupporting data used to determine evaluation criteria.

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Fig. 6.1—Example of load-versus-deflection curve for twocycles at same load level.

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Chapter 20 of ACI 318-05 requires that response measure-ments are to be made after each load increment is applied aswell as after the total load has been on the structure for atleast 24 hours. No commentary, however, is offeredregarding the purpose of the intermediate deflection readings.These measurements clearly provide an opportunity to verifythe linear response of the structure and to discontinue the testif a pronounced change in linearity is noted, as evidenced bya large increase in deflection observed after a loadingincrement. The concept of “deviation from linearity,”discussed in more detail in the following section, could beapplied to the intermediate readings of the 24-hour monotonicload test and provide an explicit guideline for interpretationof deflection readings taken during the sequence of loadapplication steps.

Chapter 20 of ACI 318-05 does not define acceptancecriteria for establishing satisfactory behavior at service loadlevel. Even though it is recognized that calculationsregarding deflection and crack width may not be sufficientlydeveloped or accurate to justify using them as mandatoryaccept/reject criteria at this load level, the engineer shouldinclude the assessment under service load as an integral partof the structural performance evaluation process.

In summary, new deflection acceptance criteria must bedeveloped. These deflection acceptance criteria shouldgenerally be based on the following principles of engineeringmechanics under the assumption that accurate deflectionreadings are attained:• Maximum deflection under full test load compared

with calculated theoretical maximum deflection at thatload level;

• Recovery of deflection upon full removal of load; and• Linearity of deflection response during loading and

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6.2—Criteria for cyclic load testAppendix A of ACI 437R-03 describes the cyclic load test

method. This alternative load test method appears to offersome advantages in terms of reliability and understanding ofstructural response to load. Three distinct measures ofperformance are proposed for the cyclic load test method(CLT method): repeatability, permanency (that is related todeflection recovery), and deviation from linearity. Theacceptance criteria are based on limited testing as describedin Chapter 3 of this report. The three criteria may be relatedto any response (for example, deflection, rotation, and strain);however, deflection appears to be the most convenient (CIAS2000). As such, performance measures and acceptance criteriaare described in this section in terms of deflection.• Repeatability is a measure of the similarity of behavior

of the member/structure during two twin load cycles(Fig. 6.1) at the same load level, and is calculatedaccording to the following equation

IR = repeatability index = × 100% (6-3)

Repeatability as defined herein is not an indicator of thequality of the testing technique, but rather an indicatorof structural performance related to recoverable (elastic)deflection and load-deflection response in general. Experi-ence (Mettemeyer 1999) has shown that a repeatabilityindex IR in the range of 95 to 105% is a satisfactory. Forvalues of IR inside this range, the member/structure canbe considered to pass the load test;

• Permanency is the relative value of the residual deflec-tion compared with the corresponding maximum deflec-tion during the second of two twin load cycles at thesame load level. It should be less than 10% (Mettemeyer1999) for the member/structure to be considered passingthe load test. The permanency index IP is computedusing the following equation (Fig. 6.1, Cycle B)

IP = permanency index = × 100% (6-4)

If the level of permanency is higher than the aforemen-tioned 10%, it may be an indication that load applicationhas damaged the member/structure and that nonlineareffects are taking place; and

• Deviation from linearity represents the measure of thenonlinear behavior of a member/structure being testedat any time after a given threshold that typically corre-sponds to its service load level. To define deviationfrom linearity, linearity is defined first as the ratio ofthe slopes of two secant lines intersecting the load-deflection envelope (Fig. 6.2). Figure 6.2 shows theschematic load-deflection curves obtained by a total ofsix loading cycles (A through F), which consisted ofthree pairs of twin cycles with each pair at the sameload level. The load-deflection envelope is the curve

ΔmaxB Δr

B–

ΔmaxA Δr

A–------------------------

ΔrB

ΔmaxB

-----------


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Fig. 6.2—Schematic load-versus-deflection curve for sixcycles.

constructed by connecting the points corresponding toonly those loads that are greater than or equal to anypreviously applied load. As expressed by Eq. (6-5), the

Linearityi = × 100% (6-5)αi( )tan

αref( )tan----------------------

linearity of any point i on the load-deflection envelopeis the percent ratio of the slope of the secant line* topoint i, expressed by tan(αi), to the slope of the refer-ence secant line,† expressed by tan(αref)

The deviation from linearity of any point i on the load-deflection envelope is the complement of the linearity ofthat point, as given in the following equation

IDL = deviation from Linearityi index = 100% – Linearityi (6-6)

Once the level of load corresponding to the referencepoint has been achieved, deviation from linearity shouldbe monitored continuously until the conclusion of thecyclic load test. Experience (Mettemeyer 1999) hasshown that IDL values less than 25% indicate that thestructure has passed the load test.

If a member/structure is initially uncracked and becomescracked during the load test, the change in flexuralstiffness as a result of a drastic change in moment ofinertia at the crack location(s) can produce a very highdeviation from linearity that is not necessarily related todegradation in strength (Masetti 2005). For such amember/structure, repeatability and permanency maybe better indicators of damage occurrence, or IDL shouldbe only computed for the member/structure undercracked conditions.

While additional research and field testing of structuresare required to verify the overall suitability of the CLTmethod, adoption of these measures of performance and therecommended threshold levels appear justifiable.

6.2.1 Determination of member/structure capacity (loadrating)—The cyclic load test could also be used to determinethe capacity of a given member/structure based on the three-index acceptance criteria if the load test is not terminatedwhen the TLM level is reached (Casadei 2004). In fact, asreal-time measurements and assessment are possible, theengineer can apply a number of twin load cycles atincreasing load levels until one of the three acceptancecriteria fails (that is, attainment of the critical load). Giventhe critical load and after subtracting the factored dead load,the engineer can establish the safe live load level. Thevalidity of this load rating protocol rests on the reliability ofthe acceptance criteria and their threshold values to correctlypredict the necessary strength reserve in the structure.

*Secant is the line that connects the origin to the point of interest on the load-deflectionenvelope.

†The reference point usually coincides with the peak load of the first cycle.

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6.3—Considerations of performance assessment at service load level

Irrespective of the loading procedure (that is, monotonicor cyclic load) and type of load (that is, uniformly distributedload over the entire tributary area, strip load, or patch load(s)),measurements of flexural deflection and crack spacing andwidth under the test load equivalent to the service condition(that is, 1.0Dw + 1.0Ds + 1.0L) should be recorded andchecked against limit values established by the engineer.

When applicable, if the measured deflection or crackwidth exceed their respective limits set by the engineer,careful consideration should be given to continuing the loadtest to higher load levels. It is recognized that the variablenature of cracking and the challenges in accurately measuringand predicting crack width make the corresponding limitsdifficult to implement. The intent of the provision, however,is to caution the engineer that the occurrence or growth ofexcessive cracks under “immediate” service loads may be asignal of structural deficiencies. Influence of crack width isof particular significance for some members/structures, suchas those exposed to aggressive environments. If crack widthsfor watertight structures or those exposed to aggressiveenvironments exceed the preset limits, the structure need notbe considered to have failed the load test with respect to safety.Provided that the structure meets the requirements forperformance under full TLM, it may still be consideredsatisfactory if additional protective measures can be taken toprevent or retard future deterioration.

Guidance for establishing possible limit values for deflectionand crack width at service load are as follows:• Maximum measured deflection should not exceed the

permissible values given in Table 9.5(b) of ACI 318-05Chapter 9 for the various types of members. This criterion

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is only applicable if the load distribution patternreflects the one used for design, which is typically notthe case for test loads of the strip or patch type. Further-more, the first two values in Table 9.5(b) are intendedfor immediate live load deflections, while the third andfourth deflection limits are for the additional deflectionoccurring after attachment of nonstructural membersdue to long-term deflection caused by all sustainedloads plus any immediate live load deflection. Thismakes these limits difficult to apply in the setting of aload test where only the immediate deflection due toapplied loads can be measured. Long-term deflectiondue to sustained loads can be calculated and then addedto the load test deflection results for live loading toarrive at a value that can be compared with the lattertwo limits of Table 9.5(b); and

• The maximum width of new flexural cracks formedduring the course of the load test or the change in widthof existing flexural cracks should not exceed a limitingwidth determined by the engineer, owner, or buildingofficial before the load test. Consideration should begiven to the intended use and exposure conditions forthe structure or member. Limiting crack widths shouldbe selected based on the following:

1. Suggested tolerable crack widths as reported by ACICommittee 224 (ACI 224R); and

2. The value of the analytical width computed as theproduct s times Δεs, where s is the average spacingbetween cracks, and Δεs represents the difference instrain in the longitudinal steel reinforcement when thecross section of interest is considered cracked anduncracked, respectively, and subject to an appliedmoment at that location resulting from the service load.

6.4—Recommendations for acceptance criteria at test load magnitude level

Adoption of the acceptance criteria for both monotonicand cyclic load tests is recommended as described in thefollowing sections. In contrast to service condition, acceptancecriteria at the TLM level are mandatory pass-fail requirementsand are established based on the load procedure adopted(that is, monotonic or cyclic load).

6.4.1 Twenty-four-hour monotonic load test procedure—The acceptance criteria listed as follows need to be checked:

1. While increasing the load from service to TLM andwhile holding the maximum load constant for 24 hours, thestructure should show no signs of impending failure, such asconcrete crushing in the compressive zone or concretecracking exceeding a preset limit. This criterion is of a qual-itative nature;

2. The maximum absolute deflection recorded at the 24thhour of sustained TLM should be less than the memberdeflection computed analytically in accordance withSections 9.5.2.2 through 9.5.2.5 of ACI 318-05. This criterionrequires that the engineer carefully considers the loaddistribution pattern during computations. It is recognized

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that a load test is typically undertaken when insufficientinformation is available to perform a strictly analyticalevaluation. The objective of this provision is to make surethat the engineer has made a prediction, given the availableinformation and that such prediction be used to interpret theexperimental results. There should be an upper limit to themeasured absolute deflection that, if exceeded, rules out theoption of using deflection recovery as an acceptance criterionas well as retesting. Such a limit is suggested to be equal tolt /180; and

3. The residual deflection of the member should be lessthan 25% of the corresponding absolute maximum deflec-tion immediately upon unloading or 24 hours afterward,respectively.

a. If the member/structure is sufficiently stiff, deflectionrecovery is not relevant. In fact, it may even beunfeasible to compute the deflection recovery due tolimitations in the precision/accuracy of the deflectionmeasurement equipment. No check on deflectionrecovery is required if the absolute deflection is lowerthan 0.05 in. (1.3 mm) or the deflection as apercentage of span length is less than lt /2000; and

b. If the member/structure fails the deflection recoverycriterion on the first test, retesting should bepermitted, with the stipulation that the engineer estab-lishes that deflection does not represent a service-ability problem. An upper limit on residual deflectionafter the retest equal to 10% of the maximum deflectionrecorded during the retest is recommended.

If any one of the three aforementioned criteria listed is notmet, the member/structure should be considered havingfailed the load test. No retesting is permitted except for thestipulation in Item 3.

6.4.2 Cyclic load test procedure—The following acceptancecriteria need to be checked:

1. While increasing the load from service to TLM and anytime during the load test, the structure should show no signsof impending failure, such as concrete crushing in thecompressive zone or concrete cracking exceeding a presetlimit. This criterion is of a qualitative nature;

2. The maximum deflection recorded at the second loadcycle that reaches TLM should be less than the memberdeflection computed analytically in accordance withSections 9.5.2.2 through 9.5.2.5 of ACI 318-05. This crite-rion requires that the engineer carefully considers the loaddistribution pattern during computations. It is recognizedthat a load test is typically undertaken when insufficientinformation is available to perform a strictly analyticalevaluation. The objective of this provision is to make surethat the engineer has made a prediction given the availableinformation and that such a prediction be used to interpretthe experimental results;

3. The repeatability index IR, a measure of the similarity ofbehavior of the member/structure during two equal-levelload cycles, should never be outside the range of 95 to 105%;

4. The deviation from linearity index IDLi , a measure ofthe nonlinear behavior of the member/structure beingtested, should be monitored continuously during the cyclic

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load test until its conclusion, and never exceed thethreshold value of 25%. Special consideration should begiven to a structure/member that cracks during the load testif cracking is not considered detrimental to the service-ability of the structure; and

5. The permanency index IP, the relative value of the residualdeflection compared with the corresponding maximumdeflection during the second of two equal-level twin loadcycles, should never exceed the threshold value of 10%.

If any one of the five aforementioned criteria listed is notmet, the member/structure should be considered havingfailed the load test intended to reach the selected TLM. Noretesting is permitted.

6.5—Strength reserve beyond load test acceptance criteria

Irrespective of the test method, it is important to under-stand the strength reserve that likely remains in the member/structure after it passes the load test.

Results from load tests conducted on five different structuresusing either the 24-hour monotonic load test or the cyclicload test followed by loading to failure were used to establishthreshold values for repeatability, permanency, and deviationfrom linearity (Mettemeyer 1999). These threshold valueswere set at limits that would ensure some reserve capacity inthe member once one of the threshold values was surpassed.Because the structures were loaded monotonically up tofailure, after the 24-hour or cyclic load tests were concluded,the only criterion that could be calculated up to failure wasdeviation from linearity. A threshold value of 25% fordeviation from linearity was set because it allowed for atleast a 40% strength reserve in the members before collapse.The threshold values for repeatability and permanency wereselected based on the extreme values experienced during the24-hour and cyclic load tests conducted on the five members.

Additional work (Casadei et al. 2005) on nearly identicalreinforced concrete one-way slabs that were loaded to ultimatefailure allowed for the determination of the strength reservebefore collapse after the slabs had failed either the 24-hourmonotonic or the cyclic load test. The criterion that becamecritical during the load tests was deviation from linearity. Inthis project, the margin of safety (that is, strength reserve)with respect to ultimate failure was found to be approximately20% of the maximum load applied during the test for all slabsthat also collapsed with the same failure mode. Obviously, alarge database including different construction systems andstructural configurations would be necessary to arrive atmore definite conclusions.

CHAPTER 7—SUMMARYThe TLM and acceptance criteria as currently defined in

Chapter 20 of ACI 318-05 should be revised. The purpose of revising the TLM is twofold. The first

purpose is to define a test load that demonstrates an acceptable,safe margin of capacity over design service dead and liveload levels and to be as consistent as possible, regardless ofthe self-weight of the structure or the code used for theoriginal design. The proposed TLM puts more emphasis on

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the variable portions of the service loads (the live loads andsuperimposed dead loads) and in so doing provides a moreconsistent proof load than does the ACI 318-05. Second, therecommended equations given in Chapter 4 of this report todefine the test load magnitude are parallel with the equationsfor required strength given in Chapter 9 of ACI 318-05 andso provide a consistent format and logic within the code.

While the 24-hour monotonic load test has been part of theACI code since the early part of the last century, it isrecommended that the cyclic load test method described inChapter 5 be considered for use in the code to supplement thecurrent test method. The cyclic method provides a techniqueto more thoroughly evaluate structural response than doesthe monotonic load test method.

The current maximum deflection and deflection recoverycriteria need to be revised because the theoretical bases forthe criteria are considered inapplicable to most structuralsystems and modern materials, and are unrelated to designcriteria. A clearer rationale and explanation of deflectioncriteria have been provided in Chapter 6 of this report. Forperformance assessment at service load levels, the proposeddeflection limits for evaluating test results are related to thedeflection limits of Chapter 9 of ACI 318-05, and for the24-hour monotonic load test protocol, the predicted deflectionused to establish an acceptable upper bound is to be calculatedusing the deflection prediction equations of Chapter 9. Thisconsistency within the code would dispel some of themystery associated with the current deflection limit for loadtesting. An additional set of acceptance criteria has beenproposed when cyclic load testing is used. Additionaltesting and verification of the appropriate values foracceptance criteria for cyclic load testing are needed to makethe test interpretation more meaningful.

As discussed in Chapter 4, this report recommends that theTLM be redefined in terms of service loads rather thanrequired strength; however, there is the acknowledgementthat the intent of the new definition is to limit the test load toapproximately 85 to 90% of the required strength as definedin ACI 318-05 when testing all suspect areas of a structure,or 90 to 95% of the required strength when testing only aportion of the suspect areas. The load test provisions inChapter 20 of ACI 318-05 should be reviewed any time thereis a change in the definition of required strength, strength-reduction factors (φ-factors), or both.

This report uses as a reference the provisions on loadtesting outlined in ACI 318-05, and will have to be modifiedif future editions of the building code change such provi-sions. From a legal standpoint, ACI 318 sets the bindingrequirements. The recommendations provided in this reporthave the purpose of integrating and enriching the under-standing and practice of load testing and its acceptancecriteria, but do not replace ACI 318 provisions.

CHAPTER 8—REFERENCES8.1—Referenced standards and reports

The documents of the various standards-producing organi-zations referred to in this document are listed with their serialdesignations. Because some of these documents are revised

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frequently, the user of this report should check for the mostrecent version.

American Concrete Institute (ACI)224R Control of Cracking in Concrete Structures 318 Building Code Requirements for Structural

Concrete and Commentary437R Strength Evaluation of Existing Concrete Buildings

ASTM InternationalE 196 Standard Practice for Gravity Load Testing of

Floors and Low Slope RoofsF 914 Standard Test Method for Acoustic Emission for

Insulated and Non-Insulated Aerial PersonnelDevices Without Supplemental Load HandlingAttachments

International Code CouncilInternational Building Code (IBC)

8.2—Cited referencesACI Committee 318, 1947, “Building Code Requirements

for Reinforced Concrete (ACI 318-47),” American ConcreteInstitute, Farmington Hills, Mich., 64 pp.

ACI Committee 318, 1951, “Building Code Requirementsfor Reinforced Concrete (ACI 318-51),” ACI JOURNAL,Proceedings V. 47, No. 8, Apr., pp. 589-652.

ACI Committee 318, 1956, “Building Code Requirementsfor Reinforced Concrete (ACI 318-56),” ACI JOURNAL,Proceedings V. 52, No. 9, May, pp. 913-986.

ACI Committee 318, 1963, “Building Code Requirementsfor Reinforced Concrete (ACI 318-63),” American ConcreteInstitute, Farmington Hills, Mich., 144 pp.

ACI Committee 318, 1971, “Building Code Requirementsfor Reinforced Concrete (ACI 318-71),” American ConcreteInstitute, Farmington Hills, Mich., 78 pp.

ACI Committee 318, 1999, “Building Code Requirementsfor Structural Concrete (ACI 318-99) and Commentary(318R-99),” American Concrete Institute, Farmington Hills,Mich., 391 pp.



ACI Committee 437, 1967, “Strength Evaluation ofExisting Concrete Buildings (ACI 437R-67),” AmericanConcrete Institute, Farmington Hills, Mich., 6 pp.

ACI Committee 437, 1982, “Strength Evaluation ofExisting Concrete Buildings (ACI 437R-67) (Revised1982),” American Concrete Institute, Farmington Hills,Mich., 7 pp.

ACI Committee 437, 2003, “Strength Evaluation ofExisting Concrete Buildings (ACI 437R-03),” AmericanConcrete Institute, Farmington Hills, Mich., 28 pp.

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ACI Committee E-1, 1928, “Joint Code Building Regula-tions for Reinforced Concrete,” Report on ReinforcedConcrete Building Design and Specifications Amended andAdopted as a Tentative Standard at the Twenty-Fourth AnnualConvention of the American Concrete Institute, Feb. 28.

American Concrete Institute, 1920, “Standard Specifica-tion No. 23—Standard Building Regulations for the Use ofReinforced Concrete,” American Concrete Institute, Farm-ington Hills, Mich.

American Concrete Institute, 1936, “Building Code Regu-lations for Reinforced Concrete,” ACI 501-36T, AmericanConcrete Institute, Farmington Hills, Mich.

American Society of Civil Engineers (ASCE), 2002,“Minimum Design Loads for Buildings and Other Struc-tures,” ASCE, Reston, Va. (CD-ROM)

American Society of Mechanical Engineers (ASME),2005, “Reinforced Thermoset Plastic Corrosion ResistantEquipment,” ASME, New York, 340 pp.

American Society of Mechanical Engineers (ASME),2004, “BPVC Section X—Fiber-Reinforced Plastic PressureVessels,” ASME, New York.

Arnan, M. A.; Reiner, M.; and Teinowitz, M., 1950,“Research on Loading Tests of Reinforced Concrete Struc-tures,” Report, Standards Institution of Israel, Jerusalem, 52 pp.

Bares, R., and FitzSimons, N., 1975, “Load Tests ofBuilding Structures,” Journal of the Structural Division,ASCE, May, pp. 1111-1123.

Birkmire, W. H., 1894, Skeleton Construction in Buildings,John Wiley & Sons, New York, 80 pp.

BRE Information Paper 2/95, 1995, “Guidance for EngineersConducting Static Load Tests on Building Structures,”Building Research Establishment, England, 4 pp.

Canadian Standards Association, 1994, “Design ofConcrete Structures, Chapter 20—Strength EvaluationProcedures,” Standard A23.3.

Casadei, P., 2004, “Assessment and Improvement ofCapacity of Concrete Members: A Case for In-Situ LoadTesting and Composite Materials” PhD dissertation, Depart-ment of Architecture and Civil Engineering, University ofMissouri-Rolla, Rolla, Mo.

Casadei, P.; Parretti, R.; Heinze, T.; and Nanni, A., 2005,“In-Situ Load Testing of Parking Garage RC Slabs: Compar-ison Between Cyclic and 24 Hrs Load Testing,” PracticePeriodical on Structural Design and Construction, ASCE,V. 10, No. 1, Feb., pp. 40-48.

Chicago Building Ordinance, 1910.Committee on Reinforced Concrete and Building Laws,

1916, “Proposed Revised Standards Building Regulationsfor the Use of Reinforced Concrete,” Proceedings of theTwelfth Annual Convention of the American ConcreteInstitute, p. 172.

Committee on Reinforced Concrete and Buildings Laws,1917, “Proposed Standard Building Regulation for the Use ofReinforced Concrete,” Proceedings of the Thirteenth AnnualConvention of the American Concrete Institute, p. 410.

Concrete Innovation Appraisal Service (CIAS), 2000,“Guidelines for the Rapid Load Testing of Concrete Struc-


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APPENDIX A—DETERMINATION OFEQUIVALENT PATCH LOAD

tural Members,” CIAS Report 00-1, American ConcreteInstitute, Farmington Hills, Mich., 97 pp.

Condron, T. L., 1917, “Principles of Design and Results ofTests on Girderless Floor Construction of ReinforcedConcrete,” Proceedings of the Ninth Annual Convention ofthe National Association of Cement Users, pp. 116-126.

Czechoslovak State Standard CSN 73 2030, 1977,“Loading Tests of Building Structures, Common Regula-tions,” Publishers for the Office for Standardization andMeasurement, Prague, Czechoslovakia, p. 38.

FitzSimons, N., and Longinow, A., 1975, “Guidance forLoad Tests of Buildings,” Journal of the Structural Division,ASCE, pp. 1367-1380.

Galati, N.; Casadei, P.; Lopez, A.; and Nanni, A., 2004,“Load Test Evaluation of Augspurger Ramp ParkingGarage, Buffalo, NY,” Report 04-50, University ofMissouri-Rolla, Rolla, Mo.

Genel, M., 1955a, “Ripartizione Laterale dei Carichi inSeguito alla Monoliticita’ del Cemento Armato,” IlCemento, V. 52, June, pp. 6-15.

Genel, M., 1955b, “Ripartizione Laterale dei Carichi inSeguito alla Monoliticita’ del Cemento Armato (continu-azione),” Il Cemento, V. 52, July, pp. 6-13.

Hennebique, F., 1909, Ferro-Concrete Theory and Prac-tice, A Handbook for Engineers and Architects, L. G.Mouchel & Partners, Ltd., London, 359 pp.

Institution of Structural Engineers, 1964, “Report of aCommittee on the Testing of Structures,” London, 24 pp.

International Code Council, 2003, International BuildingCode, International Code Council, Inc., 358 pp.

Japanese Society for Nondestructive Inspection (JSNDI),1991, “Methods for Absolute Calibration of Acoustic Emis-sion Transducers by Reciprocity Technique,” NDIS 2109.

Japanese Society for Nondestructive Inspection (JSNDI),1997, “Evaluation of Performance Characteristics ofAcoustic Emission Testing Equipment,” NDIS 2106.

Japanese Society for Nondestructive Inspection (JSNDI),1997, “Evaluation Method for the Deterioration of AcousticEmission Sensor Sensitivity,” NDIS 2110.

Japanese Society for Nondestructive Inspection (JSNDI),1997, “Recommended Practice for the Continuous AcousticEmission Monitoring of Pressure Vessels,” NDIS 2419.

Japanese Society for Nondestructive Inspection (JSNDI),2000, “Recommended Practice for In-Situ Monitoring ofConcrete Structures by Acoustic Emission,” NDIS 2421, 6 pp.

Joint Committee on Concrete and Reinforced Concrete,1913, “Second Report of Joint Committee on Concrete andReinforced Concrete,” 1913 Proceedings of the AmericanSociety of Civil Engineers, 45 pp.

Kramer, E. W., and Raafat, A. A., 1961, “The WardHouse: a Pioneer Structure of Reinforced Concrete,” Journalof the Society of Architectural Historians, V. 20, No. 1, Mar.,pp. 34-37.

Lombardo, S., and Mirabella, G., 2004, “Il CollaudoTecnico Amministrativo dei Lavori Pubblici” Dario Flac-covio Editore s.r.l. (in Italian)

Masetti, F., 2005, “Structural Implications of Field LoadTesting Using Patch-Loads,” MS dissertation, Department

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of Architecture and Civil Engineering, University ofMissouri-Rolla, Rolla, Mo.

Masetti, F.; Galati, N.; Nehil, T.; and Nanni, A., 2006, “In-Situ Load Test: a Case Study,” Paper 16-9, fib SecondCongress, June 4-8, Naples, Italy, 11 pp. (CD-ROM)

Mettemeyer, M., 1999, “In Situ Rapid Load Testing ofConcrete Structures,” Master’s thesis, Department of CivilEngineering, University of Missouri-Rolla, Rolla, Mo.

National Association of Cement Users (NACU), 1908,“Report of the Committee on Laws and Ordinances,”National Association of Cement Users, pp. 233-239.

National Association of Cement Users (NACU), 1910,“Standard Building Regulations for the Use of ReinforcedConcrete,” NACU Standard No. 4, National Association ofCement Users, pp. 349-361.

Nehil, T.; Masetti, F.; and Nanni, A., 2006, “Test LoadMagnitude and Acceptance Criteria For Strength Evaluationby Means of Load Testing: Current Recommendations ofAmerican Concrete Institute Committee 437—StrengthEvaluation,” Paper 16-24, fib Second Congress, June 4-8,Naples, Italy, 9 pp. (CD-ROM)

Perrot, E. G., 1911, “Analysis of Results of Load Test onPanels of Reinforced Concrete Buildings,” Proceedings ofthe Seventh Annual Convention of the National Associationof Cement Users, p. 216.

RILEM, 1980, “General Recommendation for Statical LoadTest of Load-Bearing Concrete Structure In Situ,” TBS-2.

Slater, W. S., 1912, “The Testing of ReinforcedConcrete Buildings Under Load,” Proceedings of theEighth Annual Convention of the National Association ofCement Users, p. 165.

Turner, C. A. P., 1912, Examples of the Mushroom Systemof Reinforced Concrete Construction, 68 pp.

Urquhart, L. C., and O’Rourke, C. E., 1926, Design ofConcrete Structures, McGraw-Hill, New York, 482 pp.

Vatovec, M.; Kelley, P.; Alkhrdaji, T.; and Nanni, A.,2002, “Evaluation and Carbon Fiber Reinforced PolymerStrengthening of an Existing Garage: Case Study,” Journalof Composites for Construction, V. 6, No. 3, pp. 184-193.

Wright, F. L., 1906, “Specifications for the Constructionof Unity Temple,” 38 pp.

A.1—NotationThe selection of notations reported in this section only

refers to the symbols used in this appendix.a = dimension of patch load in longitudinal direction,

in. (mm)b = dimension of patch load in transverse direction,

in. (mm)c = comprehensive coefficient for determination of

equivalent test loadc1 = coefficient for determination of equivalent test

load, longitudinal directionc2 = coefficient for determination of equivalent test

load, transverse directionE = concrete modulus of elasticity, psi (N/mm2)


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Is = moment of inertia of slab, in.4 (mm4)ks1 = rotational stiffness at left span-end location, kip-

ft (kN-m)ks2 = rotational stiffness at right span-end location, kip-

ft (kN-m)Ll = slab span in longitudinal direction, ft (m)Lt = slab span in transverse direction, ft (m)Mint1 = moment at center-span for System 1 in Fig. A.3,

Fig. A.1—Loading configuration.

vr

kip-ft (kN-m)Mint2 = moment at center-span for System 2 in Fig. A.3,

kip-ft (kN-m)ML1 = moment at left span-end for System 1 in Fig. A.3,

kip-ft (kN-m)ML2 = moment at left span-end for System 2 in Fig. A.3,

kip-ft (kN-m)MR1 = moment at right span-end for System 1 in Fig. A.3,

kip-ft (kN-m)MR2 = moment at right span-end for System 2 in Fig. A.3,

kip-ft (kN-m)P = force corresponding to w x Ll x Lt , kip (kN)Ps = force corresponding to ws x a x b , kip (kN)t = slab thickness, in. (mm)v(x) = analytically computed deflected shape, in. (mm)w = magnitude of total uniformly distributed test load

(TLM), lb/ft2 (kN/m2)ws = magnitude of equivalent patch test load, lb/ft2

(kN/m2)wscal = magnitude of patch test load used to calibrate

coefficient c, lb/ft2 (kN/m2)x = coordinate along the longitudinal axis, in. (mm)

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A.2—IntroductionA 24-hour load test or a cyclic load test conducted with

hydraulic jacks that apply concentrated or patch loads (ws) asan alternative to the distributed load (TLM = w) offerssignificant advantages. A disadvantage is the computationalcomplexity associated with the determination of the patchload(s) that generates the internal forces (that is, shear orbending moment) at a critical location identical to that for thedistributed load.

This appendix intends to provide a concise explanation ofthe analytical steps necessary for the determination of wsgiven the value of w. To accomplish this objective, only theconcepts are presented, leaving the details to available literature(Masetti 2005; Masetti et al. 2006; Nehil et al. 2006) andusing as an example the case of a one-way slab (for whichthe positive moment at midspan is the force at the location ofinterest). Other cases can be approached using the methodologyshown.

A.3—One-way slab systemTo load-test a one-way reinforced concrete slab for positive

moment at midspan, a uniformly distributed test load, TLM= w, should be considered as shown in Fig. A.1(a). Theequivalent load test can be performed by applying the loadon a restricted area of the slab of interest. For example, theapplied load may consist of transverse or longitudinal loadstrips (Fig. A.1(b) and (c) or a patch load as shown inFig. A.1(d)). The equivalent test load ws , irrespective of thepattern, has to be selected to cause, at a given location, thesame internal force caused by w. The relationship betweenthe two load values is described by the following equation

ws = c1 × c2 × w = c × w (A-1)

where c, c1, and c2 are coefficients such that: c = c1 × c2 isgreater than 1.0.

The coefficient c1 depends on both the degree of fixity ofthe slab restraints at the main beam locations and the loadingstrip length a. Its value approaches 1.0 when the strip lengtha approaches the slab length Ll.

The coefficient c2 is a function of the transverse stiffnessof the slab; it reflects the fact that the portions of the slab towhich the load is not applied participate in the load sharing.The coefficient c2 increases with the decreasing of theloading strip width b and its value approaches 1.0 when thestrip width b approaches the slab width Lt.

The determination of the coefficient c = c1 × c2 is nottrivial, and several approaches can be adopted. In thefollowing sections, preliminary calculations and an experi-mental method for its refinement are described for a load testto be conducted with a patch load, as shown in Fig. A.1(d).

A.4—Procedure and preliminary calculationsThe engineer in charge of the load test must estimate ws in

advance, after the pattern of patch load application and themagnitude w have been established. It is important torecognize that any structural analysis must treat fixity andstiffness as preliminary assumptions that could be refinedbased on actual behavior once the structure is loaded and its,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---


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Table A.1—Numerical example: geometry and loads (Fig. A.1)Geometry Loads

Slab

Ll , ft (m) 16 (4.88) TLM w, lb/ft2 (kN/m2) 100 (4.79) P = w × Ll × Lt, kip (kN) 28.8 (128.11)

Lt, ft (m) 18 (5.49)

Preliminary

c1 6.25

t, in. (mm) 7 (177) c2 9.28

Beams, in. (mm) 18 x 24(457 x 610) ws, lb/ft2 (kN/m2) 5777 (276.60) Ps = ws × a × b, kip (kN) 8.67 (38.57)

Columns, in. (mm) 18 x 18(457 x 457) wscal, lb/ft2 (kN/m2) 575 (27.53)

Patch loada, in. (mm) 12 (305)

After calibrationcycle

c1 5.95

b, in. (mm) 18 (457) c2 7.83

ws, lb/ft2 (kN/m2) 4662 (223.22) Ps = ws × a × b, kip (kN) 7.01 (31.18)

i

response is measured. With these refinements, the inducedinternal forces can be determined with a much higher degreeof accuracy.

The preliminary analysis, given w and the patch-loadconfiguration, should consist of three main steps:

1. Estimate the stiffness of every structural member in thesystem (that is, columns and beams);

2. Perform a calculation of the critical internal force (thatis, positive moment) at the selected location due to w; and

3. Calculate ws using the target force and the degree offixity obtained from Steps 1 and 2.

The strength of the system subjected to ws should be checkedto ensure safety. For example, if the test is meant to produce acritical flexural response, the shear capacity of the structure is tobe checked to prevent shear failure. In addition, if memberswithin the structure are used to supply the reaction to ws, thecapacity of those members should be checked as well.

For the purpose of an example, a one-way reinforcedconcrete slab system with characteristics given in Table A.1is given (Fig. A.1(d)). First, a preliminary analysis isperformed to estimate ws, and then a real load cycle at apercentage of the estimated ws value allows for calibration.In the preliminary phase, the span-end fixities are estimatedfollowing the Commentary R13.7.4 of ACI 318-05, and thecoefficient c1 is calculated using traditional structuralanalysis methods imposing the patch load ws to produce the

Fig. A.2—LVDT locations.

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same maximum positive moment at center-span caused bythe uniformly distributed load w. The coefficient c2 iscalculated by means of the evaluation of the slab width thateffectively participates in sharing the load along the transversedirection (Genel 1955a,b). As shown in Table A.1, both c1and c2 assume values greater than one in the preliminaryphase because the load is applied by strips of width a and bsmaller than Ll and Lt. After the value ws is estimated, apretest cycle can be performed to refine the calculation of c1and c2. For the pretest, a load magnitude wscal = 10% ws isdeemed reasonable because the structure is linear elastic inthis range. Following the procedure described in SectionA.5, the values of c1 and c2 are recomputed and the finalvalue of ws is obtained, as shown in Table A.1.

A.5—Calculations after calibration cycleThe objective of this section is to show the procedure to

compute the values of c1 and c2 once a calibration cycle at amagnitude wscal has been performed. The load wscal shouldbe selected taking into consideration the following aspects:• It cannot exceed the linear elastic threshold of the

structure; and• It has to be large enough to cause a deflected shape to

be read with adequate accuracy by the sensors used inthe test setup.

The coefficients c1 and c2 are computed separately,making reference to the sketches of Fig. A.1(b) and (c). Incase of a patch load, the separation is only applicable if theprinciple of superposition is valid (elastic and linearbehavior). This separation is only for the purpose of thepresentation. In reality, because the structure is subject to apatch load instead of a strip load, c1 and c2 are interrelated.In the given example, seven sensors (linear variable differen-tial transducers [LVDTs]) were used along both the longitu-dinal and transverse directions (Fig. A.2 shows theirlocations), for a total of 13 devices.

A.5.1 Determination of c1—Referring to Fig. A.3, the loadws producing the same maximum positive moment inSystem 2 as produced by w in System 1 will be determined.The relationship between w and ws is expressed by

ws = c1w (A-2)

taken from Eq. (A-1), when c2 = 1.


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Fig. A.3—Structural models representing real slab.

ige

pr

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The procedure presented herein allows solving Eq. (A-2)using the experimentally determined value of c1 obtainedafter the calibration cycle.

Three simplifications are necessary to develop a manageablemodel. First, in Fig. A.3, the supports are assumed to bepoints, while in reality they have a finite width equal to thatof the main beams; second, ks1 and ks2 are the springs repre-senting the rotational stiffness of the slab connection to themain beams; and third, the structural system is assumed to belinear. Mint1 and Mint2 are the maximum positive moments,while ML1, MR1, ML2, and MR2 are the moments acting at thesupports in Systems 1 and 2 of Fig. A.3. For the structurespresented in Fig. A.3, considering linear elastic behavior, thefollowing equations can be obtained for System 1

(A-3)

and for System 2

(A-4)

To determine ws as a function of w, it is necessary toimpose that Mint1= Mint2, and solve for ws. The values of ks1and ks2 are unknown and need to be determined experimentallyby means of the preliminary test. The degree of fixity at theslab ends can be calculated by means of the procedureoutlined below consisting of eight sequential steps:

Step 1 A load wscal is applied using the load pattern of System 2, anddeflections are recorded at a number of locations given in Step 4.

Step 2 The moment diagram M(x) has the shape shown in Fig. A.3(b); itsvalues are unknown, but its equation has the following form:

(A-5)

where A, B, C, D, E, F, and G are constants that depend on a1, a2,and a; wscal; and ks1 and ks2.

ML1 ML1 w Ll E Is ks1 ks2, , , , ,( ) =

MR1 MR1 w Ll E Is ks1 ks2, , , , ,( ) =

Mint1 Mint1 w Ll E Is ks1 ks2, , , , ,( )=⎩⎪⎨⎪⎧

ML2 ML2 ws a1 a2 a E Is ks1 ks2, , , , , , ,( ) =

MR2 MR2 ws a1 a2 a E Is ks1 ks2, , , , , , ,( ) =

Mint2 Mint2 ws a1 a2 a E Is ks1 ks2, , , , , , ,( )=⎩⎪⎨⎪⎧

M x( )

Ax B if 0 x a1<≤+

Cx2 Dx E if a1 x a1 a+≤ ≤+ +

Fx G if a1 a x Ll≤<+ +⎩⎪⎨⎪⎧

=

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The suggested method can be applied in the case of a verysmall strip width a (that is, concentrated load), that theoreti-cally could become a line load.

A.5.2 Determination of c2—The coefficient c2 takes intoaccount the loading limited to a width b rather than the totalslab width Lt. It can be determined by applying Betti’stheorem that states, “in a system, applying two sets of forcesPi and Qj that cause two sets of displacements δp and δqrespectively, the work of the forces Pi on the displacementsδqi at the locations i is equal to the work of the forces Qj on

Step 3 Considering the Bernoulli’s equation of the elastic line (neglectingdeformations due to shear)

(A-6)

and integrating twice with respect to x (assuming EIs constant withrespect to x), the deflected shape assumes the form

(A-7)

The 13 constants C1, C2, ..., C13, related to ks1 and ks2, can be deter-mined by means of six compatibility relationships (displacementand rotation at x = 0, x = a1, x = a1 + a, and x = a1 + a + a2) and bymeasurement of at least seven displacements.

Step 4 The absolute displacements d1, d2, ..., d7 have to be measured at thepositions shown in Fig. A.4. Because zero displacement is assumedat the supports, the measures d1, d2, ..., d7 should be transformedinto displacements relative to the slab movement, namely, δ1, δ2, ...,δ7 (where δ1 = δ7 = 0). The displacements δi can be determined as

with i = 1,2, ...., 7

Fig. A.4—Derivation of relative displacements δ.

Step 5 Knowing C1, C2, ..., C13, the form of the measured shape can beapproximated by Eq. (A-7).

Step 6 Using C1, C2, ..., C13, taking the second derivative of Eq. (A-7),plugging it into Eq. (A-6), the constants A, B, C, D, E, F, and G inEq. (A-5) are found.

Step 7 Using A, B, C, D, E, F, and G, the approximate shape of themoment diagram due to wscal is found. Therefore, Mint2, ML2, MR2,and EIs can be derived, where EIs represents the slab constantflexural stiffness.

Step 8 Using Mint2, ML2, MR2, and EIs, the linear system described inEq. (A-4), when ws = wscal, can be solved for ks1 and ks2.

v″ x( ) M x( )EIs

------------–=

v x( )

C1x3 C2x2 C3x C4 if 0 x a1<≤+ + +

C5x4 C6x3 C7x2 C8x C9 if a1 x a1 a+≤ ≤+ + + +

C10x3 C11x2 C12x C13 if a1 a x Ll≤<++ + +⎩⎪⎨⎪⎧

=

δi did7 d1–

a1 a2 a+ +-------------------------xi– di–=


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APPENDIX B—HISTORY OF LOAD TEST, LOAD FACTORS, AND ACCEPTANCE CRITERIA

riSn

the displacements δpj at the locations j.” The application ofthis theorem allows one to determine the relationshipbetween the calculated maximum deflection in System 1(that is, design configuration: Fig. A.1(a)) and the measuredmaximum deflection in System 2 (that is, test configuration:Fig. A.1(c)), as shown in Fig. A.5. In addition, b1, ..., b6

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Fig. A.5—Application of Betti’s theorem (approximatesolution).

represent distances between the sensors in the transversedirection; fI0 represents the displacement at the center inSystem 1; and fII0, …, fII6 represent the displacements at thesensor locations in System 2.

The value of c2 can be obtained as

(A-8)

where ς = b4( fII0 + fII4) + b5( fII4 + fII5) + b6(fII5 + fII6).Thus, c2 is defined only by in-place measured displace-

ments under a load cycle at a load level wscal.

A.6—ConclusionsThe following conclusions can be derived:

• Given w, it is possible to compute ws based on a, b, andthe location of the force of interest; ws is related to w byc1 and c2;

• c1 and c2 can be estimated first by classical analysis;• c1 and c2 can be calibrated during a preliminary load

test at a magnitude wscal under which the slab behavioris linear elastic; and

• For the one-way slab used as an example, the differencebetween preliminary and calibrated load values to attainthe same maximum positive moment at center span wasapproximately 20%, indicating that calibration is animportant step.

c2b1× fII1 fII2+( ) b2 fII2 fII3+( ) b3 fII3 fII0+( ) ς+ + +

2 fI0 b⋅ ⋅-------------------------------------------------------------------------------------------------------------------=

B.1—NotationThe selection of notations reported in this section only

refers to the symbols used in this appendix. Because thisAppendix reports direct quotes from cited references, someof the symbols reported herein may conflict with morecommonly accepted symbols reported elsewhere in thedocument and in this appendix itself.c = distance of external fiber of section from neutral

axis, in. (mm)fc = allowable compressive stress of concrete, psi (N/mm2)fc′ = specified compressive strength of concrete, psi

(N/mm2)h = overall height of member, in. (mm)k = coefficient used to determined value of maximum

deflectionlt = span of member under load test; units (in. or ft)

depend on structural member considered (ACI 318)t = thickness of slab, in. (mm)w = unit weight of concrete, lb/ft3 (kg/m3)n = coefficient reflecting maximum moment in

structural member, dimensionlessm = coefficient reflecting maximum deflection in

can Concrete Institute

-

structural member, dimensionlessD = total dead load; units (lb or kips) depend on

structural member consideredD = maximum deflection in the structure; units (in. or

ft) depend on structural member consideredE = modulus of elasticity of concrete, psi (N/mm2)I = moment of inertia of the section, in.4 (mm4)L = live loads produced by use and occupancy of the

building not including construction, environmentalloads, and superimposed dead loads; units (lb orkips) depend on structural member considered

L = span of structural member; units (in. or ft) dependon structural member considered

Mf = factored load generating bending momentaccording to the Canadian Standard Association

N = number of total eventsPf = factored load generating normal force according to

the Canadian Standard AssociationTL = test load per ACI 318 before 1971; units (in. or ft)

depend on structural member consideredTL05 = test load per ACI 318-71 through 318-05; units (lb

or kip) depend on structural member consideredVf = factored load generating shear force according to

the Canadian Standard AssociationW = applied load; units (lb or kip) depend on structural

member consideredΔ = maximum deflection in structure; units (in. or ft)

depend on structural member consideredΔmax = measured maximum deflection, in. (mm)

B.2—Historical load test practice in the United States and according to ACI

B.2.1 Early history in the United States from 1890 to1920—The practice of load testing concrete structures in theU.S. began late in the 1890s as a method of proof testingnewly constructed concrete systems and structures. Devel-opment of reinforced concrete structures in this country, aswell as abroad, was fostered by the development ofnumerous proprietary reinforcement systems. Examplesinclude the Hennebique system developed in France in the1870s and patented in 1892 by Francois Hennebique(Hennebique 1909); the Ransome system patented by ErnestL. Ransome in 1884 in the United States; the Kahn systemthat was developed by Julius Kahn and used extensively by

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his brother, Albert Kahn, between 1900 and 1920; and theTurner system of reinforced concrete construction, developedin the early 1900s by C. A. P. Turner. Proof load testing ofthose systems and many others is widely reported in theliterature between 1890 and 1920.

The Ward House, built in Port Chester, N.Y., from 1873 to1876 and constructed by William E. Ward, is generallyrecognized as the first reinforced concrete structure in theUnited States. Ward employed load testing during theconstruction of this residence as a means of proving theviability of this new and unique method of construction, asreported by Kramer and Raafat (1961):

...Ward undertook numerous field tests of his new systemfrom which acceptable results for deflection and strengthwere obtained. Before constructing any of the floors, hesubjected a sample beam to a weight far beyond its normalload carrying capacity. After the parlor floor had been laidfor 1 year, he piled a weight of 26 tons between the twocentral beams, leaving it there over the winter; at the end ofthe testing period, the amount of deflection was only onehundredth of an inch. Ward was an eminently practical manwho believed in putting his theories to the most rigid tests.He also carried out experiments on flat slabs of concretesupported on all four sides.

Another early example of proof load testing of a newconcrete structure was reported by Birkmire in 1894:

A section of a flat floor in the California Academy ofScience, 15 x 22 ft, was tested in 1890 with a uniform loadof 415 lb per square foot, and the load left on for 1 month.The deflection at the center of the 22 ft space was only 1/8 in.

An early example of the incorporation of load testing intothe design of reinforced concrete buildings is Frank LloydWright’s 1906 design of the Unity Temple in Oak Park, Ill.(Wright 1906) Wright prepared design documents thatcontained the following performance specification for thestructural design of the concrete structure of this remarkablehistoric building:

Throughout floors shall be constructed to carry safely auniformly distributed superimposed live load of 100 poundsper square foot with a maximum deflection of 1/800 of thespan.

This was immediately followed with a provision requiringa full-scale load test to ensure that all work met this perfor-mance specification.

Floor shall be tested in approved manner, at expense of thiscontractor at any point after cement has set 15 days. They shallbe subjected to twice the loading specified for live load withinthe limits of the deflection specified and after removal ofloading shall resume position previous to test. Any work notpassing test shall be replaced and brought to test requirements.

This early specification for proof load testing of a newlyconstructed concrete structure contained several of the basic

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elements of load testing that are found in our modernbuilding codes:• Specification of a minimum age of the structure before

testing; in this case, 15 days;• Specification of a minimum test load; in this case, two

times the live load;• Specification of a maximum acceptable deflection; in

this case, the span length divided by 800 (lt /800); and• Specification of a required deflection recovery; in this

case, apparently 100% as the maximum deflectionduring the load test was to be recovered upon removalof the superimposed test load.

The earliest building code reference for load testing ofreinforced concrete structures that this committee has foundis the 1903 New York City Building Regulations (Urquhartand O’Rouke 1926) that contained the following:

The Contractor must be prepared to make load tests on anyportion of a concrete-steel-construction, within a reasonabletime after erection, as often as may be required by the Super-intendent of Buildings. The tests must show that theconstruction will sustain a load of three times that for whichit is designed without any sign of failure.

Another early building code reference to load testing ofconcrete structures can be found in the Chicago BuildingOrdinance adopted in December of 1910 that states thefollowing:

Tests shall be made by the owner upon the demand of theCommissioner of Buildings on all forms of constructioninvolving spans of over 8 ft. Such tests shall be made to theapproval of the Commissioner of Buildings and must showthat the construction will sustain a load equal to twice thesum of the live and dead loads, for which it was designed,without any indication of failure. Each test load shall remainin place at least 24 hours.

Each test load shall cover two or more panels and shallremain in place at least 24 hours. The deflection under thefull test load at the expiration of 24 hours shall not exceed1/800th of the span. These tests shall be considered as testsof workmanship only.

The first code requirement for load testing of concretestructures in this country by a national organization is thatcontained in the National Association of Cement Users’(NACU) 1908 document entitled “Report of the Committeeon Laws and Ordinances”:

The contractor must be prepared to make load tests on anyportion of a reinforced concrete constructed building withina reasonable time after erection as often as may be requiredby the commissioner of buildings. The tests must show thatthe construction will sustain a load with a factor of safety forfloors and structural members as required by Section 126 ofthis code.

The NACU was the forerunner to the American ConcreteInstitute. The NACU’s 1910 “Standard Building Regulations

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for the Use of Reinforced Concrete” did not include anyguidance on load testing.

In 1912, W. S. Slater published what may have been thefirst state-of-the-art report on load testing of reinforcedconcrete buildings in the United States. That documentcontains the following statements regarding the intent ofload tests:

Load tests have been required by city building departmentsand as a condition of acceptance of reinforced concretebuildings and have been used by construction companies andengineers to demonstrate the adequacy of various designs.Such load tests are never continued to destruction, theapplied load being generally twice the design live load, andemphasis is placed upon measurement of deflections andrecovery. No measurement of stresses is made in such testsand under these conditions the safe load cannot be fixedupon as a definite ratio of the ultimate load.

This document clearly shows the importance of the deflec-tion response in evaluating a load test.

At about the same time, Emile G. Perrot summarized theprevailing mood regarding the intent of load tests amongcontemporaries (Perrot 1911).

These load tests are made, not with a view of obtainingscientific data, but more particularly of satisfying both thearchitects and the owners that the work of the contractor hadbeen properly performed, and that the building would sustainthe loads for which it was designed.

Perrot also provided insight in that same documentrelating to the possible origin of the use of a test load of 2.0times the superimposed live load, as follows:

The practice now is to require a floor to be tested to doublethe live load without sign of fracture and that after the loadis removed the floor must recover its normal position. It isthe writer’s belief that many specifications require a too rigidtest by imposing the requirement of loading the floor to threeor more times the live load. A little consideration will showthe fallacy of this requirement, because it is not desirable totest an actual floor of a building so as to stress the reinforce-ment to a point equal to or greater than its elastic limit, as thiswould permanently weaken the section of the floor so test.Take for example a floor designed for a live load of 200 lbper sq ft; assume the test load to be three times the live load;also assume the dead weight of the construction to be 75 persq ft. Then as usually computed with a factor of safety of 4,the breaking load of the floor would be 1100 lb per sq ft. Iffrom this is deducted the dead weight of 75 lb per sq ft, theload to break the floor is 1025 lb per sq ft. If a test load ofthree times 200 lb, or 600 lb per sq ft is applied, there islikelihood of the reinforcement being stretched beyond itsyield point, or elastic limit, because the average elastic limitof medium steel is one-half its ultimate strength. Hence a testload that exceeds more than one-half of 1025 lb, or about500 lb, should not be applied. This, it will be noticed, isabout 2-1/2 times the live load. The requirement of theBureau of Building Inspection of Philadelphia for a test loadis two times the live load.

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T. L. Condron presented an important paper in 1917 at the9th Annual Conference of the NACU entitled, “Principles ofDesign and Results of Test on Girderless Floor Constructionof Reinforced Concrete” (Condron 1917). The followingdiscussion relevant to the issues of appropriate test loads andthe corresponding maximum allowable deflection in a loadtest is contained in the written paper published in theproceedings of that conference:

A test load equal to twice the live load (where the live loadis greater than the dead load) seems to me to be the maximumtest load that should be called for. With regard to the properamount of deflection, which should be considered satisfactory,under test load, this can only be arrived at by careful study ofthe many tests that have been made on various types ofconstruction. The permissible deflection, under test load,should be less than the deflection that produces visiblecracks in the finished concrete surface of the floor or ceiling.Reinforced concrete structures should not be subjected toloadings that will produce visible cracks, and certainlystructures should be so designed that working loads will notproduce cracks.

….a limit of 1/800th of the diagonal span for a single paneltest of double the live load would be entirely reasonable, butis apparently too severe a limitation where the test load ismade to cover two panels and is equal to twice the live, plusthe dead load. For such a test, the permissible deflectionshould be at least 1/600th of the diagonal span.

The “Second Report of the Joint Committee on Concreteand Reinforced Concrete” was published in the 1913proceedings of the American Society of Civil Engineers, andcontained the following guidance on load testing:

Load tests on portions of the finished structure shall be madewhere there is reasonable suspicion that the work has notbeen properly performed, or that, through influences of somekind, the strength has been impaired. Loading shall becarried to such a point that one and three-quarters times thecalculated working stresses in critical parts are reached, andsuch loads shall cause no injurious permanent deformations.Load tests shall not be made until after 60 days of hardening.

The load testing requirements in this document wereaimed at defective or questionable new structures, ratherthan proof testing, which proved to be somewhat of ananomaly at that time.

The 1916 proceedings of the 12th Annual Conference ofACI contained the following guidelines for proof loadtesting (Committee on Reinforced Concrete and BuildingsLaws 1916):

The Superintendent of Buildings may require a load test on afloor within reasonable time of the erection. The test shall bemade under the supervision of the Superintendent of Buildingsand shall show that the construction will sustain safely anapplied load of twice the total live load, but in no case less thanone and one-half times the total live and dead load.

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Table B.1—Summary of ACI code requirements for load testing practice

Year Minimum age

Total test load

Duration of loadMaximumdeflection

Deflectionrecovery NotesD L

1916 — 1.00 2.00 — — — —

1917 60 days 1.00 2.00 — — 80% at 3 days —

1920 60 days 1.50 1.50 — l/800 80% at 7 days —

1924 30 days 1.50 1.50 24 hours None 75% at 24 hours —

1928 60 days 1.50 1.50 24 hours None 75% at 24 hours —

1936 None 1.50 1.50 24 hours lt2/12,000h 75% at 24 hours —

1941 None 1.50 1.50 24 hours lt2/12,000h 75% at 24 hours —

1947 None 1.50 2.00 24 hours lt2/12,000h 60% at 24 hours

Structure fails if deflection exceeds three times lt

2/12,000h

1951 None 1.50 2.00 24 hours lt2/12,000h 60% at 24 hours

Structure fails if deflection exceeds three times lt

2/12,000h

1956 56 days 1.00 2.00 24 hours lt2/12,000h 75% at 24 hours Multiple limits on maximum

acceptable deflections added

1963 56 days 1.30 1.70 24 hours lt2/20,000h 75% at 24 hours —

1971 through 2005 56 days 1.19 1.45 24 hours lt2/20,000h 75% at 24 hours —

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Provisions for load testing progressed a little further in the1917 proceedings of the 13th Annual Conference of ACI(Committee on Reinforced Concrete and Buildings Laws1917). This report included the first appearance of deflectionrecovery as an acceptance criterion in an ACI document andof a requirement for the minimum age of a structure at timeof test:

The Building Department may require the Owner to makeload tests on portions of the finished structure where there isa reasonable suspicion that the work has not been properlyperformed, or that, through influences of the same kind, thestrength has been impaired, or where there is any doubt as tothe sufficiency of the design. The test shall show that, with aload of twice the design live load, the permanent deflectionseveral days after load is removed to be not more than 20%of the total deflection under the test load. Load tests shall notbe made before the concrete has been in place 60 days.

B.2.2 1920 ACI regulations for reinforced concrete—ACIissued “Standard Specifications No. 23—Standard BuildingRegulations for the Use of Reinforced Concrete” in 1920(American Concrete Institute 1920). That documentcontained the following basic provisions for proof loadtesting of structures:• Establishment of a specific applied superimposed test load

of two times the live load; that is, TL = 1.0D + 2.0L;• Establishment of a maximum acceptable total deflection

for flexural members of lt /800;• Use of deflection recovery as an acceptance criterion;

that is, recovery to be equal to or more than 80% ofmaximum deflection at 7 days after load removal;

• Specification of 56 days as the minimum age of structurebefore testing would be allowed;

• Allowance for retesting a structure that failed a loadtest; and

• Provision for reducing the allowable live load when astructure did not pass a load test.

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This set of criteria formed the foundation for the loadtesting provisions contained in all future ACI codes throughthe ACI 318-05. Various changes were made to the ACI1920 criteria with nearly each subsequent issuance of ACIregulations or requirements, as summarized in Table B.1 andas discussed as follows.

B.2.3 1928 ACI tentative regulations—In 1928, ACIissued “Tentative Building Regulations for ReinforcedConcrete” (ACI Committee E-1 1928). The superimposedtest load was modified to include 1.5 times the live load plusone half of the dead load added to the self-weight; that is, TL= 1.5D + 1.5L. No maximum deflection criterion wasprescribed. The structure was considered to have failed the testif, within 24 hours after the removal of the load, the slabs orbeams did not show a recovery of at least 75% of the maximumdeflection recorded after the 24-hour holding period.

B.2.4 1936 and 1941 ACI building regulations—In 1936,ACI issued the “Building Regulations for ReinforcedConcrete (ACI 501-36T)” (“T” indicates this was a tentativestandard) (American Concrete Institute 1936). The TLM wasnot changed; however, an important change was introduced.The maximum acceptable deflection Δ was defined as thefollowing

Δ = 0.001L2/12t (B-1)

where L = the span (lt in this report and ACI 318-05), and t= total depth of the slab or beam (h in the notation of thisreport and ACI 318-05), expressed in the same units as spanand deflection.

This general form of the deflection acceptance criterionhas been in the ACI Building Code ever since. Because theorigin of this important and lasting criterion in ACI 318 hasbecome lost to most current practitioners, it is discussed insome detail herein, and the derivation of Eq. (B-1) is shown.

In 1909, C.A.P. Turner (Turner 1912) discussed the funda-mental principle of engineering mechanics behind this


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equation, indicating that according to elastic theory, thedeflection due to the test load would vary roughly as thesquare of the span divided by the depth for a fixed maximumstress, assuming a fixed ratio of the thickness of a slab to itsspan. Following is his discussion on this topic; but first, thesymbols are defined:c = distance of extreme section fiber from neutral

axis;fc = allowable compressive stress;h = height of section;E = modulus of elasticity of concrete;I = moment of inertia of section;L = span of structural member;W = applied load; andΔ = maximum deflection in structure.

From the theory of elasticity for flexural members

W =

where c = h/2 for an uncracked section, and n = 4, 8, 8, or 12for the four different cases, namely: simple and restrainedbeams loaded with W concentrated at center and Wuniformly distributed.

The requirement of stiffness (that is, a given maximumdeflection) limits the load by a different formula

W = m

where m = 48, 76.8 (that is, 384/5), 192, or 384 for the samefour cases.

By equating these values of W the relation between Δ andfc is obtained

Δ =

This shows that the maximum deflection for the same unitstress varies as L2/c for beams of the same material, whilecoefficients n and m result in additional variation. Of course,such variations make it impossible to limit the permissibledeflection to a fixed percent of the span.

ACI 501-36T (American Concrete Institute 1936)included the following regarding the allowable compressivestress and the modulus of elasticity of concrete:

Allowable compressive stress fc = 0.4fc′ (Section 305)Modulus of elasticity E = 1000fc′ (Section 601)

Thus, the ratio of fc/E = 1/2500, and for the case where c =h/2 (for an uncracked section), the equation for maximum Δbecomes

(B-2)

n fc I⋅ ⋅L c⋅

-----------------

E I Δ⋅ ⋅

L3------------------

n L2 fc⋅ ⋅m c E⋅ ⋅---------------------

Δn lt

2 fc⋅ ⋅m c E⋅ ⋅-------------------

n lt2⋅

m 1250 h⋅ ⋅----------------------------= =

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Then, for concrete with fc′ of 2000 psi (13.8 MPa)—atypical strength in the early 1900s—the fc = 0.4fc′ = 800 psi(5.52 MPa), and the E = 1000fc′ = 2,000,000 psi (13.8 GPa).The maximum deflections as a function of beam type andload distribution are listed in Table B.2.

These values of Δmax for each condition of end restraint areconstant with variations in concrete strength because theratio fc /E is constant, at least as defined in ACI 501-36T.

This derivation of the equation for maximum deflection of auniformly loaded simply supported beam, Δmax = lt

2/12,000h,is also confirmed in the 1950 publication in Israel, “Researchon Loading Tests of Reinforced Concrete Structures” (Arnanet al. 1950).

It is evident that this original equation for maximumallowable deflection is based on simple span conditions,uncracked concrete sections, and concrete strengths andelastic moduli significantly below those used today.

B.2.5 ACI 318-47 and 318-51—In ACI 318-47, thefollowing changes were made to the guidelines for loadtesting:• The superimposed test load was increased to half the

dead load plus twice the live load added to the self-weight; that is, TL = 1.5D + 2.0L;

• The maximum allowable deflection was maintained atlt

2/12,000h despite the increase in test load;• The deflection recovery requirement was reduced from

75% of maximum deflection to 60%; and• The provision was added that the structure fails the load

test and no retesting is allowed if maximum deflectionis greater than 3 times lt

2/12,000h.No changes were made to these load test provisions in ACI

318-51.B.2.6 ACI 318-56—Substantial changes were made to load

testing criteria in ACI 318-56. The additional dead loadrequirement was dropped, and the test load was returned totwo times the live load only. The maximum deflection criterionwas significantly expanded, as shown in the direct quotes fromACI 318-56, Section 203 (where symbols were defined as t= height of the section, D = maximum deflection in thestructural member, and L = span of the structural member):

(a) If the structure shows evident failure, the changes or modi-fications needed to make the structure adequate for the ratedcapacity shall be made; or a lower rating may be established;

(b) Floor and roof construction shall be considered toconform to the load test requirements if there is no evidenceof failure and the maximum deflection does not exceed

D = L2/12,000t…………………(1)

Table B.2—Maximum deflectionType of beam Type of load distribution Δmax

Simple span beamUniform load lt

2/12,000h

Point load at midspan lt2/15,000h

Fixed end beamUniform load lt

2/40,000h

Point load at midspan lt2/30,000h

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In which all terms are in the same units. Constructions withgreater deflections shall meet the requirements of subsections(c), (d), and (e);

(c) The maximum deflection of a floor or roof constructionshall not exceed the limit in Table 203(c) considered by theBuilding Official to be appropriate for the construction;

(d) The maximum deflection shall not exceed L/180 for afloor construction intended to support or be attached topartitions or other construction likely to be damaged by largedeflections of the floor; and

Deflection recovery and provisions for retesting wereincluded as follows:

(e) Within 24 hours after the removal of the test load therecovery of deflection caused by the application of the testload shall be at least 75% of the maximum deflection if thisexceeds L2/12,000t. However, constructions failing to show75% recovery of the deflection may be retested. The secondtest loading shall not be made until at least 72 hours after theremoval of the test load for the first test. The maximumdeflection in the retest shall conform to the requirements ofSections 203(c) and (d) and the recovery of deflection shallbe at least 75%.

B.2.7 ACI 318-63—In ACI 318-63, ultimate strengthdesign was introduced as an alternate to working stressdesign. The test load in a load test was redefined as super-imposed 30% of the dead load plus 1.7 times the live loadadded to the self-weight; that is, TL = 1.3D + 1.7L. Theextent to which this test load would vary from the require-ment of ACI 318-56 depended on the relative magnitudes of

Table 203(c)—Maximum allowable deflectionConstruction Deflection

1. Cantilevered beams and slabs L2/1800t

2. Simple beams and slabs L2/1800t

3. Beams continuous at one support and slabs continuous at one support for the direction of the principal movement

L2/9000t

4. Flat slabs (L = the longer span) L2/10,000t

5. Beams and slabs continuous at the supports for the direction of the principal reinforcement L2/10,000t

Table B.3—k coefficient

Type of beam

Type of load

Values of coefficient k in deflection equation for various values of concrete compressive strength fc′ , psi (MPa)

2000 (13.8)

2500(17.2)

3000(20.7)

3750(25.9)

4000(27.6)

5000(34.5)

Simple span

Uniform load 13,800 12,300 11,200 10,000 9700 8700

Point load at

midspan17,200 15,400 14,000 12,500 12,200 10,900

Fixed ends

Uniform load 45,800 40,800 37,400 33,500 32,400 29,000

Point load at

midspan34,400 30,700 28,000 25,100 24,300 21,700

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dead and live loads and could be either higher or lower than theACI 318-56 test load. The 24-hour holding period for the testload was reaffirmed. The acceptance criteria, however, weremade more restrictive. The maximum allowable deflection atthe end of the 24-hour holding period was reduced signifi-cantly to Δmax = lt

2/20,000h. If that deflection limit was to beexceeded, then recovery of deflection within 24 hours afterremoval of the test load was to be at least 75% of themaximum deflection to pass the test. The maximum allowabledeflections provided in Table 203(c) of ACI 318-56 weredropped from the 1963 code.

The rationale behind the change of the maximum allowabledeflection from lt

2/12,000h to lt2/20,000h is unknown to

Committee 437. In an attempt to understand why this changewas made, one should note that the values for allowablecompressive stress in the extreme fiber of a flexural memberin bending fc and the relationship for the modulus of elas-ticity E were changed in ACI 318-63 as follows:

Allowable compressive stress fc = 0.45fc′ (Section 1002)Modulus of elasticity E = w1.533√fc′ (Section 1102)

where w = unit weight of concrete.Table B.3 provides a summary of the values in the coefficient

k used for computing the maximum deflection according tothe equation Δmax = lt

2 /kh, where k = mE/2nfc′ for variousvalues of fc′ and various conditions of loading and end fixity,based on these 318-63 parameters and using Eq. (B-2)developed in Section B.2.4 of this report.

Table B.3 shows that the k values and, therefore, the corre-sponding beam deflections that result from variations in theend fixity and load type, vary by more than 300%. This is aclear illustration of the inadequacies of using a single valuesuch as 12,000 or 20,000 for computing the maximumacceptable deflection during a load test for all conditions ofend restraint and different concrete strengths.

B.2.8 ACI 437-67—ACI Committee 437 published thefirst version of “Strength Evaluation of Existing ConcreteBuildings” in 1967 (ACI Committee 437 1967). That documentprovided extensive guidance for load testing of existingconcrete buildings. The following specific criteria wereincluded:• Test load:

– Where the strength of a whole structure is underinvestigation, test load TL = 1.25D + 1.50L, or TL =1.50D, whichever is greater; and

– Where the strength of only a portion of a structure isunder investigation, test load TL = 1.30D + 1.70L, orTL = 1.60D, whichever is greater.

• Duration of test load = 24 hours;• Maximum allowable deflection = lt

2/20,000h; and• Deflection recovery = 75% at 24 hours after load

removal.When Committee 437 revised its report in 1982 (ACI

Committee 437 1982), the test load was no longer separatelydefined for tests on portions of a structure versus tests on awhole structure. Instead, the single definition for the TLM asgiven in ACI 318-71 and later editions was recommended.


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Of particular interest, it was indicated in this report that ifthe maximum deflection of a reinforced concrete flexuralmember is smaller than lt

2/20,000h, elastic behavior may beassumed, and the recovery of deflection requirement statedabove may be waived. This is the first and only reference toa correlation between the equation for maximum allowabledeflection under test load and the assumption of linear elastic(uncracked) behavior. No technical basis is given for statingthat there is a correlation between this maximum deflectionand the assumption of elastic or inelastic behavior of areinforced concrete structure or structural component.

Finally, the following provision is included in the ACI437R-67 that dealt with serviceability (where L = live load):

If serviceability is also a criterion in the evaluation of thestructure, the deflection at the superimposed load level of1.0L, in addition to the simulated dead load, for any part ofthe structure should not exceed that stipulated by theauthority, and the significance of any cracks should be dulyconsidered.

This is believed by Committee 437 to be the first referencein any historical ACI document to consider serviceability ina load test of a concrete structure. This provision was main-tained in subsequent editions of ACI 437R.

B.2.9 ACI 318-71—In ACI 318-71, the test load was againredefined, this time as equivalent to 0.85(1.4D + 1.7L); thatis, TL05 = 1.19D + 1.45L. The acceptance criteria for a loadtest remained essentially unchanged from ACI 318-63,despite this reduction in test load intensity. The Commentaryto ACI 318-71 acknowledged that the new test load representeda reduction of approximately 8 to 15% from the previouscode, depending on the ratio of live load to dead load. Thecommentary (ACI 318R-71) noted the following:

The new procedure has the advantage, however, that the testload is a constant percentage of the theoretical design strength.This reduction in testing load avoids possible problems intesting of prestressed members where load values stated inACI 318-63 might induce inelastic behavior even in amember, which proves to have adequate strength capacity.

The maximum deflection criterion, Δ = lt2/20,000h, was

not modified despite the reduction in TLM.No changes have been made to the provisions in Chapter 20

of ACI 318 in any subsequent edition of that document since1971 in the areas of magnitude of test load or the maximumdeflection and deflection recovery acceptance criteria.Table B.1 provides a summary of ACI code requirements asthey relate to load testing practice.

B.2.10 Cyclic load testing of concrete structures—Mettem-eyer (1999) provided a summary of the cyclic load test (CLT)method, (Section 6.2). It included a description of the generalconcepts, objectives, planning, evaluation of the structure,selection of members to be evaluated, methods of load appli-cation, TLM, prediction of structural responses, equipmentthat may be used, analysis during testing, interpretation ofresults, and descriptions of commercial applications.

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This document (Mettemeyer 1999) also presented the useof the CLT procedure that was carried out in five casestudies. All five of the case studies involved beam specimensthat were strengthened with externally applied carbon fiber-reinforced polymer (CFRP), and each specimen was loadedso that it would fail in shear. The five case studies aresummarized as follows:

Case study No. 1: Prestressed double T-beam—Thisstudy was conducted in a controlled laboratory environment.The dapped ends of the double T-beam were strengthenedwith CFRP. This dapped end was the area under investigation;therefore, the double T-beam was loaded in shear in such away that the reactions were greater than 85% of the factoreddesign loads. The CLT performance measures (explained indetail in Section 5.2) of repeatability, permanency, andmaximum deviation from linearity were 98, 4 (maximum),and 12%, respectively. These values were indicative ofacceptable behavior as discussed in Section 6.2. For the 24-hourload test method, when the performance measures ofpermanency and maximum deviation from linearity wereapplied, the values of 3 and 22% were obtained. Repeatabilitycould not be calculated with the 24-hour load test procedurebecause this performance measure requires repeated cycling.Loading to failure after completion of the tests indicated thatthe maximum test load was approximately 50% of theultimate capacity of the specimen.

The following studies (Cases 2 to 5) were conducted in thefield. In the entire study, 20 reinforced concrete ceiling joistswere tested using the CLT technique, and were also taken tofailure to determine their true capacities. Sixteen of themembers were strengthened with CFRP, with the remainingfour serving as control specimens. The net deflectionachieved during the 24-hour load test was essentially thesame as that achieved during the CLT for all cases.

Case study No. 2: Short span ceiling joist (shearcapacity, strengthened with CFRP)—This ceiling joistwas strengthened with CFRP and was tested in shear-to-loadlevels that were calculated to exceed 85% of the factoreddesign loads. The CLT performance measures of repeat-ability, permanency, and maximum deviation from linearitywere 104, 5 (maximum), and 21%, respectively. Loading tofailure after completion of the tests indicated that themaximum test load was approximately 45% of the ultimatecapacity of the specimen. From the load versus deflectionbehavior, it was determined that the level of load to achievea 25% deviation from linearity (threshold value explained inSection 6.2) was approximately 52% of ultimate capacity.

Case study No. 3: Short-span ceiling joist—Thisspecimen was similar to that for case study No. 2 with theexception that two plies of CFRP reinforcement were usedas opposed to only one ply for the joist in case study No. 2.The CLT performance measures of repeatability, permanency,and maximum deviation from linearity were 102, 2(maximum), and 21%, respectively. Loading to failure aftercompletion of the tests indicated that the maximum testload was again approximately 45% of the ultimate capacityof the specimen. From the load-versus-deflection behavior,

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it was determined that the level of load to achieve a 25%deviation from linearity was again approximately 52% ofultimate capacity.

Case study No. 4: Long-span ceiling joist—This spec-imen was strengthened with one ply of CFRP without an endanchor. The CLT performance measures of repeatability,permanency, and maximum deviation from linearity were100, 3 (maximum), and 20%, respectively. Loading tofailure after completion of the tests indicated that themaximum test load was approximately 17% of the ultimatecapacity of the specimen. From the load-versus-deflectionbehavior, it was determined that the level of load to achievea 25% deviation from linearity was approximately 27% ofultimate capacity.

Case study No. 5: Long-span ceiling joist (shearcapacity)—This specimen was similar to the joist in casestudy No. 4 with the exception that an end anchor was usedwith the CFRP strengthening. The CLT performancemeasures of repeatability, permanency, and maximumdeviation from linearity were 103, 5 (maximum), and 24%,respectively. Some change in deflection was noticed duringthe 24-hour load test, and this was attributed to temperature.Loading to failure after completion of the tests indicated thatthe maximum test load was approximately 35% of theultimate capacity of the specimen. From the load-versus-deflection behavior, it was determined that the level of loadto achieve a 25% deviation from linearity was approximately41% of ultimate capacity.

B.2.11 CIAS Report 2000 and ACI 437R-03—In 2000, theConcrete Innovations Appraisal Service (CIAS), a subsid-iary of the Concrete Research and Education Foundation,issued its appraisal report, “Guidelines for Rapid LoadTesting of Concrete Structural Members,” (CIAS 2000). Thereport discussed the CLT method as an alternative methodfor evaluating structures by load testing. The report wasreviewed by a panel consisting of ACI members, some ofwhom were members of ACI Committee 437. The panel’sappraisal of the information submitted stated the following:

The panel’s opinion is that the proposed Rapid Load Testprotocol has great potential value to the construction industry.The method has the potential for making load testing of newstructures, deteriorated structures, and repaired structuresmore practical and more meaningful than the present 24-hourstatic load test presented in the American Concrete Institute“Building Code Requirements for Structural Concrete (ACI318-99),” Chapter 20. The controlled cyclic loading andcontinuous monitoring and evaluation of measured responsesare seen by the panel as having real value... the panel feels thatthe method’s potential advantages make it worthy of furtherdevelopment and submission to ACI Committee 437—Strength Evaluation of Existing Structures, and ACICommittee 318—Building Code. The Rapid Load Testmethod could supplement or form the basis for a revision tothe current Chapter 20 strength evaluation provisions.

The information contained in the CIAS report was subse-quently reviewed and discussed in Committee 437. Thecyclic load test method was reported in Appendix A of ACI

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437R-03, which provided details on the procedure and asuggested protocol.

B.3—Other historical load test practicesThe following is a discussion of load test practices in

various parts of the world dating back to 1903. This discus-sion is not presented as an all-encompassing summary; itmerely represents information the Committee has been ableto uncover to date. The major components of this discussionare summarized in Table B.4.

B.3.1 Proceedings of 5th Annual Convention, NationalAssociation of Cement Users (NACU 1908)—This documentincludes one of the earliest summaries of existing buildingregulations from around the world relating to load testing ofconcrete structures. Pertinent portions of a tabulated summaryof these regulations are quoted in the following sections.

B.3.1.1 Swiss Society of Engineers and Architects: 1903recommendations—• “Test load to be at least 50% greater than working loads

allowed in calculations.”• “Test loads not to be put on until 45 days have been

allowed for setting.”• “If possible deflections of different stages of loading to

be noted.”B.3.1.2 Prussian government regulations: 1904—

• “If loading tests are necessary, they are to be carried outunder instruction of representative of building authority.”

• “When a strip is cut from a floor or decking is tested,the load shall be uniformly distributed and shall notexceed the weight of the strip and twice the workingload. If a strip is tested in-situ the above loading shallbe increased by one-half.”

B.3.1.3 French government rules: 1907—• “Conditions of test and time that shall elapse before struc-

tures are brought into use must be inserted in contract,and also, the maximum deflection as far as practicable.”

• “The time to elapse before use of structures must be90 days for structures of primary importance, 45 daysfor ordinary constructions, and 30 days for floors.”

• “Measurements to be taken during test, which are likelyto be of scientific interest to engineers.”

• “Test loads on floors shall be the dead and superim-posed loads acting over the whole area of the floor, or atleast upon a complete panel.”

• “The loads to be left on for at least 24 hours, anddeflection to cease after 15 hours.”

B.3.1.4 British Reinforced Concrete Committee: 1907recommendations—• “Loading tests not to be made till 2 months after

completion.”• “Test load not to exceed 1-1/2 times superimposed

loading.”• “Consideration to be given to adjoining parts of a

structure in case of partial loading.”• “No test load to be applied, which would cause metal to

be stressed more than 2/3 of its elastic limit.”B.3.1.4 Austrian Ministry of Interior Rules: 1908—

• “Breaking tests of whole or part to be made on request.


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Table B.4—Sampling of load test requirements other than those from ACI

Year and documentMinimum

age

Total test load Duration of load

Maximumdeflection

Deflectionrecovery NotesD L

1903: New York City BuildingRegulations — 1.00 3.00 — — — —

1903: Swiss Society of Engineers and Architects (NACU 1908) 45 days 1.50 1.50 — — — —

1904: Prussian GovernmentRegulations (NACU 1908) —

1.00 2.00— — —

Test load for an isolated member

1.00 3.00 Test load for a nonisolated member

1907: French Government Rules (NACU 1908)

90 days

— — 24 hours No deflections after 15 hours —

Structures of primary importance

65 days Ordinary construction

30 days Floors

1907: Great Britain (NACU 1908) 2 months 1.00 1.50 — — —No test load to be applied that would cause metal to be stressed more than 2/3 of its elastic limit

1908:Austrian Ministry of the Interior

Rules (NACU 1908)6 weeks 1.00 1.50 — — No permanent

deflectionsAcceptance criteria: no cracks or permanent deflections

1908: Borough of Manhattan, N.Y. — 1.00 3.00 24 hours — — Acceptance criteria: no sign of failure

1908: Borough of Brooklyn, N.Y. — 1.00 2.00 — L/700 — —

1908: Buffalo, N.Y. — 1.00 3.00 — — — Acceptance criteria: no sign of failure

1908: Chicago, Denver,San Francisco — 1.00 2.00 — L/700 — —

1908: Toledo, Ohio — 1.00 3.00 — — — Acceptance criteria: no sign of failure

1908:Baltimore, Md. — 1.00 2.00 — — — Acceptance criteria: no sign of failure

1910: Chicago Building Ordinance — 1.00 2.00 24 hours — — —

1926: Russia — — — — L/750 67% No further information available on testprocedures

1934: Building Research Board, Code of Practice for RC 56 days 1.00 1.50 24 hours — 75% Repeat load test if deflection recovery is

not met

1957: CP 114, The Structural Use of RC in Buildings, British Standard

Code of Practice56 days 1.00 1.25 24 hours Not undue 75% —

1959: CP 115, The Structural Use of PC in Buildings, British Standard

Code of Practice56 days 1.00 1.25 24 hours Not undue 85% For prestressed concrete

1963: Australian AS CA-2 56 days 1.00 2.00 24 hours L2/cd 75% Coefficient c has values from 1800 to 10,000, depending on type of construction

1964: European Concrete Committee (a) 1.00 1.00 to 1.10 (b) (b) (b)

(a) Concrete to have reached strengthspecified by engineer(b) To be decided by engineer before test

1964: Institution of StructuralEngineers — 1.10 1.25 8 hours L /360*

L /250† 75%Crack width acceptance criteria also:*for live load only†for dead plus live

1975: RILEM TBS-2,General Recommendation

for Loading Tests56 days 1.20 1.40 16 hours —

75%*

87.5%†

80%‡

*For new structures†For structures already used and exposed to load‡Precast concrete structures

1977: Czechoslovakia StateStandard—CSN 73 2030 3 months 1.00 1.05 to

1.25 24 hours Code values× 1.1 to 1.2 75% Crack width acceptance criteria also

1994: CSA A23.3 (CSA 1994) 28 days1.125 1.35

— — 60%For whole structures under investigation

1.25 1.50 For portions of structures under investigation

1995: Building ResearchEstablishment (BRE 1995) — 1.25 1.25 24 hours Code values 90% —

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ericHS ion

No test before expiration of six weeks after completionof ramming.”

• “Loading to be such that effect is same as dead loadplus 1-1/2 specified superimposed load. No cracks orpermanent deflections.”

• “For breaking tests load to be gradually increased.”• “Breaking load not to be less than 3-1/2 times the total

dead and superimposed loads, less the weight of themember.”

an Concrete Institute under license with ACI License

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This 1910 NACU document also contained a tabularized

summary of requirements for load testing in the time frame

of 1908 in the United States. Pertinent excerpts from that

summary appear in Table B.4.B.3.2 Research on loading tests of reinforced concrete

structures: report of work carried out at standards Institu-

tion of Israel (Arnan et al.) in 1950—This report outlines the

findings of interesting research performed at this organization


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before 1950 in the area of load testing. The introduction ofthis report includes the following noteworthy text:

The loading test is generally regarded as an indication of thesafety of the structure. Whereas on one hand it has beenknown for years that this test is entirely unreliable, on theother hand, the scientific foundation of this test has beenquestioned in recent years. The board for Scientific andIndustrial Research had therefore authorized a researchproject, the object of which was to clarify the physicalfoundations of the loading tests.

The document also contains the following statements:

The significance of the load test has often been questioned.At the laboratories of the Institution, about 25 such tests havebeen performed since 1945, and it is notable that, although inall cases the strength of the structure was under suspicion; inno case failure to comply with the load test was found. Thispeculiarity of the load test to favour the builder is wellknown to contractors.

The history of the load test and the theory underlying it aredifficult to trace…all specifications in the various countrieswhere a load test is prescribed, from the USSR to the USA, areextremely similar. It is difficult to avoid the conclusion thatsomebody, upon the beginning of the process of reinforcedconcrete construction one or two generations ago, introducedthe loading test as a rule of thumb, and that its provisions werethen copied by others for lack of something better.

This study included load tests of slabs in nine existingbuildings and constructing 18 new concrete slab specimensand testing them in the laboratory. The laboratory testsincluded specimens intentionally constructed with defectiveconcrete. The test methods included a method of alternateloading, in which the load was applied and immediatelyremoved three times in succession. This was done up to thetotal load required by either British or American practice.

The following findings of this research were outlined inthe report.

3.6 Discussion of Results(i) First Criterion… in the laboratory load test the first criterion [that is, the useof the maximum deflection acceptance criterion (lt

2 /12,000h)]proved to be entirely safe, while, in the load tests on existingbuildings, … it proved to be entirely misleading. It was,however, consistently misleading, being always on the“unsafe” side. In other words, the actual deflections werealways smaller than those calculated in accordance withformula 3.4.1 [i.e. lt

2/12,000h]. We need not look far for thereason. The laboratory floor slabs were all freely supported,whereas the slabs in the buildings are all fixed. Formula 3.4.1[L2/20,000h] was established at a time when fixing reinforcingconcrete slabs was hardly known. Formula 3.4.1 thereforeprovides an adequate criterion for freely supported slabs, butwhere the slabs are fixed, actual deflections are muchsmaller. This points to the necessity and possibility for estab-lishing a formula analogous to 3.4.1 one which would takeinto account modern methods of reinforced concreteconstruction…



(ii) Second Criterion…the application of the second criterion in the building tests[i.e. use of deflection recovery criterion in the tests of slabsin existing buildings] gave entirely erratic results, sometimesgood and sometimes bad.

In the laboratory testing, only one slab showed on firstloading a recovery of more than 75%. This slab was deliber-ately constructed with low-strength concrete. All other slabsfailed this criterion on first loading. All slabs, whether up toor below strength requirements, showed adequate recoverieson second loading, while on third loading, the recovery waspractically complete.

The report goes on to state that it can therefore be said thatthe second criterion (that is, the deflection recovery require-ment) does not provide a means of judging the quality of theconcrete.

Generally speaking, even good concrete will fail on firstloading, while even bad concrete will pass on second andfurther loading.

This report contains an interesting commentary on the useof deflection recovery in load testing practice. The conclusionssection includes the following statements:

Even the worst concrete attains practically 100% recoveryon repeated loading... also, the data from our testing showsthat the permanent deformation due to creep and non-recov-ered elastic after-effect is negligible. Therefore the criterionof ‘recovery’ has no meaning.

Regarding use of maximum deflection as an acceptancecriterion, the following commentary is included in theconclusions of the report:

We have found that the criterion of ‘maximum deflection,’ ifcalculated in accordance with a formula applicable in thecase of freely supported beams, is suitable, and that thequality of concrete can thus be judged in accordance with themagnitude of E. If this is so, however, we must know thecorrect instantaneous elastic deflection, which is mostpronounced when the maximum percentage of recovery isattained. In accordance with the results of our research, weare, therefore, of the opinion that it might be possible to finda correct procedure for the loading test by performing‘alternate’ loadings up to the maximum load required by thetest, measuring the last recovered deflection and comparingthis with a calculated deflection taking into account theactual proportion of steel and concrete and the conditions offixing. It will then be necessary to specify a maximumdeflection, and the criterion would be whether this maximumdeflection is exceeded or not. Further research is required inconnection with this procedure in order to specify themaximum deflection for different cases of design, andespecially taking into account the use of high grade steel.

The information contained in this report, although over 50years old, is still pertinent to nearly all of the lingeringworldwide concerns regarding load testing practice.

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B.3.3 Report of Committee on Testing of Structures (Insti-tution of Structural Engineers 1964)—This report identifiedtwo types of load tests. The first was an acceptance test tocheck the behavior of a structure or part of a structure undera load equal to or greater than the known working load, so asto assess its adequacy for service; the second was a test todestruction to determine ultimate strength.

Regarding test load for an acceptance test, this reportindicates that the estimated dead load should be arbitrarilyincreased by an amount that should not exceed 10%. It isfurther indicated that the imposed load (that is, live load)should also be arbitrarily increased by not more than 25%.This would equate to a total test load TL = 1.10D + 1.25L.

The report contained the following statements relative tothese guidelines:

The above recommended increases of loadings are notintended to ensure some particular load factor against failurenor to test the structure to a specified proportional increase instress. The acceptance test is intended merely to demonstratethat the behaviour of the structure at working loads, or atslightly higher loads that might for some reason be appliedduring the life of the structure, is likely to be satisfactory.

The following additional guidelines are contained in thisdocument relative to load tests of reinforced concrete structures:

1. Duration of test loading is to be 8 hours.

2. Guidance for maximum allowable deflection during test:a. Proof of serviceability is the object of an acceptance

test, and the only requirement in regard to any deflectionor deformation is that it shall not exceed the appropriatepermissible amount that is either specified in thedesign standard or established by the engineer.

b. In buildings where finishes are to be applied after thedeformations due to dead load are substantiallycomplete, deformations due only to imposed load needbe considered when establishing permissible limits fromthe viewpoint of possible damage to finishes; (L/360)

c. In buildings it is also necessary to limit the total deflection(due to both dead and imposed loads) from the view-point of appearance; (L/250).

d. In structures where damage to finishes has not to beconsidered, and where appearance is not as critical as inbuildings, deflections due both to dead and to imposedloads may be greater than for buildings, and any limitshould be a matter for the engineer’s decision.

3. Recovery, measured 8 hours after load removal, equal toor greater than 75%.

4. Provision for retesting; after removal of the test imposedload, the recovery of deformation should be at least 75%. Ifthis requirement is not met, but the recovery is neverthelessnot less than 50%, the structure should be regarded as satis-factory if, on re-test, the recovery is at least 75%.

This document also introduces allowable crack widthacceptance criteria:

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The maximum widths of cracks at the working load shouldnot exceed 0.3 mm (0.012 in) for internal construction andnormal conditions of exposure; 0.2 mm (0.008 in) forexternal constructions and normal conditions of exposure; or0.1 mm (0.004 in) for aggressive conditions of exposure,whether for internal or external construction. Lower limitsmay be desirable for prestressed concrete structures.

B.3.4 ASTM Committee E6, Performance of Buildings:1965 to 1995—A special task group of ASTM Committee E6was formed in 1965 and worked for 8 years to address theissues associated with providing guidance for load testing ofexisting structures. The first results of that task force wereoutlined in a paper in 1975 (FitzSimons and Longinow 1975).While a good reference on the general aspects of load testingof all types of structures, little specific guidance was provided.

ASTM subsequently published ASTM E 196, “StandardPractice for Gravity Load Testing of Floors and Flat Roofs(ASTM E 196-95),” but that document also provided littlein the way of specific guidance for load testing of existingstructures.

B.3.5 Czechoslovak State Standard CSN 73 2030 (1977)—This document was produced as a result of a comprehensiveproject directed by Richard Bares, with the Institute ofTheoretical and Applied Mechanics, at the CzechoslovakAcademy of Science in Prague, Czechoslovakia. Barescontacted experts in many different countries, and he isconsidered to have produced one of the most comprehensivedocuments on load testing of structures at that time. This docu-ment was originally issued in 1969, but an English translationfrom 1977 was made available to the committee. Bares andFitzSimons (1975) provided a summary of the document.

Relevant highlights of this document include:

1. The purpose of a load test is to assess the actual behaviorof a structure or member through determination of its load-bearing capacity or usability in terms of magnitude of deflectionand cracking under applied loads;

2. Types of load tests:a. Proof tests to demonstrate the ability of a member or

structure to satisfy the given purpose in accordancewith design requirements, the suitability of a newconstruction method, or new construction materialsused;

b. Control tests to demonstrate the ability of a member orstructure to satisfy the given purpose in accordancewith design requirements that already have beenapproved; and

c. All other tests not intended exclusively for the assessmentof a single member or structure;

3. Each load test can be executed as follows:a. To failure of the structure or a portion of it to determine

its ultimate load-bearing capacity; orb. By test loads specified to prove the usability of the

structure or a portion of it with reference to its: (a)load-bearing ability; (b) rigidity (deflection); or (c)cracks (deformation);


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4. Age of structure—the test is carried out only after thestructure has attained the required properties, particularly thefull strength of the materials used, or after the termination ofsignificant creep or settlement of the structure, or both. In thecase of concrete structures, it is recommended that the testsbegin after 3 months;

5. Magnitude of superimposed test load—Specified as thequantity Z = 0.5L(1 + n), where n is a factor varying fordifferent structural materials from 1.1 to 1.4. For concretethe superimposed test load thus varies from 1.05L to 1.2L. Intesting for serviceability, the value of the test load is specifiedto be 1.0L.

6. Duration of loading: 24 hours for normal weight concretestructures;

7. Acceptance criteria: a. The load under which the structure has failed is the load

under which the structure has lost its ability for furtheruse due to one of the following causes:i. Complete failure of the structure or its part or

section or the rupture of reinforcement;ii. Loss of stability of the structure or its part or

member;iii. Local failure that continues to grow without any

increase in load;iv. The deformation increments under the same load

measured three times in succession at identicalintervals do not decrease;

v. The deformation increment due to the last loadingstate equals the sum of the deformations due to thefirst five equally high loading stages or exceeds it;

vi. The deflection equals or exceeds 1/50th of thespan length;

vii. In deformed concrete structures, the width of cracksequals or exceeds 1.5 mm (0.060 in.) providedthese cracks are at least 200 mm (8 in.) long;

viii.The failure of concrete structures by slanting cracksin the proximity of supports or point loads; or

ix. Loss of bond between reinforcement and concrete.b. The tested building structure is considered usable with

reference to its load-bearing ability if it has fulfilledsimultaneously the following conditions:i. The magnitude of permanent deformations does

not exceed 25% for reinforced concrete structures;ii. The state of failure due to the design load is stabi-

lized, while the width of cracks in concrete struc-tures does not exceed 0.3 mm (0.012 in.), if theyare protected against weather, and 0.2 mm (0.008 in.)if they are exposed to weather.

c. The tested building structure is considered usable withreference to its rigidity (deformation), if it satisfiessimultaneously the following conditions:i. The measured elastic deformations under test load

must not exceed the k multiple of the theoreticallydetermined value (varies between 1.1 and 1.2 forreinforced concrete);

ii. Total deflections or other total deformations understandard live load must not exceed the limit deflec-tions or deformations given in the respective stan-dards for the design and erection of building

ht American Concrete Institute

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structures and reduced according to the magnitudeand period of application of the load;

iii. Total deflections or other total deformations underthe test load must not exceed the limit deflectionsor deformations more than k times (varies between1.1 and 1.2 for reinforced concrete);

iv. A test structure of reinforced concrete is consid-ered usable with reference to the origin and devel-opment of cracks, if it satisfies simultaneously thefollowing conditions:1. The crack width under standard live load must

not exceed the values stipulated by the standardsfor the design of structures;

2. The distance between cracks under standard liveload must not exceed the values stipulated bythe standards for the design of structures;

3. The cracks do not appear under loads less than0.9 of the theoretically determined load for theoriginal of the first crack according to the theoryof elasticity; and

4. After the removal of the load, the cracks close toa width less than 1/3 of the prescribed value.

B.3.6 General Recommendation for Statical Loading Testof Load-Bearing Concrete Structures In Situ (RILEM TBS-2)(RILEM 1980)—The following are pertinent sections of thisdocument:

1. Loading tests are investigation processes to be carried outon buildings, load-bearing structures or parts with the aim ofobtaining empirical experimental data concerning their load-bearing capacity or suitability for the purpose intended.

2. The referenced and maximum value of the test load is tobe determined according to the purpose of the test. Suchpurposes might be:

a. To check serviceability by safety test;b. To define load-bearing capacity reserve (for example,

for structures of unknown load-bearing capacity);c. To check load-bearing capacity.

3. When testing serviceability, the reference value of testload is to be based on:

a. The useful and expected loads specified in standards;b. The useful and expected loads as indicated by the

designer;c. The values calculated from the load-bearing capacity

limit, deducting dead load;d. The load which gives rise to the deformation limits

permitted for the structure or the crack widths,reduced by the dead load.

4. It is suggested to apply a 1.4 load increasing factor forvariable useful loads, while for permanent useful loads a 1.2factor is most advisable.

5. The value of the test load should be increased if: the use ofthe building requires an unusually high safety factor; adecrease in load-bearing capacity with time is anticipateddue to such factors as corrosion or deterioration of materialproperties; the effects of shrinkage, creep and relaxation areimportant and should be considered; the structure will beexposed to extreme environmental factors such as large


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temperature variations; the effects of dynamic loads areimportant; the service live load exceeds twice the dead load.No quantitative guidance is provided in the document,however, on what additional increase is appropriate.

6. For tests to define the load-bearing capacity, the test load isto be determined by continuous processing and evaluating ofthe loading test results during the test. In this case, themaximum test load will be calculated from the load values thatdetermine the permitted ratio between permanent and totaldeformation, stabilization of deformations as well as the defor-mation limits of the structure and the permitted crack width.

7. If the aim of the load test is to establish the load-bearingcapacity (ultimate strength) of the structure, test loads will bedetermined from the ultimate strength calculated from thenominal yield strength of the steel in the structure as well asthe nominal concrete strength, taking into considerationstrength variability.

8. Minimum age of structure at time of test = 56 days.

9. Duration of maximum loading to be 16 hours.

10. If the aim of the load test is to define the actual load-bearing capacity limit of this structure, it is suggested that thestructure be subjected to a number of load and unloadingcycles, with ever increasing load magnitude, with half-hourincrements for loading and unloading, and half-hour waitingperiods between loading periods.

11. Failure criteria:a. The structure or any part of it has collapsed, fallen into

two or even more parts;b. The structure or any part of it has lost its stability;c. The local damage of the structure increases, spreads

without essential increase of loading;d. The deformation of the structure shows no decrease at

unchanged load, measured three times, after equalintervals;

e. At the last loading stage the extent of deformationreached or exceeded the full deformation that occurredduring previous stages when the same loads wereapplied;

f. Deflection equals or exceeds L/50;g. On the structure exposed to bending load, the crack

width, measured at 200 mm (7.87 in.) distances,amounts to a total of 1.5 mm (0.059 in.);

h. The extent of the diagonal cracks near the supports ofthe concrete structure reaches or exceeds the value initem ‘g’ above;

i. The structure is separated from the stiffening.

12. Acceptance criteria—In the absence of more rigorousprovisions, the structure tested is found suitable for service,if the following conditions are fulfilled:

a. None of the failure criteria exist;b. The residual deflections and deformations do not exceed

the following percentage values of total deflection.i. For new structures, at least 56 days old, when loaded

for the first time:1. For prestressed concrete structures 20%.2. For reinforced concrete structures 25%.--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

Concrete Institute er license with ACI etworking permitted without license from IHS

ii. For structures already used, previously exposed tofull loading, half of the above values are used.

iii. Structures from 28 to 35 days old may have valueshigher by 1.25:1. The remaining deflections reach 1.5 of the

former values as a maximum and the deflec-tions that remain after the unloading followingthe second load-bearing test are not greater thanhalf the percentages given for the first loadingtest and in the case of a possible third test 1/3 ofthe deflections remaining after the second test;

2. The measured deflections and deformations donot exceed 1.2 of the calculated values,provided that the true value of the elasticmodulus of the structure was used for the calcu-lating of deformations;

3. The curves showing deformation due to loadingare with good approximation linear or discon-tinuously linear, with definite break points andthe deformations became stabilized during theloading test.

c. The maximum crack width is within the limits stipulatedfor the materials and purpose of the structure;

d. The maximum deflections and other deformationsremain within the limits stipulated for the structureaccording to its intended use.

B.3.7 CSA Standard A23.3 (Canadian Standards Associa-tion 1994)—Section 20.3 of this document addresses“General Requirements for Load Tests.” It contains thefollowing relevant items:

1. Age of structure should be 28 days or more at time oftesting.

2. Superimposed dead loads: A load to simulate the effect ofthe portion of the dead loads not already present shall beapplied 24 hours before the application of the test load andshall remain in place until all testing has been completed.

3. Test load:a. When an entire structural system in doubt is load tested

or an entire questionable portion of a system is loadtested, the test load shall be 90% of the factored loads,Mf , Vf , and Pf . When only a portion of a structuralsystem in doubt is tested and the results of the tests aretaken as representative of the structural adequacy ofother untested portions of the system, the test loadshall be equal to the factored loads Mf , Vf , and Pf .

b. The superimposed test load shall be applied in not lessthan four approximately equal increments withoutshock to the structure and in a manner to avoid archingof the load materials.

c. The test load shall be left in place for 24 hours.

4. Acceptance criteria:a. If the portion of the structure tested fails or shows

visible indications of impending failure, it shall beconsidered to have failed the test.

b. Deflection recovery: For load tests of flexural systemsor members for moment resistance, the requireddeflection recovery values are specified as follows:i. Nonprestressed members:


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1. First test 60%2. Retest 75%

ii. Prestressed members: 80%

This document has considerable similarity to ACI 318-05requirements for load testing. Examination of the CSA testloads and the CSA factored loads reveals that the ACI andCSA factored loads are not substantially different. The CSAtest loads are as follows:

TL = 0.9(1.25D + 1.5L) = 1.125D + 1.35L

when the entire structural system or entire portion of asystem is tested.

TL = 1.25D + 1.5L

when only a portion of a structural system is tested and isintended to be representative of the untested portion of thestructure.

In addition, the CSA provisions do not include a maximumacceptable deflection for a load test. Only deflectionrecovery criteria are included.

B.3.8 Guidance for Engineers Conducting Static LoadTests on Building Structures (BRE 1995)— This documentcontains the following guidance for testing concrete structuresfor serviceability.

1. The purpose of this type of testing is to establish whetherthe structure is likely to perform satisfactorily in service.Both long-term deformations under permanent dead load andshort-term deformations due to imposed loads need to bewithin acceptable limits, and the structure must be able tocarry its full service loading safely.

2. Where the test load is not specified in the relevant code ofpractice or is not applicable to the particular circumstancesof the structure being considered, the test load may be chosenas the maximum the structure should sustain withoutsuffering permanent deformation or damage, or TL = 1.25D+ 1.25L, whichever is less.

3. The maximum applied load should be left on the structureuntil it has in effect come to rest. A period of 24 hours islikely to be sufficient for most structures.

4. Acceptance criteria:a. The maximum deflection recorded does not exceed that

given in the relevant code of practice or that specifiedfor the structure.

b. For concrete structures that have been bedded-in byreapplying the full test load several times, the recovery24 hours after removal of the load would be expectedto exceed 90%.

c. Existing cracking and deformation do not extendsignificantly during the test.

d. The structure shows no other signs of damage ordistress as a result of the test cycle.

ght American Concrete Institute ed by IHS under license with ACI roduction or networking permitted without license from IHS

Regarding the interesting aforementioned concept of“bedding-in,” the following information is presented in thisreport:

1. Depending on the magnitude of the full test load, loadhistory, type of construction, and structural material,bedding-in loads may be desirable. The object of applyingbedding-in loads is to settle the structure on its supports andrelease any frictional restraints incorporated duringconstruction;

2. Bedding-in loads should be applied and removed in atleast five increments, with deformations being monitored. Ingeneral, the magnitude of bedding-in load should not exceedthe intended future service loading. The structure can beconsidered to be satisfactorily bedded-in when it has recoveredto its original position (+/– 10%) after a loading cycle;

3. For concrete components to be taken beyond their serviceloading, the full test load is itself likely to produce slightdegradation of the component. In these circumstances, itmay be necessary to reapply the full test load several timesuntil a repeatable response is obtained between successiveloadings.

This information echoes findings of the Israeli research reportand is of significance in regard to proposals to adopt or allowcyclic load testing of concrete structures under ACI 318.

B.3.9 2003 International Building Code (InternationalCode Council 2003)—The 2003 International Building Codecontains guidance on conducting load tests on existingbuilding structures. The following is a summary of the majorprovisions of this key building code:

1. Whenever there is a reasonable doubt as to the stability orload-bearing capacity of a completed building, structure orportion thereof for the expected loads, an engineering assess-ment shall be required. The engineering assessment shallinvolve either a structural analysis or an in-situ load test, or both.

2. The IBC refers to material standards for provisions inconducting load tests. This includes ACI 318-05.

3. For structures not covered by ACI 318-05 or any othermaterial standard listed in the IBC, the following minimumtest criteria are outlined:

a. The test load shall be equal to two times the unfactoreddesign loads;

b. Under the design load, the deflection shall not exceedthe limitations specified in Section 1604.3. Thosedeflection limits, for a superimposed live load only,vary from L/180 to L/360, and are based on service-ability limit states only;

c. Within 24 hours after removal of the test load, thestructure shall have recovered not less than 75% of themaximum deflection; and

d. During and immediately after the test, the structureshall not show evidence of failure.

B.3.10 Italian codes—According to the Italian buildingcode, the design and construction of a new building must beverified by an independent professional engineer who has


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been licensed for at least 10 years. In most cases, as part ofthe “threshold inspection,” the engineer requires that a loadtest be conducted before the public use of the structure. Thesame stipulation applies to existing buildings when there is aneed to assess their structural performance with respect tobuilding code changes or changes in use.

In contrast to the U.S. construction practice where floorsare generally made of cast-in-place reinforced concrete slabswith likely uniform and known properties in both directions,it is common practice in Italy to have floors made of cast-in-place or precast reinforced concrete joists spaced by voidedclay tiles, then topped with a thin overlay of concrete reinforcedwith a steel mesh to redistribute the load. It is clear that insuch a structural system it is rather difficult to determine howloads distribute because of uncertainties in the boundaryconditions as well as in the transverse stiffness. For thesereasons, through the years researchers and practitioners havedeveloped methods to determine how to compute equivalenttest patch loads to simulate uniformly distributed loads.

Current practice in Italy (Lombardo and Mirabella 2004)shows that an equivalent force to substitute for the uniformlydistributed load may be calibrated based on the knowledge ofthe deflection response of the member(s) and the surroundingstructure. The most common method to determine an equiva-lent patch load is to determine two coefficients k1 and k2 thattake into account the transverse and longitudinal redistributionof the load, respectively. Before conducting a load test, suchcoefficients can be computed experimentally and then usedto determine the appropriate value of the concentrated testload to simulate the uniformly distributed loads used fordesign. The method is based on the deflection response in thetwo perpendicular directions of the flooring system to asmall concentrated load, usually lower than the service loads(pilot test load). Based on the longitudinal deflectionresponse, it is possible to calibrate the coefficient thataccounts for the degree of fixity at the slab boundaries. Sucha coefficient is usually 1.0 when the fixity of the restraints atthe supporting beam locations is that of a perfect clamp. Thetransverse deflection response accounts for the participationof neighboring joists.

B.3.11 Recommended Practice for In-Situ Monitoring ofConcrete Structures by Acoustic Emission (NDIS 2421)(Japanese Society for Nondestructive Inspection [JSNDI]2000)—This document is thought to be unique in that it is thefirst standardized document that makes use of the acousticemission (AE) technique for the inspection and evaluation ofreinforced concrete structures. The document incorporatesfour related codes: description of functions and performanceon AE devices (NDIS 2106 [JSNDI 1997]); calibration ofAE sensors by the reciprocal method (NDIS 2109 [JSNDI1991]); evaluation method for the deterioration of AE sensorsensitivity (NDIS 2110 [JSNDI 1997]); and recommendedpractice for the continuous AE monitoring of pressurevessels (NDIS 2419 [JSNDI 1997]). The recommendedpractice came about in Japan because of the large number ofbridges that are reaching their intended service lives coupledwith the need for evaluation of structures after extremeevents, such as earthquakes. The practice notes aging,

n Concrete Institute
nder license with ACI License

fatigue, heavy traffic loads, chemical reactions, and disastersas events or environments that lead to a need for evaluationbefore repair and rehabilitation. Before this document, theonly standardized application of the AE technique to in-service structures had been to pressure vessels.

The stated purpose of this document (NDIS 2421) is tostandardize existing techniques to estimate the degree ofdamage through in-place monitoring. The document addressesboth long-term monitoring and short-term monitoringthrough load testing. The recommended practice consists of11 chapters. The chapters entitled “Monitoring System” and“Tests and Evaluation” are described as follows:

Monitoring system—This chapter addresses amplification,parameters to be measured, duration of measurement andanalysis, and the type of analysis to be used including trendanalysis, distribution analysis, correlation analysis, andlocation analysis. The signal-to-noise ratio is noted as importantto the analysis, and acceptable levels are established. Thetreatment of noise, selection of an appropriate thresholdlevel, postanalysis of the data, dimensions of the sensor arrayto be used, and the frequency range of the sensors to be usedare described. A frequency range of 20 to 100 kHz is recom-mended to limit attenuation.

Test and evaluation—This chapter addresses thedifferentiation between AE signals because of service levelloadings and those that are representative of damage and notobserved in service conditions. It further discusses monitoringthat is performed continuously or routinely, and sometimestemporarily after disasters such as earthquakes.

The deterioration process of the structure is estimatedthrough the following AE parameters:

1. Sudden increase of AE activity normally detected bycounts, hits, and events;

2. Variation of such AE parameters as RMS, energy, andamplitude distribution;

3. Clustering and concentration of AE locations; and4. AE activity under cyclic loading.The document notes that through sudden increases in AE

activity, the deterioration process, and often impendingfailure, can be estimated. One example of deterioration andits relation to AE activity through the freezing-and-thawingprocess is given.

In regard to loading of structures, the rate process theoryis described. The probability function of AE occurrencefrom a stress level is formulated as a hyperbolic function. Arelationship between the number of total AE events (N) andthe stress level is given. The change of amplitude distributionis also noted to be useful. By applying AE location procedures,moment tensor analysis is used to define tensile or shearcracks and to determine crack orientation. In direct relationto controlled load testing for the evaluation of reinforcedconcrete structures, the Kaiser effect (a lack of or significantlyreduced acoustic emission before the previously appliedmaximum load) is described in detail. The relationshipbetween crack opening and the presence of the Kaiser effectin reinforced concrete beams has been reported previously.Further documentation of this effect has been reported under--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---


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truck loading of harbor structures. In relation to the Kaisereffect, two parameters are proposed:

1. Ratio of load at the onset of AE activity to previous load:

load ratio = load at onset of AE activity under the repeated loading/previous load

2. Ratio of cumulative AE activity under unloading to thatof previous maximum loading cycle:

calm ratio = the number of cumulative AE activity during unloading/total AE activity at the previous maximum

loading cycle

pyright American Concrete Institute ovided by IHS under license with ACI reproduction or networking permitted without license from IHS

Based on these parameters, a criterion to evaluate damageis plotted schematically as calm ratio versus load ratio; andthe damage is divided into heavy, intermediate, and minordamage. This approach has been applied to laboratoryspecimens with crack mouth opening displacement gagesfor correlation with the AE activity.

In regard to load testing and evaluation with acousticemission in the United States, there are currently codesrelated to: 1) tanks and pressure vessels—ASME RTP-1[ASME 2004] and ASME Section X [ASME 2004]); and,2) aerial devices (that is, manlifts) (ASTM F 914). In thefield of civil structures, AE-based techniques are currentlygaining favor, but are not widely used in practice. Until somestandard guidelines are developed in the United States, it willdifficult for AE to become accepted.


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As ACI begins its second century of advancing concrete knowledge, its original chartered purposeremains “to provide a comradeship in finding the best ways to do concrete work of all kinds and inspreading knowledge.” In keeping with this purpose, ACI supports the following activities:

· Technical committees that produce consensus reports, guides, specifications, and codes.

· Spring and fall conventions to facilitate the work of its committees.

· Educational seminars that disseminate reliable information on concrete.

· Certification programs for personnel employed within the concrete industry.

· Student programs such as scholarships, internships, and competitions.

· Sponsoring and co-sponsoring international conferences and symposia.

· Formal coordination with several international concrete related societies.

· Periodicals: the ACI Structural Journal and the ACI Materials Journal, and Concrete International.

Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACImembers receive discounts of up to 40% on all ACI products and services, including documents, seminarsand convention registration fees.

As a member of ACI, you join thousands of practitioners and professionals worldwide who share acommitment to maintain the highest industry standards for concrete technology, construction, andpractices. In addition, ACI chapters provide opportunities for interaction of professionals and practitionersat a local level.

American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701

www.concrete.org

American Concrete Institute®

Advancing concrete knowledge



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The AMERICAN CONCRETE INSTITUTE

was founded in 1904 as a nonprofit membership organization dedicated to publicservice and representing the user interest in the field of concrete. ACI gathers anddistributes information on the improvement of design, construction andmaintenance of concrete products and structures. The work of ACI is conducted byindividual ACI members and through volunteer committees composed of bothmembers and non-members.

The committees, as well as ACI as a whole, operate under a consensus format,which assures all participants the right to have their views considered. Committeeactivities include the development of building codes and specifications; analysis ofresearch and development results; presentation of construction and repairtechniques; and education.

Individuals interested in the activities of ACI are encouraged to become a member.There are no educational or employment requirements. ACI’s membership iscomposed of engineers, architects, scientists, contractors, educators, andrepresentatives from a variety of companies and organizations.

Members are encouraged to participate in committee activities that relate to theirspecific areas of interest. For more information, contact ACI.

www.concrete.org

Load Tests of Concrete Structures:Methods, Magnitude, Protocols, and Acceptance Criteria



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