performance of 1/3-scalemodel precast concrete beam

PB9122570 11111111111111111111111111111111 I

------)

NISTIR 4589

June 1991

Geraldine S. CheokH. S. Lew

,( REPRODUCED BY: MTIS.'Ii u.s. Departmenl of Commerce ~._-

I, National Technicallnronnatlon Service I'l ' Springfield, Virginia 22161 J

Performance of 1/3-Scale Model Precast

Concrete Beam-Column Connections Subjected

to Cyclic Inelastic Loads-Report No.2

U.S. Department of CommerceRobert A. Mosbacher, SecretaryNational Institute of Standards and TechnologyJohn W. Lyons, DirectorBuilding and Fire Research LaboratoryGaithersburg, MD 20899

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ABSTRACT

Results are presented from the experimental test program on precast concrete beam-column connectionssubjected to inelastic cyclic loads being conducted at the National Institute of Standards and Technology.This report is the second in a series and covers the test results from Phase II of a three phase program.The objective of the test program is to develop an economical moment resistant precast beam-columnjoint for high seismic zones.

Test specimens are 1/3-scale models of a prototype interior concrete beam-column connection. The 1985UBC design criteria for seismic Zones 2 and 4 were used. Six specimens were tested. The experimentalvariables include the location of the post-tensioning force and the type of post-tensioning tendons used.Comparisons of the performance among these specimens are made. Comparisons with the monolithicspecimens (Phase I [Ref. 1]) are also presented. These comparisons are made based on the failuremode, energy absorption characteristics, strength and ductility of the connection.

KEY WORDS: beam-columns; concrete; connections; cyclic loading; ductility; energy absorption; joints;moment-resistance; post-tensioning; precast concrete.

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ACKNOWLEDGEMENT

The authors would like to extend their thanks to the individuals who contributed to this project. Theassistance of the laboratory staff for the Center of Building Technology especially that of Mr. Frank Rankinis gratefully acknowledged. Also, the authors would like to express their thanks to the advisory committeefor providing technical guidance throughout the project. Members of the steering committee include Dr.Robert Englekirk, Dr. S. K. Ghosh, Mr. Daniel Jenny, Mr. Paul Johal, Dr. Nigel Priestley. The assistanceof Ms. Suzanne Nakaki in prOViding the design of the test specimens is also much appreciated.

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TABLE OF CONTENTS

Page

List of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ix

List of Figures xi

4.0 DISCUSSION OF TEST RESULTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63

5.0 SUMMARY AND CONCLUSIONS 73

2.0 SPECIMEN DESIGN, CONSTRUCTION AND TEST PROCEDURE 5

3.0 TEST OBSERVATIONS AND RESULTS 17

INTRODUCTION .

1.1 General .1.2 Summary of Phase I Results .

2.1 Specimen Design 52.2 Material and Construction 82.3 Instrumentation and Test Procedure 14

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4.1 Displacement Ductility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 634.2 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 644.3 Failure Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 654.4 Energy Absorbed 664.5 Reinforcing Bar Yield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71

5.1 Summary 735.2 Conclusions 73

3.1 Precast Concrete Specimens C-P-Z4 and D-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . .. 173.2 Precast Concrete Specimens E-P-Z4 and F-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . .. 343.3 Precast Concrete Specimens A-P-Z2 and B-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48

References i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 77

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Table

List of Tables

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2.1 Specimen Description 82.2 Steel Properties .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3 Concrete and Grout Strengths 102.4 Prestress Losses ,......... 12'2.5 Load Cell Readings After Post-Tensioning 144.1 Yield Displacement and Displacement Ductility " " . . . . . . . . . . . . . . . .. 634.2 Measured and Calculated Ultimate Moments 654.3 Cumulative Energy Absorbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 714.4 Reinforcing Bar Yield Length 72

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Figure

List of Figures

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1.1 Reinforcement details for monolithic Zone 2 specimens. . .1.2 Reinforcement details for monolithic Zone 4 specimens

and precast concrete specimens A & B. . .2.1 Reinforcement details for precast concrete Zone 4 specimens 62.2 Reinforcement details for precast concrete Zone 2 specimens .2.3 Steel cages for specimen C-P-Z4 and D-P-Z4 .2.4 Steel cages for A-P-Z2 and B-P-Z2 .2.5 Jacking assembly for precast concrete Zone 4 specimens .2.6 Set-up for post-tensioning precast concrete Zone 2 specimens .2.7 Boundary conditions for the test specimens .2.8 Test set-up and test facility .3.1 Loading sequence for specimens C-P-Z4 through F-P-Z4 .3.2 Crack pattern for specimen C-P-Z4 at 4 ~ .3.3 Opening between the beam and construction joint at 4 ~ .3.4 Crack 'pattern for C-P-Z4 at 6 ~ .3.5 Crus~lng of the beam at 6 ~ - C-P·Z4 .3.6 Opening between the beam and column at 6 ~ - C-P-Z4 .3.7 Beam damage at 8 l1" - C-P-Z4 .3.8 Speci,:"en C-P-Z4 at (ailure - 12 ~ .3.9 Crushl~g of beams at 12 ~ - C-P-Z4 .3.10 Opening between beam and column - C-P-Z4 .3.11 Specimen D-P-Z4 at failure - 12 ~ .3.12 Hysteresis curves for C·P-Z4 .3.13 Hysteresis curves for D-P-Z4 .3.14 Energy absorbed per cycle by specimens C-P-Z4 and D-P-Z4 .3.15 Top northeast reinforcing bar strains· C-P-Z4 .3.16 Bottom northeast reinforcing bar strains - C-P-Z4 .3.17 Top northwest reinforcing bar strains· C-P-Z4 .3.18 Bottom northwest reinforcing bar strains - C-P-Z4 .3.19 Top southeast reinforcing bar strains - C-P-Z4 .3.20 Bottom southeast reinforcing bar strains - C-P-Z4 .3.21 Top southwest reinforcing bar strains - C-P-Z4 .3.22 Bottom southwest reinforcing bar strains· C-P-Z4 .3.23 Top northeast reinforcing bar strain - D-P-Z4 .3.24 Bottom northeast reinforcing bar strains - D-P-Z4 .3.25 Top northwest reinforcing bar strains - D-P-Z4 .3.26 Bottom northwest reinforcing bar strains - D-P-Z4 .3.27 Top southeast reinforcing bar strains - D-P-Z4 .3.28 Bottom southeast reinforcing bar strains - D-P-Z4 .3.29 Top southwest reinforcing bar strains - D-P-Z4 .3.30 Bottom southwest reinforcing bar strains - D-P-Z4 I •••••••••••••••••••••••••••••••

3.31 Shear cracks ~n F-P-Z4 at 4 ~ .3.32 Shea~ cracks In E-P-Z4 at 4 fly " .3.33 Openl~g between beam and column at 4 ~l F-P-Z4 .3.34 Crushln~ of beam at 4 ~. F-P-Z4 .3.35 Connection F-P-Z4 at 8 ~ .

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111315151718181919202121222223242425262627272828292930303131323233333435353637

3.36 Open.ing between the ~e!am and column at 12 ~I F-P·Z4 . . . . . . . . . . . . . . . . . . . . . . . . .. 373.37 Spec~men F-P-Z4 at fal.lure - 12 ~ 383.38 Specimen E·P-Z4 at failure· 12~ 383.39 Hysteresis curves for E-P-Z4 , 393.40 Hysteresis curves for F-P·Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 393.41 Energy absorbed by specimens E-P-Z4 and F-P-Z4 403.42 Top northeast reinforcing bar strains - E-P·Z4 , 403.43 Bottom northeast reinforcing bar strains - E-P-Z4 413.44 Top northwest reinforcin~1 bar strains· E-P-Z4 413.45 Bottom northwest reinforcing bar strains· E-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . .. 423.46 Top southeast reinforcin~1 bar strains - E-P·Z4 423.47 Bottom southeast reinforcing bar strains· E-P-Z4 , 433.48 Top southwest reinforcinn bar strains - E-P-Z4 433.49 Bottom southwest reinfon:::ing bar strains - E-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 443.50 Top northeast reinforcing bar strains - F-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 443.51 Bottom northeast reinforcing bar strains· F-P-Z4 453.52 Top northwest reinforcing' bar strains - F-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 453.53 Bottom northwest reinforcing bar strains - F-P-Z4 463.54 Top southeast reinforcing bar strains - F-P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 463.55 Bottom southeast reinforcing bar strains - F-P-Z4 473.56 Top southwest reinforcin~, bar strains· F-P-Z4 473.57 Bottom southwest reinforcing bar strains - F·P-Z4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 483.58 Loading sequence for spElcimens A-P-Z2 and B-P-Z2 493.59 Cr~ck p~ern at ~ ~ - A-IP-Z2 503.60 JOint region .at failure, 4 Av- A-P-Z2 513.61 Beam. crushing at 4 ~ - A-P-Z2 513.62 O~enlng .betwee~ beam and column at 4 ~ - A-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 523.63 JOint region at failure, 4 .:l~~ B-P-Z2 523.64 Hysteresis curves for A-P-12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 533.65 Hysteresis curves for B-P-:Z2 " 533.67 Top northeast reinforcing bar strains - A-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 553.68 Bottom northeast reinforcing bar strains - A-P-Z2 553.69 Top northwest reinforcing bar strains - A-P-Z2 563.70 Bottom northwest reinforcing bars strains • A-P-Z2 563.71 Top southeast reinforcing bar strains - A-P·Z2 573.72 Bottom southeast reinforcing bar strains - A-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 573.73 Top southwest reinforcing bar strains - A-P·Z2 583.74 Bottom southwest reinforciing bars strains - A-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 583.75 Top northeast reinforcing bar strains - B-P-Z2 .. " '. . . . . . . . . . . .. 593.76 Bottom northeast reinforcing bar strains - B-P-Z2 593.77 Top northwest reinforcing :bars strains - B-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 603.78 Bottom northwest reinforcing bar strains - B-P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . .. 603.79 Top southeast reinforcing Ibar strains - B-P-Z2 613.80 Bottom southeast reinforcing bar strains - B-P-Z2 . . . . . . . . . . .. . . . . . . . . . . . . . . . . .613.81 Top southwest reinforcing bar strains - B-P-Z2 623.82 Bottom southwest reinforcing bar strains - B·P-Z2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 624.1 Comparison of cyclic energy absorbed to 6 ~, cycle 3 674.2 Cyclic energy absorbed by precast Zone 4 specimens " 684.3 Cyclic energy absorbed by :~one 2 specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 694.4 Comparison of the cumulative energy absorbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70

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1.0 INTRODUCTlON

1.1 General

A study of the behavior of 1/3-scale model precast concrete beam-column connections subject to cyclicinelastic loading was initiated at the National Institute of Standards and Technology (NIST) in 1987. Theobjective of the experimental program was to develop recommended guidelines for the design of aprecast concrete beam-column connection for regions of high seismicity. A project steering committeeconsisting of individuals from the Prestressed/Precast Concrete Institute (PCI), Portland CementAssociation (peA), academia and private sector is working with NIST throughout the test program.

The test program consisted of three phases. Phase I was an exploratory phase where four monolithicbeam-column connections and two precast concrete specimens were tested. The results of the monolithicspecimens served as a reference for the precast concrete tests. Phase II of the program involved thetesting of six (6) precast specimens. Several methods of improving the energy dissipation characteristicsof the precast concrete connection were explored. In Phase III, means of improving the hystereticbehavior of the precast concrete connection both analytically and experimentally will be examined.

Phase I results were reported in Reference 1, and this report presents the results of Phase II of the testprogram. Included in Reference 1 is a more detailed introduction of the test program and a literaturereview of related studies. A summary of the test results from Phase I is presented in the following section.

1.2 Summary of Phase I Results

In Phase I of the precast concrete concrete beam-column connection study at NIST, six (6) specimenswere tested. Two of the specimens were monolithic concrete connections designed to UBC (1985)seismic Zone 2 criteria (A-M-Z2 and B-M-Z2). The other four specimens were designed to UBC (1985)seismic Zone 4 criteria. Two of the Zone 4 specimens were monolithic specimens (A-M-Z4 and B-M-Z4)while the remaining two were precast concrete with post-tensioned beam-column connections (A-P-Z4 andB-P-Z4). The nomenclature for the specimens is as follows:

1. First character: Specimen Name - A, B, C, .... Specimens A & B, C & 0, E & F, etc. areidentical specimens and form one set.

2. Second character: M = Monolithic, P = Precast3. Third & fourth characters: Z2 = Zone 2, Z4 = Zone 4.

The precast concrete elements were connected by two 25 mm (1.0 in) diameter post-tensioning barshaving an ultimate strength of 1034 MPa (150 ksO. Figs. 1.1 and 1.2 show the reinforcement details forthe specimens tested in Phase I. The inch wide construction joint between the beam and column wasfilled with a fiber reinforced grout and the post-tensioning ducts were grouted after tensioning.Commercially available pre-mixed grout and straight steel fibers 19 mm (0.75 in) long were used. Resultsfrom the monolithic tests are used as a benchmark reference for both present and future precast concretetests.

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@ 51 mm (2 in) O.C.

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IBEAM CROSS SECTION COWMN CROSS SECTION

Fig. 1.1 Reinforcement details for monolithic Zone 2 specimens. I

25 mm (1 In) Posl-tensloning bat38 mm (1.5 in) Corrugated duel

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Fig. 1.2 Reinforcement details for monolithic Zone 4 specimensand precast concrete specimens A & B.

BEAM CROSS SECIDN COI..U~CROSS SECIDN

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Failure of the monolithic Zone 2 specimens occurred in the joint region due to a combination of high jointstresses and inadequate confinement. The monolithic Zone 4 specimens failed as a result of beamhinging and deterioration. Failure of the post-tensioned specimens was characterized by plasticelongation, 12.7 mm (0.5 in), of the post-tensioning bars and crushing and spalling of the concrete coverin the beams. Joint shear stresses for the Zone 4 specimens were below the ACI-ASCE Committee 352recommended value of 20~ (f~ in psi).

The ultimate displacement ductilities for the monolithic Zone 2 specimens were 6 (see section 4.1). Theseductilities corresponded to story drifts of 4.1 % and 4.3%. The ultimate displacement ductility for the posttensioned specimens were higher than for their companion monolithic specimens - 10 vs. 6. However,since the post-tensioned specimens were stiffer than the monolithic specimens, the story drift at failurefor the Zone 4 post-tensioned and monolithic specimens were almost identical. The story drifts at failurefor the Zone 4 specimens ranged from 3.0% - 3.4%. The post-tensioned specimens were approximatelytwice as stiff as the monolithic Zone 4 specimens and fives times as stiff as the monolithic Zone 2specimens.

The post-tensioned connections were slightly stronger than the monolithic specimens. The ultimate beammoments were on average 18% greater than the calculated moments for the post-tensioned specimensand 13% greater for the monolithic Zone 4 specimens. The monolithic Zone 2 specimens achievedmaximum measured beam moments that were on average 8% greater than the calculated moment.

When comparing the energy absorbed per cycle, the behavior of the post-tensioned specimens was moresimilar to the monolithic Zone 2 specimens than to the monolithic Zone 4 specimens. On a per cyclebasis, the post-tensioned specimens absorbed about 30% of the energy absorbed by the monolithic Zone4 specimens. However, since the post-tensioned specimens achieved higher displacement ductilities thanthe monolithic specimens, the average of the cumulative energy absorbed up to failure by the posttensioned specimens was approximately 80 % of that for the monolithic Zone 4 specimens. The averageof the cumulative energy absorbed up to failure by the monolithic Zone 2 specimens is about 33% of thatabsorbed by the monolithic Zone 4 specimens.

Based on the results of the Phase I test program, it would appear that a post-tensioned precast concretebeam-column connection is a candidate for use in high seismic regions. However, the energy dissipationcharacteristics for this type of precast connection need to be improved and will thus be the focus ofPhase 11 of the test program.

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2.0 SPECIMEN DESIGN, CONSTRUCTION AND TEST PROCEDURE

2.1 Specimen Design

The results of Phase I tests indicated that a post-tensioned connection designed based on the 1985 UBCseismic Zone 4 criteria was as strong as the monolithic Zone 4 specimens. However, the cumulativeenergy absorbed by the precast concrete Zone 4 specimens was 20% lower and the per cycle energyabsorbed by the precast concrete Zone 4 specimens was 70% lower than the monolithic Zone 4specimens. It was determined through discussions with the project steering committee that a possiblemethod of improving the energy absorption characteristics of the precast concrete connection was tomove the post-tensioning bars closer towards the beam center. By doing this, the post-tensioningbars/prestressing strands would experience less strain and would therefore retain their post-tensioningforce for a longer period.

Also, as mentioned in Ref. 1, prestressing strands are used more commonly than post-tensioning barsin practice due mainly to the lengths required when post-tensioning several bays at a time. It was alsofelt that the use of six strands instead of two post-tensioning bars would help the energy absorptioncharacteristics. This was because of a more evenly distributed load and increased bond area with sixstrands as opposed to two bars. As a result, two sets of precast concrete Zone 4 specimens were tested.Post-tensioning bars were used to connect one set of specimens while prestressing strands were usedin the other set. In both sets, the centroid of the steel was moved closer to the beam centroid. Inaddition, one set of precast concrete Zone 2 specimens was constructed and tested.

The Phase II specimens were designed similarly to the Phase I precast concrete specimens. The requiredamount of post-tensioning steel was computed so that the strength of the precast concrete connectionwas as strong as the monolithic concrete connection. Reinforcement details for the precast columns, bothZones 2 and 4, were the same as those of the corresponding monolithic specimens. The reinforcementdetails for the Zone 4 precast concrete beams were identical to those of the Phase I precast concretespecimens except for the location of the post-tensioning bars/prestressing strands. Fig. 2.1 shows thereinforcement details for the precast concrete Zone 4 specimens and Fig. 2.2 shows the reinforcementdetails for the precast concrete Zone 2 specimens. The reinforcing bars located in the corners of the tiesin the beams were used mainly to hold the ties together. The main resistance to the applied loads wasprovided by the post-tensioning bars/prestressing strands. Figs. 2.3 and 2.4 show the steel cages for theZone 4 and Zone 2 specimens, respectively.

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BEAM GROSS SECTION COLUMN CROSS SECTION IFig. 2.1 ReinfOircement details for precast concrete Zone 4 specimens. I

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COLUMN cross SECTION

IFig. 2.2 Reinforcement details for precast concrete Zone 2 specimens.

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Fig. 2.4 Steel cages for A-P-Z2 and B-P-Z2.

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Fig. 2.3 Steel cages for specimen C-P-Z4 and D-P-Z4.

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2.2 Material and Construction

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A summary of the specimens teBted to date (Phase I and II) is given in Table 2.1.

The non-prestressed reinforceme~nt conformed to ASTM A706/A 706M requirements. The post-tensioningbars used conform to ASTM A-7:22 requirements and the low relaxation prestressing strands conform toASTM A-416. The ties and crossties were made from smooth wire. As with the Phase I specimens, thedesign concrete strength was 34.5 MPa (5000 psi). Material properties are given in Tables 2.2 and 2.3.

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Description

Precast Zone 4 specimens. Post-tensionedwith 6 prestressing strands. Steel centroidlocated 102 mm (4.0 in) from beamtop/bottom.

Precast Zone 2 specimens. Post-tensionedwith 4 prestressing strands located 63 mm(2.5 in) from beam top/bottom.

Monolithic Zone 2 specimens. Used as areference for precast Zone 2 specimens.

Monolithic Zone 4 specimens. Used as areference for precast Zone 4 specimens.

Precast Zone 4 specimens. Post-tensionedwith 2 post-tensioning bars located 138 mm(5.5 in) from beam top/bottom.

Precast Zone 4 specimens. Post-tensionedwith 2 post-tensioning bars located 89 mm(3.5 in) from beam top/bottom.

Table 2.1 Specimen Description.

Specimens

E-P-Z4 & F-P-Z4

A-P-Z2 & B-P-Z2

A·P·Z4 & B-P-Z4

C-P-Z4 & D-P-Z4

A-M-Z4 & B-M-Z4

A-M·Z2 & B-M-Z2

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Test Phase

The construction of the precast concrete specimens was similar to construction of the precast concretespecimens in Phase I. As shown in Figs. 2.3 and 2.4, the specimens were cast on their sides. A 25 mm(1.0 in) wide construction joint between the beam and column was filled with a fiber reinforced grout. Thefibers used were 19 mm (0.75 in) long straight steel fibers. Roughening of the beam and column surfacesto approximately 6 mm (0.25 in) amplitUde was done prior to post-tensioning the precast concreteelements. As in Phase I, corrugated ducts were used. The initial beam prestress was 10.5 MPa (1.5 ksi)and 7.0 MPa (1.0 ks~ for the preicast concrete Zone 2 and Zone 4 specimens, respectively.

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Table 2.2 Steel Properties.

Specimen tv MPa [ksi] tu MPa [ksi]

Wire #3 #4 PT Wire #3 #4 PT

C-P-Z4 574 466 419 10248 627 620 669 1103

[83] [68] [61 ] [149] [91 ] [90] [97] [160]

D-P-Z4 574 466 419 10248 627 620 669 1103

[83] [68] [61 ] [149] [91 ] [90] [97] [160]

E-P-Z4 543 512 419 1824b 593 772 669 1917

[79] [74] [61] [265] [86] [112] [97] [278]

F-P-Z4 543 512 419 1824b 593 772 669 1917

[79] [74] [61 ] [265] [86] [112] [97] . [278]

A-P-Z2 543 466 419 1824b 593 510 669 1917

[79] [68] [61 ] [265] [86] [74] [97] [278]

1717c 1917

[249] [2781

8-P-Z2 543 466 419 1824b 593 510 669 1917

[79] [68] [61 ] [265] [86] [74] [97] [278]

1717c 1917

[247] [278]

a 25 mm (1.0 in) post-tensioning bar.b 11 mm (0.44 in) prestressing strand at 1% strain.c 13 mm (0.5 in) prestressing strand at 1% strain.

9

Table 2.3 Concrete and Grout Strengths.

l' Duet Grout Joint GroutcSpecimen MPa [psi) MPa [psi) MPa [psi)

28-day Test DateS 28-day Test DateS 28-day Test DateS

C-P-Z4 45.7 46.8 86.7 77.9 86.3 92.1

[6630J [6780) [12,570) [11.290J [12,510J [13,360J

D-P-Z4 45.7 44.9 86.7 81.9 86.3 88.6

[6630J [651 OJ [12.570J [11,890J [12,150) [12,850)

E-P-Z4 32.4 29.2 72.7 78.8 79.8 97.3

[4700J [4230) [10,540J [11,430) [11,570] [14,110)

F-P-Z4 32.4 27.7 72.7 83.2 79.8 101.4i

[4700) [4020J [10,540J [12,060) [[11,570) [14,710)

A-P-Z2 31.1 34.0 62.6 68.3 75.7 87.4

[451 OJ [4930J [9,070J [9,910) [10,980) [12,670)

B-P-Z2 31.1 36.4 62.2 70.2 75.7 88.3

[4510) 5280J [9,070) [10,180J [10,980) [12,810)

a These cylinders and cubes were stripped at the same time as the test specimens and allowed tocure in the same environment as the test specimens. The cylinders were 102 mm x 203 mm (4 inx 8 in) and the cubes werel 51 mm x 51 mm (2 in x 2 in).

A major concern at the beginnin!g of this phase of the test was the load loss in the strands due to seatingof the chucks. This loss would be significant due to the short lengths of strand involved. As a result,several trial runs were made prior to post-tensioning the specimens to determine the amount of load lossand means to minimize this loss, As in the actual run, three strands were pulled at the same time in thetrial runs. The procedure used was as follows:

1. Pull all three strands so that the total load was equal to 0.8 Fpu'

2. Seat the chucks and rellease the load.3. Reload the strands to 0.8 Fpu and shim the chucks.4. Release the load.

10

IIIIIIIIIIIII,I

IIII

•

11

CHUCKS

BEARING PLATE

SHIM

AN:HORNlJT

PRESTFlESSINGSTRAND

SECTION A-A

o

JACK STAND - PLATEW8..DED TO BOX BEAM

534 kN (60-TON) CAPACITY

CENTER-HOLE JACK

PISTON

PLATE A

PLATE

A

A

o

25 mm (1 in)DYWIDAGBAR

Fig. 2.5 Jacking assembly for precast concrete Zone 4 specimens.

Five trial runs were made using 3 - 11 mm (0.44 in.) strands and one was made using 3 - 13 mm (0.5 in.)strands. The loads in the strands as obtained from the load cells indicated that the strands were evenlyloaded. The results from these runs are given in Table 2.4. The loads given in Table 2.4 for the load cellswere the sum of all three load cells. The individual load cell readings, 18 total, ranged from 0.58 ~u to0.77 Fpu with a mean of 0.69 Fpu and a standard deviation of 0.048 Fpu' On two of the runs, 4 and 6, theloads In the strands after 1 day (Run 4) and after 4 days (Run 6) showed a load drop of approximately1% when compared with the loads read immediately after Step 4.

The basic setup of the jacking assembly for the Zone 4 specimens is shown in Fig. 2.5. In the trial runs,three load cells (one per strand) were used to monitor the loads in the strands. The steel box beamshown in Fig. 2.5 was cut to the same length as the specimens. Another area of concern was that allthree strands be evenly loaded when pulled at the same time. Therefore, the hole in Plate A, as shownin Fig. 2.5, was chamfered so as to negate any misalignments of the jack. A 534 kN (60 ton) capacity,center-hole jack was used.

IIIIIIIIIIIIII,IIII

Table 2.4 Prestress Losses.

Step 18 Step 2 Step 3 Step 4Run

Jackb Load Celie Load Cell Jack Load Cell Load Cell

1 0.8 Fpu 0.713 Fpu 0.57 Fpu 0.8 Fpu 0.78 Fpu 0.66 Fpu

2 0.8 0,76 0.58 0.8 0.77 0.67

3 0.8 0,,77 0.59 0.8 0.78 0.70

4 0.8 0,,77 0.57 0.8 0.77 0.73

5 0.8 0,77 0.59 0.8 0.77 0.69

6d 0.8 0,76 0.59 0.8 0.76 0.69

a These step numbers refer to the post-tensioning trial run procedure described previously.b Jacking load as read from Cl calibrated pressure transducer.c Sum of the load from all thn:le strands as read from individual load cells.d Run in which 13 mm (0.5 in) strands were used.

The method used to post-tension the precast Zone 2 specimens was somewhat different from that usedfor the Zone 4 specimens. As shown in Fig. 2.2, two strands each top and bottom were used for the Zone2 specimens. It was decided th,at the simplest way to post-tension the specimens was to use two jacks(one jack per strand) and pUll both strands (top or bottom) simultaneously. Due to the limited spaceavailable at the end of the speciimen, one jack was set up at one end of the specimen and the other atthe opposite end as shown in Fi!g. 2.6. A 267 kN (30-ton), center-hole jack was used on each end of thespecimen.

12

IIIIIIIIIIIIIIIIII

•

CRANE(SUPPORTS wr.

OF JACK)

CRANE(SUPPORTS WT.

OF JACK)

13

Fig. 2.6 Set-up for post-tensioning precast concrete Zone 2 specimens.

When the test specimens were post-tensioned, only two load cells were used - one top and one bottom.The Zone 4 specimens were post-tensioned in eight stages and the Zone 2 in ten stages. These stageswere as follows:

Zone 4

1. Pull top strands to 0.4 Fpu'2. Seat chucks and release load.3. Pull bottom strands to 0.8 Fpu'4. Seat chucks and release load.5. Pull bottom strands to 0.8 Fpu'6. Shim chucks and release load.7. Pull top strands to 0.8 Fpu'8. Shim chucks and release load.

Zone 2

1. Pull bottom strands to 0.4 Fpu'2. Seat chucks and release load.3. Pull top strands to 0.8 Fpu'4. Seat chucks and release load.5. Pull bottom strands to 0.8 Fpu'6. Seat chucks and release load.7. Pull bottom strands to 0.8 Fpu8. Shim chucks and release load.9. Pull top chucks to 0.8 Fpu'10. Shim chucks and release load.

The loads in the two load cells after post-tensioning four of the specimens are given in Table 2.5 As seenin Table 2.5, the loads in the individual load cells were within one standard deviation of the mean asobtained in the trial runs.

IIIIIIIIIIIII'II

14

Boundary conditions for the test specimens were as follows: pinned at the column bottom and rollersupported at the column top and beam ends as shown in Fig. 2.7. The test set-up and test facility areshown in Fig. 2.8. Further details of the test facility may be found in Ref. 2.

The same type of instrumentation was used in the Phase II tests as was used for the Phase I tests. Thisincluded load cells on the ends of the beams, LVDTs for displacement measurements and strain gageson the beam reinforcement. The LVDTs were used to measure column displacements, openings betweenthe beam and column, and displacements at various locations on the beam. These beam displacementswere used to compute the strain along the beam. However, rotation of the beams made such straincalculations erroneous.

Table 2.5 Load Cell Readings After Post-Tensioning.

I

•

IIIIIIIIIIIIIIIII

0.65 Fpu

0.67 Fpu

0.67 Fpu

0.70 Fpu

Load Cell2b

0.65 Fpu

0.65 Fpu

0.71 Fpu

0.69 Fpu

Load Cell 18

E-P-Z4

F-P-Z4

A-P-Z2

B-P-Z2

Specimen

a Top set of strands.b Bottom set of stranljs.c 13 mm (0.5 in) Prestressing strands.

2.3 Instrumentation and Test Pmcedure

D

Fig. 2.7 Boundary conditions for the test specimens.

7777777777777777777777

Fig. 2.8 Test set-up and test facility.

15

UPPERCROSSHEAD

LOWERCROSSHEAD

IIIIIIIIIIIIII~

An axial load equal to 0.1 f~ Ag was applied to the column at the beginning of the test. The concretestrength was that obtained from the 28-day cylinder tests. The column was then laterally loaded at thecolumn top for the initial elastic cycle. This initial elastic cycle was designed to develop a load equal to75% of the calculated ultimate capacity of the monolithic beam. The top column displacements in theforward (south) and reverse (north) directions were measured. The yield displacement, t1y, was thendefined as the average of these two displacements divided by 0.75. The specimen was then cycled inincrements of t1y as described below.

The loading history for the precast Zone 4 specimens was two cycles each at + 2 .6v and + 4 .6v, threecycles each at + 6 ~ and + a, ~, two cycles at + 10 ~J and three cycles at + {2~. The roadingsequence for the precast Zone :2 specimens was two cycles at + 2 ~, three cycles at + 4 t1y, and twocycles at + 6 t1y. These 10adin!J histories matched those for the corresponding monolithic specimens.

Displacement ductility, J.L, is defined as the ratio of the maximum displacement achieved in any cycle tothe yield displacement. Ultimate displacement ductility, J.Lu' is defined as the ratio of the maximumdisplacement achieved for a slPecimen to the yield displacement. Failure was considered to haveoccurred when the lateral load dropped below 80% of the maximum load that was achieved in the firstcycle at 2 t1y.

16

IIIIIIIIIIIIIIIIII

•

I

-IIIIIIIIIIIIIII-

3.0 TEST OBSERVATIONS AND RESULTS

3.1 Precast Concrete Specimens C-P-Z4 and D-P-Z4

Specimens C-P-Z4 and D-P-Z4 were the precast Zone 4 specimens post-tensioned with two 25 mm (1 in.)post-tensioning bars and were detailed as shown in Fig. 2.1. The loading history for both specimens isshown in Fig. 3.1. The axial load on the column was 529 kN [119 kips] (0.1 f~ Ag, based on a 28-daystrength of 45.7 MPa [6628 psi]).

12

10

8

6

:::1. 4~::! 213::::l 0.75Q... -0.75zw

·2::liw(,)

S -40..

'"C -6

·8

-10

-12

Fig. 3.1 Loading sequence for specimens C-P-Z4 through F-P-Z4.

In the initial elastic cycle, no cracks were observed in either specimen. This was also the case for theprecast concrete specimens in Phase I. At 2 !!y. a few flexure and shear cracks were observed in thisseries of specimens. Very minor crushing of the beams was also noted at this ductility level. The crackbetween the beam and the construction joint was approximately 1 mm (0.04 in). Further cracking, shearand flexure, of both beams and columns was observed at 4~. The crack pattern is shown in Fig. 3.2.Some minor spalling and crushing of the beams occurred at thiS stage of the test. The opening betweenthe beam and construction joint as shown in Fig. 3.3 was approximately 4 mm (0.2 in). Additionalcracking of the specimens was observed at 6 !!y with the majority of the cracks occurring in the first cycleat 6!!y. The crack pattern in the joint region is shown in Fig. 3.4. Continued crushing of the beams andwidening of 'the opening between the beam and the construction joint were noted at this ductility level.The total opening between the beam and column was approximately 9 mm (0.4 in). Henceforth, the'beam-column opening' shall be defined as the sum of the opening between the beam and the grout jointand the grout joint and the column. The extent of crushing in the beam and the beam-column openingare shown in Figs. 3.5 and 3.6, respectively.

17

Fig. 3.:~ Crack pattern for specimen C-P-Z4 at 4 Ay.

Fig. 3.3 Opening between the beam and construction joint at 4 Ay.

18

IIIIIIIIIIIIIIIIII

•

IIIIIIIIIIIIIII

,Fig. 3.4 Crack pattern for C-P-Z4 at 6 fly.

Fig. 3.5 Crushing of the beam at 6 ~ - C-P-Z4.

19

.. ;u .. "

Fig. 3.6 Opening between the beam and column at 6 ~ - C-P-Z4.

No significant change in the crack pattern was observed at 8~. Some splitting cracks (cracking of thebeam top/bottom longitudinally) in the beams were noticed at this ductility level. At this point in the test,only additional beam crushing and widening of the beam-column opening were observed as depicted inFig. 3.7. The beam-column opening was approximately 16 mm (0.6 in). The crack widths in the columnjoint region and in the beams were still small. Crack propagations, continued crushing and spalling ofthe beams, and widening of the beam-column joint were noted at 1o~. The beam-column opening wasapproximately 20 mm (0.8 in) at 1a ~.

Both connections failed at 12 j~. Views of the overall connection and close-ups of the beams forspecimen C-P-Z4 are shown in Fig. 3.8, 3.9, and 3.10. Fig. 3.11 shows an overall view of specimen D-PZ4 at failure, JL = 12 dy' As seen in Fig. 3.9, extensive crushing and spalling of the beams occurred at12!:1y Also, as seen in Fig. 3.10, other than sustaining minor crushing and spalling, the grout jointperformed well throughout the tE!st. The beam-column opening at failure was approximately 25 mm (1.0in). Spalling of beams occurredl over an area which averaged 241 mm (9.5 in) from the column face.

20

IIIIIIIIIIIIIIIIIII I

-IIIIIIIIII

Fig. 3.7 Beam damage at 8 At -C-P-Z4.

Fig. 3.8 Specimen C-P-Z4 at failure - 12 lly.

2l

Fig., 3.9 Crushing of beams at 12~ - C-P-Z4.

Fig. 3.10 Opening between beam and column - C-P-Z4.

22

IIIIIIIIIIIIIIIIII

•

IIII·IIIIIIIIIIIIIII

Fig. 3.11 Specimen D-P-Z4 at failure - 12 !1y.

The load displacement plots for C-P-Z4 and D-P-Z4 are given in Figs. 3.12 and 3.13, respectively. Theload in the figures is the lateral load at the top of the column and the displacement is the displacementof the column top. As seen in the figures, the specimens exhibited stable behavior until failure andseverely pinched hysteresis curves. The experimental yield displacement was 5.3 mm (0.209 in) and 5.4mm (0.213 in) for specimens C-P-Z4 and D-P-Z4, respectively. As was mentioned earlier, the ultimatedisplacement ductility for both specimens was 12.

23

24

The experimental ultimate moments for C-P-Z4 were 169 kN-m (125 k-ft) and 171 kN-m (126 k-ft) at theface of the column. The first value was obtained in the first cycle at 6 Ay and the second in the first cycleat 4!:1y Similar values, 165 kN-m (1:~ k-ft) and 169 kN-m (125 k-ft) , were obtained for specimen D-P-Z4.Both of these values were obtained in the first cycle at 4 Ay.

A comparison of the energy absorbe!d by each specimen on a per cycle basis is shown in Fig. 3.14. Theenergy absorbed is defined as the area enclosed by the load displacement curve. As indicated by Figs.3.12 and 3.13 and as seen in Fi!~. 3.14, both specimens behaved in a very similar fashion. Thecumulative energy absorbed to failure by specimen C-P-Z4 was 93.9 k~-m (831 k-in) and by specimenD-P-Z4 was 92.9 kN-m (822 k-in).

IIIIIIIIIIIIIIIIII

•

101.661.020.3-20.3

Displacement (mm)

Fig. 3.13 Hysteresis curves forD-P-Z4.

333.6

200.2

-333.6

-101.6 -61.0101.6101.020.3-20.3

Displacement (mm)

Fig. 3.12 Hysteresis curves forC-P-Z4.

333.6

200.2

-333.6

-101.6 -61:0

66.7 66.7

Z Z6 6"0 "0ltl -66.7 ltl -66.70 0..J ..J

-200.2 -200.2

1 kN-m =8.85 k-in

20

16

o

• C-P-Z4

III D-P·Z4

IIIIIIII

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

CYCLE NUMBER

Fig. 3.14 Energy absorbed per cycle by specimens C-P-Z4 and D-P-Z4.

The maximum strains in the reinforcing bars are shown in Figs. 3.15 through 3.30. In these figures, theterm "11 S" refer to the first cycle at jJ. = 0.75 :7l on the excursion to the south, "41 S" refer to the firstcycle at jJ. =4~ on the excursion south, "122 N refer to the second cycle at jJ. = 12 Ay on the excursionnorth, and so forth. Recall that the precast concrete beams have four #3 reinforcing bars located in thecorners of the ties. In the following and subsequent figures which show the extent of reinforcing baryielding, the term 'northeast· refers to a reinforcing bar located on the east side of the north beam,"southwest" refers to a reinforcing bar located on the west side of the south beam, etc. Also, 'OP" refersto the top of the beam. The average extent of reinforcing bar yielding was 393 mm (15 in) for C-P-Z4 and337 mm (13 in) for D-P-Z4. These average values were determined from Figs. 3.15 through 3.30. Theyield length for each bar was defined as the length at which the strain in the reinforcing bar was greaterthan or equal to the yield strain. However, as observed during the tests and from Figs. 3.15 through 3.30,the yielding in the beam reinforcement was not extensive. Also from Figs. 3.15 through 3.30, it can beseen that the highest strains recorded in the reinforcement occurred at jJ. = 4~. In the following cycles,the strains in the beam reinforcement decreased indicating that debonding of the post-tensioning barsoccurred at this stage and that the main load resistance to the applied loads was provided by the posttensioning bars.

Three ties in the beams were instrumented with strain gages. Of the three, only the first tie, located 42mm (1.7 in) away from the column face, yielded. The other two ties were located 110 mm (4.3 in) and245 mm (9.7 in) away from the column face. The highest recorded strains in these ties wereapproximately half of the yield strain or less.

25

IIIIIII

~ 115

• 11 N

~ 415

• 41 N

iii 815

iii 81 N

---<r-- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

500400300200100

-3000 -+---.-....,....~"r--.L.,--...--r-...---r-......"""T-....--'T--,

o

3000

2000

1000

c:.~

t:i 00lJ:ij

·1000

·2000

Distance Away From Column Face (mm) IFig. 3.1 S Top northeast reinforcing bar strains - C-P-Z4.

Fig. 3.16 Bottom northeast reinforcing bar strains - C-P-Z4.

IIIIIIIII

~ 11 S

• 11 N

~ 41 S

• 41 N

iii 81 S

Ii 81 N

---<r-- 122 S

• 122 N

----- YIELD--_ ... - -YIELD

600500400300200

26

Di!ltance Away From Column Face (mm)

YIELD

100

e--z:::::::::==~~

~~

----~-----------------y~~----

·3000 +----T--r--,--r----r---r----r---r--...---r-.....--"""T--o

o

3000

2000

1000

c:"ill.l:I 0'"g:ij

·1000

·2000

I

•

3000

2000

1000

c.~

en 0g~

-1000

-2000

~ 11 S

YIELD • 11 N

~ 41 S

• 41 N

A 81 S.. 81 N

--0-- 122 S

• 122 N

----- YIELD----- -YIELD

YIELD

600500400300200100-3000 -+.--...-....--4--....-.......-,.-.......-,--........-,--........--,r--.

o

Distance Away From Column Face (mm)

Fig. 3.17 Top northwest reinforcing bar strains - C-P-Z4.

Fig. 3.18 Bottom northwest reinforcing bar strains - C-P-Z4.

~ 11 S

• 11 N

~ 41 S

• 41 N

A 81 S.. 81 N

--0-- 122 S

• 122 N


600

YIELD

500400300200100


27

o

1000

3000

2000

-1000

-3000 +-..........-"T"""-...-"T"""-...-~ .......-~.......-~.......-r-....,o

·2000

IIIIIIIII.I

I3000 I

0 115YIELD • 11 N

2000~ 415 I• 41 N.. 815

1000,/ I.. 81 N

c::

~~:: :====: -0- 1225~ • 122 Nt; 0g

~~----- YIELD I:E ----- -YIELD

-1000

I-2000 -----,-------------------------YIELD

-3000 I0 100 200 300 400 500 600

IDiSlance Away From Column Face (mm) IFig. 3.19 Top southeast reinforcing bar strains· C-P-Z4. I

3000 I~ 115YIELD • 11 N

2000~ 415 .1• 41 N

1000.. 815.. 81 N

Ic:: --0-- 122 S'(ij

tl 0 • 122 N§ ----- YIELD:E ----- -YIELD I-1000

-2000YIELD I

-3000 I0 100 200 300 400 500 600

Dislance Away From Column Face (mm) IFig. 3.20 8;onom southeast reinforcing bar strains - C·P-Z4.

I28

I

•

3000

~ 11 SYIELD • 11 N

2000~ 41 S

• 41 N

1000.. 81 S.. 81 N

c:t~

-0-- 122 Sg ..- • • 122 N'" 0 0g 0 0 ----- YIELD~

~----- -YIELD

·1000

·2000YIELD

600500400300200100·3000 +-.....,.--r---..---r---..--r----y-........-y-........-,r-.....

o


Fig. 3.21 Top southwest reinforcing bar strains - C-P-Z4.

YIELD

·1000

-2000

3000

~ 11 S

YIELD • 11 N2000

~ 41 S

• 41 N

1000A 81 S.. 81 N

c: -0-- 122 S'iii~ 0 • 122 Ng ----- YIELD~ ----- -YIELDI

I

III

600500400300200100


-3000 +----.-"'T"""---........"""T'"-.....-"""T'"-.....--r-......--r..........-'"""'T----.oI

IIII

Fig. 3.22 Bottom southwest reinforcing bar strains - C-P-Z4.

29

I3000 I

0 11 S

YIELD • 11 N2000 I~ 41 S

• 41 N

A 81 S1000

I• 81 N

--0-- 122 Sc:,E • 122 Nin 00 ----- YIELD I0~ ----- -YIELD

·1000

·2000 -------------------~-~-I

YIELD

·3000 I0 100 200 300 400 500 600

Distance Away From Column Face (mm) IFig. 3.2:3 Top northeast reinforcing bar strain - D-P-Z4. I

3000 I~ 11 S

• 11 N2000

~ 41 S I• 41 N

6 81 S1000

• 81 N

Ic: --0-- 122 Siiiix 0 • 122 N§ ----- YIELD~ ----- -YIELD I·1000

·2000 ---------------------- IYIELD

·3000 I0 100 200 300 400 500 600

Distance Away From Column Face (mm) IFig. 3.24 Elottom northeast reinforcing bar strains - D-P-Z4.

I30

I

•

e- 115

• 11 N

~ 415

• 41 N,. 815,. 81 N

-0- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

500400300200


100-3000 +---'-~""''''''''''"''T'"-''-'"''T'"-'-""''T"'-.---,-- ......~-...

o

3000

2000

1000

c:'iiiiil 000~

-1000

-2000IIII Fig. 3.25 Top northwest reinforcing bar strains - D-P-Z4.

31

Distance Away ~rom Column Face (mm)

Fig. 3.26 Bottom northwest reinforcing bar strains - D-P-Z4.

600500400300200100-3000 +---.--,---..----r--..-"""T"'-.-"""T"'-.---,--......~--.

o

IIIIIIIIII

I


IIII

II

I600

YIELD

500400300200100

-2000

-1000

·3000 +---r-"T"""-...-"T"""........-~--.--r--.--r--.--r-....,o

3000

e- 11 S

• 11 N2000

~ 41 S

• 41 N.. 81 S1000 .. 81 N

l: --0-- 122S.~ ..- • 122 N'l;; 0§ 0""- ----- YIELD:E ----- -YIELD

Fig. 3.27 Top southeast reinforcing bar strains - D-P-Z4. II

II

II.--

----/-' ---- -- -- -- ----- -- ------YIELD

-1000

·2000

3000

0 11 S

YIELD • 11 N2000 ---------

~ 415

• 41 N

1000.. 815.. 81 N

l: -<>-- 1225iii.= • 122 N<II 0g ----- YIELD:E ----- -YIELD

I600500400300200100

·3000 +---.-,...--,._..,--....-..,--....--r-..---r-...--y--..o

Disltance Away From Column Face (mm) IFig. 3.28 Bottom southeast reinforcing bar strains - D-P-Z4.

32II

I

• 3000~ 11 S

I YIELD • 11 N2000

~ 41 S

• 41 N.. 81 S

I 1000 .. 81 N

c: -<>- 122S.~

• 122 N

I1ii 00 ----- YIELDt5:E ----- -YIELD

·1000

I·2000 ------------------------------

YIELD

I -30000 100 200 300 400 500 600

I Distance Away From Column Face (mm)

I Fig. 3.29 Top southwest reinforcing bar strains - D-P-Z4.

I 3000~ 11 S

• 11 N

I 2000~ 41 S

• 41 N.. 81 S

I1000 .. 81 N

c: -<>- 122 S"iil,\:> 0 • 122 NII>

Ig ----. YIELD:E ----- -YIELD

·1000

I ·2000 ------------------------------YIELD

I ·30000 100 200 300 400 500 600


I Fig. 3.30 Bottom southwest reinforcing bar strains - D-P-Z4.

33

II

3.2 Precast Concrete Specimens E-P-Z4 and F-P-Z4

Specimens E-P-Z4 and F-P-Z4 a.re the Zone 4 precast ,concrete specimens which were post-tensionedusing 6 - 11 mm (0.44 in) prestressing strands as shown in Fig. 2.1. The loading histories for specimensE-P-Z4 and F-P-Z4 were identicall to those for the previous precast concrete specimens as shown in Fig.3.1. The applied axial load was 376 kN [84.5 kips] (0.1 f~ Ag based on a 28-day strength of 32.4 MPa[4698 psi]).

In the initial elastic cycle, no cracks were noted in either specimen as was the case for the previous fourprecast concrete specimens. At 2 !:..y. a few flexure and shear cracks were observed in the beams andin the column. Very minor crushing In the beams was noted in F-P-Z4 at 2~. The shear cracks in thecolumn of F-P-Z4, Fig. 3.31, differed slightly from those in specimen E-P-Z4 in that the cracks in F-P-Z4started out as flexure cracks, then became shear cracks and were slightly shallower than those inspecimen E-P-Z4. The shear cracks in specimen E-P-Z4 are shown in Fig. 3.32. This slight variation inthe shear cracks could a result of one of th.e duets in specimen F-P-Z4 not being completely grouted.More cracking and crack propagation occurred at 4 Ay. Additional beam crushing also occurred at thisstage. The opening between thB beam and column was approximately 5 mm (0.2 in) as shown in Fig.3.33. The extent of beam crushing is shown in Fig. 3.34.

._ i" -(

, i'"

'''.,,\ '\ \"

, \,-

Fi!J.3.31 Shear cracks in F-P-Z4 at 4 Ay.

34

IIIIIIIIIIIIIIIIII~

IIIIIIIIIIIIIIIIII.'

Fig. 3.32 Shear cracks in E-P-Z4 at 4 !:..y.

, ,__....__....L,.,,~"'",::f.,('J,... ,-',

Fig. 3.33 Opening between beam and column at 4 !:..y. F-P-Z4.

35

Fig. 3.34 Crushing of beam at 4l!.y, F-P-Z4.

Minor cracking and crack extensions were noted at both 6 !:.y and 8l!.y. Continued beam crushing andspalling also occurred at these ductility levels. The opening between the beam and column wasapproximately 11.5 mm (0.45 in) ,at 6~ and 15.5 mm (0.61 in) at 8l!.y. The crack pattern, beam openingand crushing for specimen F-P-;~4 at B l!.y are shown in Fig. 3.35. No significant change in the crackpattern occurred at the next two ductility levels, 10 fly and 12~. Further widening of the openingbetween the beam and the column and crushing of the beams tooK place at these ductility levels. Theopenings between the beam and column were approximately 21.5 mm (0.85 in) at 10 l!.y and 27 mm (1.06in) at 12 !:'y' Fig. 3.36 shows the! opening in which the strands are visible at 12 !:.y and Fig. 3.37 showsan overall view of the connection at 12~. Fig. 3.38 shows specimen E-P-Z4 at 12~. The average extentof the spalling was approximatoly 200' mm (8.11 in) for specimen E-P-Z4 and 248 mm (9.76 in) forspecimen F-P-Z4. Both specimens failed at 12~. The cracks in the column joint region were still fineat failure and the fiber reinforcedl construction joints held together very well throughout the test.

36

IIIIIIIIIIIIIIIIII

•

IIIIIIIIIII

Fig. 3.35 Connection F-P-Z4 at 8 t.y.

,.\. --

'.

Fig. 3.36 Opening between the beam and column at 12 ~, F-P-Z4.

37

Fig. 3.37 Specimen F-P-Z4 at failure - 12 Ay.

';\u.,,,;:'-- ~--=< -~' -i.'- i

\

Fig. :3.38 Specimen E-P-Z4 at failure - 12 ~.

38

IIIIIIIIIIIIIIIII

The hysteresis curves for E-P-Z4 and F-P-Z4 are shown in Figs. 3.39 and 3.40. Again, both specimensbehaved very similarly and exhibited severly pinched hysteresis curves. The yield displacement was5.7 mm (0.225 in) for specimen E-P-Z4 and 5.5 mm (0.218 in) for specimen F-P-Z4. The ultimatedisplacement ductility for both specimens was 12.

39

The maximum strains in the reinforcing bars are giJen in Figs. 3.42 through 3.57. The average extent ofreinforcing bars yielding was 95 mm (3.7 in) for E-P-Z4 and 148 mm (5.8 in) for F-P-Z4. Again. as withthe previous precast specimens, the highest recorded strains occurred at 4 c!'y and decreased thereafter.Only the first tie (42.3 mm [1.7 in] from the column face) in the beams yielded. Two other ties, located110 mm (4.3 in) and 245 mm (9.7 in) from the column face, registered strains of the order of half the yieldstrain or less.

101.661.020.3-20.3

Displacement (mm)

Fig. 3.40 Hysteresis curves forF-P-Z4.

333.6

200.2

-333.6

-101.6 -61.0101.661.020.3-20.3

Displacement (mm)

The experimental ultimate beam moments at the column face were 146 kN-m (108 k-ft) and 137 kN-m(101 k-ft) for E-P-Z4 and 139 kN-m (102 k-ft) and 135 kN-m (100 k-ft) for F-P-Z4. The values for E-P-Z4were obtained in the first cycle at 8 ti.y and those for F-P-Z4 were obtained in the first cycle at 4 c!'y.

A comparison of the per cycle energy absorbed for the two specimens is given in Fig. 3.41. Thecumulative energy absorbed to failure was 110.76 kN·m (980 k-in) for E-P-Z4 and 109.39 kN-m (968 k-in)for F-P-Z4.

Fig. 3.39 Hysteresis curves forE-P-Z4.

333.6

200.2

-333.6

-101.6 -61.0

66.7 66.7Z Z:=. :=."0 "0ell -66.7 ell -66.70 0

...J ...J

-200.2 -200.2

IIIIIIIIIII

1 kN-m = 8.85 k-in20

• E·P-Z4m F·P·Z4

16

'E 12Ze>-C)a::w 8Zw

4

o2 :I 4 5 6 7 8 9 10 11 12 13 14 15 16

CYCLE NUMBER

Fig. 3.41 E:nergy absorbed by specimens E-P-Z4 and F-P-Z4.

III'IIII


40

Fig. 3.42 Top northeast reinforcing bar strains - E-P-Z4.

IIIIIIIII

600

YIELD

500400300200100

-2000

·3000 +-_,.--r--...--y---.r---y--r---r--_-,--...---r-...

o

3000

~ 11 S

YIELD • 11 N2000 -----,-------------------------

~ 41 S

~• 41 N

1000 • 81 S.. 81 N

c: --0-- 122 SCil

~ill 0 • 122 N0 t=3;: : ;at3 ----- YIELD:E ----- -YIELD

-1000

••

3000

Fig. 3.43 Bottom northeast reinforcing bar strains - E-P-Z4.

0 115

• 11 N

~ 415

• 41 N.. 815.. 81 N

--0-- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

500400300200100

YIELD


2000

.3000 +----.-...,.-.......,,..........,..-...--....,..-..._-r--.....-.......-.,...........---.o

·2000

1000

c:"~

u; 00tl~

-1000

II

II

I

~ 115

• 11 N

~ 415

• 41 N.. 815.. 81N

--0-- 122 S

• 122 N

----- YIELD

----- -YIELD

600

YIELD

500400300200100


2000

3000

-2000

-3000 +---T--r-.......--r-.......-,.-........-.,............-.,............-,---.

o

1000

c:"16.l:o 0III

§~

·1000

II

I'IIII

III

Fig. 3.44 Top northwest reinforcing bar strains - E-P-Z4.

41

I

3000 IYIELD

2000

1000

o

-1000

0 115

• 11 N

~ 415

• 41 N.. 815.. 81 N

---0-- 1225

• 122 N

----- YIELD

----- -YIELD

III'I

Fig. 3.45 Bottom northwest reinforcing bar strains - E-P-Z4.

III

600

YIELD

500400300200100


-3000 +---.--r-........,...--r--....-""'T"---r-.,.....-'T-...,....~-..o

·2000

'II

III

0,...-- 115

• 11 N

~ 415

• 41 N.. 815.. 81 N

---0-- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

500400300200100


o

YIELD

1000

3000

2000

-2000

·1000

·3000 +-.........-,.....-..-,........,.-T"""'"--.---r------r-----r--.o

Fig. 3.46 Top southeast reinforcing bar strains - E-P·Z4. I42

I

~ 115

• 11 N

~ 415

• 41 N

'" 815.. 81 N

--0-- 1225

• 122 N


600

YIELD

500400300200100

1000

o

3000

2000

-2000

-1000

-3000 +-~-""--"'-""--"'-""",--'--,,-""""-,,-""""-r--""

o

II


Fig. 3.47 Bottom 50utheast reinforcing bar strains - E-P-Z4.

600

YIELD

500400300200100


·1000

-2000

·3000 +---.-....--..-...,...-.--...,...-r--........-r----.--............,........,o

3000

~ 115YIELD • 11 N

2000 -----------------~ 415

• 41 N

1000.. 815.. 81 N

c: --0-- 1225"16.= • 122 NrJl 0§ ----. YIELD~ ----- -YIELDI,

I'II

III

III

Fig. 3.48 Top southwest reinforcing bar strains - E-P-Z4.

43

II

II

~ 11 S

• 11 N

~ 41 S

• 41 N

a 81 S

iii 81 N

--0- 122S

• 122 N


600

YIELD

500400300200100

2000

o

3000

1000

-1000

-3000 +---r-................~.......-...-.......- __~-__.....,..-.....-~--.

o

-2000


Fig. 3.49 Elottom southwest reinforcing bar strains - E-P-Z4.

IIII

I'II

600

YIELD

500400300200100


-1000

-3000 +---r--T--..,-.......- __.......- __~-__.....,..-..--~--.

o

-2000

3000

~ ~ 11 S

----~ YIELD • 11 N2000 -'------------'- _.- -- -- - - --

~ 41 S

• 41 N

1000 \ • 81 S.. 81 Nc: --0- 122 S

"iiit: 0 • 122 Ng ----- YIELD::ij ----- -YIELD

Fig. 3.50 Top northeast reinforcing bar strains· F-P-Z4.

44

I

~ 115

• 11 N

~ 415

• 41 N

* 815

* 81 N

----0-- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

YIELD

500400300200


100-3000 +---.-..,...--.,......-r--r__-r--r__--r-or__--r-......--"T---.

o

·1000

·2000

3000

2000

1000

c:1!!1ii 00b~

II

III

II

I Fig. 3.51 Bottom northeast reinforcing bar strains· F-P-Z4.

2000

3000


I

~ 115

• 11 N

~ 415

• 41 N

* 815

* 81 N

----0-- 1225

• 122 N

----. YIELD

----- -YIELD

800

YIELD

YIELD

600400200

1000

c:"iij

~ 0g~

·1000

·2000

-30000

I·

I

II

II

I

I Fig. 3.52 Top northwest reinforcing bar strains - F-P-Z4.

I45

I

I3000

II

II

~ 11 S

• 11 N

~ 41 S

• 41 N

iii 81 S

iii 81 N

--0-- 122S

• 122 N


600500400

YIELD

300200100

2000

-3000 4---r-.,..L-....,,.--r--....,,.-~"""T'"-r-........-r-........---.,r--....o

1000

c:oil!iii 00b

:iE:

-1000

·2000

Di!ltance Away From Column Face (mm) IFig. 3.53 lBottom northwest reinforcing bar strains - F-P-Z4. I

3000

2000

1000

c:iii~ 00b

:iE

-1000

-2000

-30000 ~~oo 400

YIELD

YIELD·

600 800

~ 11 S

• 11 N

~ 41 S

• 41 N

iii 81 S

iii 81 N

--0-- 122S

• 122 N

----- YIELD

----- -YIELD

IIIIII

Di!:tance Away From Column Face (mm) IFig. 3.54 Top southeast reinforcing bar strains - F-P-Z4.

46 II

I

~ 115

• 11 N

~ 415

• 41 N.. 815.. 81 N

--0-- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

YIELD

500400300200


100

-1000

-2000

-3000 +---.-...,.....--.-...,...-..-...,...-..-""'T'"-__"""'T'-or-.......----.

o

3000

2000

1000

c"!!!<ii 00l:5:ij

I

II

II

II

Fig. 3.55 Bottom southeast reinforcing bar strains - F-P-Z4.

~ 115

• 11 N

~ 415

• 41 N.. 815.. 81 N

--0-- 1225

• 122 N

----- YIELD

----- -YIELD

600

YIELD

YIELD

500400300200


100

·2000

·3000 +---.--r---'-""T'"--..-"-T--"-"""T'"-..--r-..---r--.o

3000

2000

1000

c"iij

~ 0§5j

-1000

I

IIIIII

II

Fig. 3.56 Top southwest reinforcing bar strains - F-P-Z4.

47

I


48

Fig. 3.57 Elottom southwest reinforcing bar strains - F-P-Z4.

IIIIIIIIIIIIIIIII~

II

600

YIELD

500400300200100-3000 -t---..-T""'--.--"T'---.--.,----.--r--r--r--r--r--....,

o

-2000

3000~ 115

YIELD • 11 N2000 -----------------------

~ 41 S

• 41 N

10006 81 S

• 81 NC"

---0-- 1225c:-.~

i= • 122 N'lii 00h ----- YIELD~ ----- -YIELD

-1000

3.3 Precast Concrete Specimens A-P-Z2 and B-P-Z2

Specimens A-P·Z2 and B-P-Z2 WElre the precast concrete Zone 2 specimens and were detailed as shownin Fig. 2.2. The loading history is shown in Fig. 3.58. The column axial load was 173.9 kN (39.1 k)[0.1 f~ Ag based on a 28-day strElngth of 31.1 MPa (4510 psij].

IIIIIIII'IIIIIIII,I'II

6

4~

~ 2:Ji=0 0.75:J0I-z -0.75UJ::!:UJ0 -2:5a.(J)

is -4

-6

Fig. 3.58 Loading sequence for specimens A-P-Z2 and B-P-Z2.

In the initial elastic cycle, a few short, hairline flexure cracks were noted in the column in specimen A-P-Z2.No cracks were observed in specimen B-P-Z2. However, very minor crushing of the construction jointswas noted on the tension side of both beams of specimen B-P-Z2. No obvious explanation was foundfor this deviation. At 2 ~I flexure cracks were observed in the beams and flexure and shear cracks wereobserved in the column joint region. Minor crushing of the beams also occurred at this stage. The extentof cracking at 2 f:1y is shown in Fig. 3.59. More shear cracks in columns and beams developed at 4 f:1y.In addition, extensive crushing of the beams occurred at 4 f:1y. The opening between the beam andcolumn was approximately 5 mm (0.2 in). The column joint region was in good condition at this stagewith the column crack widths still narrow. The average length of spall in the beams for both specimenswas approximately 175 mm (6.9 in). Figs. 3.60 through 3.62 show the crack pattern, crushing and beamopening at 4 f:1y, respectively. Both specimens were considered to have failed at this stage. Fig. 3.63shows the joint region of specimen B-P-Z2 at failure. .

49

Fig. 3.59 Crack pattern at 2 !1y . A-P-Z2.

50

IIIIIIIII'IIIIIIIII~

Fig. 3.60 Joint region at failure, 4 ~ - A-P-Z2.

•'I

"III•

Fig. 3.61 Beam crushing at 4 ~ - A-P-Z2.

51

Fig. 3.62 Opening between beam and column at 4 Ay - A-P-Z2.

Fig. 3.63 Joint region at failure, 4 Ay - B-P-Z2.

52

'IIIII

I

IIIIII

The hysteresis curves for specimens A-P-Z2 and 8-P-Z2 are shown in Figs. 3.64 and 3.65, respectively.The yield displacements were 8.5 mm (0.333 in) and 8.4 mm (0.330 in) for specimens A-P-Z2 and 8-P-Z2,respectively. The ultimate displacement ductility was 4 for both specimens.

66.7 66.7

Z Z~ ~

"C "CCfl -66.7 Cfl -66.70 0

...J ...J

-200.2 -200.2

101.661.020.3-20.3

333.6

200.2

-333.6

·101.6 -61.0101.661.020.3-20.3

333.6

200.2

-333.6

-101.6 -61.0

Displacement (mm) Displacement (mm)

II

Fig. 3.64 Hysteresis curves forA-P·Z2.

Fig. 3.65 Hysteresis curves for8-P-Z2.

I'IIIIII

The experimental ultimate moments were 52 kN-m (38 k-ft) and 54 kN-m (40 k·ft) for A-P-Z2 and 51 kN-m(37 k-ft) and 54 kN-m (40 k-ft) for 8-P-Z2. Three of these values were obtained in the first cycle at 2 ~y

and the fourth (54 kN-m [40 k-ft] for 8-P-Z2) in the first cycle at 4 ~Y'

A comparison of the energy absorbed on a per cycle basis is given in Fig. 3.66. The cumulative energyabsorbed to failure for specimen A-P-Z2 was 7.4 kN-m (65.2 k-in) and for specimen 8-P-Z2 was 8.8 kN·m(78.1 k·in).

53

•

16

1 kN-m = 8.85 k-in20 I

IIIIIIIIIIIIIIII

87654

CYCLE NUMBER

320-+--'"

• A-P-Z211 B-P-Z2

54

Fig. 3.66 E:nergy absorbed by specimens A-P-Z2 and S-P-Z2.

E 12Ze.>-Cla:w 8Zw

4

The reinforcing bar strains are shown in Figs. 3.67 through 3.82. The average length over which thereinforcing bars yielded was 1110 mm (4.3 in) and 112 mm (4.4 in) for specimens A-P-Z2 and S-P-Z2,respectively. The maximum vallJes were obtained at 4 Ct..y•. The first two ties located 42 mm [1.7 in) and110 mm (4.3 in) from the column face in the beams yieldea. A third tie located 245 mm (9.7 in) registeredlow strains throughout the test.

•

3000

YIELD2000 ------------------------------

-0-- 11 S

~--.- 11 N

1000 --0-- 21 S

----- 21 Nc ---6-- 41 S'm...t'i 0 ---6-- 41 N0 ;;;: : Ih YIELD~

-YIELD-1000

3000

.Dis1ance Away From Column Face (mm)

Fig. 3.67 Top northeast reinforcing bar strains· A-P-Z2.

600

-YIELD

500400300200100·3000 +---r-...,..---.--r----,..---r--..---r--r----r-...---,.---.

o

-2000

II

II

YIELDIII

2000

1000

o

-0-- 11 S--.- 11 N

--0-- 21 S--- 21 N

---6-- 41 S

---r- 41 N

YIELD

·YIELD-1000

DiS1ance Away From Column Face (mm)

·2000 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --YIELD

600500400300200100·3000 +---r-'T""".......-'T""".......-~-.--1'-........-,._........~.--....

oII

I

I Fig. 3.68 Bottom northeast reinforcing bar strains· A-P-Z2.

II

55

I3000 I2000

1000

c:: 0-"iii.=- . 0Ulg ..:E .. ,

YIELD

---0-- 11 S

--+-- 11 N

--0-- 21 S

----- 21 N

-....- 41 S

-....- 41 N

YIELD

-YIELD

III

-1000

III

600

-YIELD

500400300200100


-3000 +--,.--r-'--.--r---....--r--...--r-----r-....---r--.o

-2000

I

I

II

III

600

-YIELD

500400300200100

Fig. 3.69 Top northwest reinforcing bar strains - A-P-Z2.


-3000 +---...-.,.......-....-.,.......-..---r-........-......--.--......--.---,r--...,o

-2000

3000

YIELD2000 -----_._--~---------------

~ 11 S

~--+-- 11 N

1000 --0- 21 S

----- 21 Nc:::

I --r- 41 S'iij,\::0 0 -....- 41NUlg 0-- ; ; 0 ~ YIELD:E t= iii

-YIELD-1000

Fig. 3.70 Bottom northwest reinforcing bars strains - A-P-Z2. I56

II

II

3000

I YIELD2000

I 1000 --0- 11 S---.- 11 N

c: ---0-- 21 S

I.~

21 N'in 0 ----0 ----.-- 41 S0~ ----.-- 41 N

I·1000 YIELD

-YIELD

·2000 -------------------------I

-YIELD

·3000

I0 100 200 300 400 500 600


:1Fig. 3.71 Top southeast reinforcing bar strains - A-P-Z2.

I 3000

IYIELD

2000 ---------------------0- 11 S

---.- 11 N

I 1000 ---0-- 21 S---- 21 N

c: ----.-- 41 S(ij

I~ 0 ----.-- 41 N§ YIELD~ -YIELD

·1000

I·2000 -------------------------

-YIELD

I ·30000 100 200 300 400 500 600


I Fig. 3.72 Bottom southeast reinforcing bar strains - A-P-Z2.

I57

I

I

II

II

I

II

~ 11 S

---+- 11 N

--0-- 21 S

------ 21 N

---+- 41 S. ---+- 41 N

YIELD

·YIELD

600500400300200


-YIELD

100·3000 +--.---r--........-r---.--~---,.---r- ........---,r---.---,

o

·2000

3000

2000

1000 ...c ..

"iiiiii 000 ~

~ Do

-1000

Fig. 3.73 Top southwest reinforcing bar strains - A-P-Z2.

3000

2000

1000

c"iii~ 0'"g~

·1000

____ ~. Y~E':D__ •

6"

--0- 11 S

---+- 11 N

--0-- 21S--- 21 N

---+- 41 S

---+- 41 N

YIELD

-YIELD

IIIII

·2000 II

600500400300200

-YIELD

100-3000 +----.-......-.....--r-......-......,--.--.--.---r----.--,

o

Distance Away From Column Face (mm) IFig. 3.74 Elottom southwest reinforcing bars strains - A-P-Z2.

58II~

-I

3000

2000

1000

o

-1000

YIELD

--0-- 11 S

-....- 11 N

--0-- 21 S---- 21 N

-...- 41 S

-...- 41 N

YIELD

-YIELD

II'II

-2000 - - - - -- -- -- -- -- -- - - -- -- -:YiaD

·3000 .!---.--..-----r-..,......,...--.-~--.--r-----6TOO~o 100 200 300 400 500


Fig. 3.75 Top northeast reinforcing bar strains. B-P-Z2.

3000

IIIIII

YIELD2000

1000

o

-1000

~ooo -----------------------:Yia~----

-3000 +---.--r------,.-..,......,...--.-~--.--r__--~~o 100 200 300 400 500 600


--0-- 11 S

-....- 11 N

--a-- 21 S

-.- 21 N

-...- 41 S

-...- 41 N

YIELD

-YIELD

III

Fig. 3.76 Bottom northeast reinforcing bar strains. B-P-Z2.

59

I

YIELD

3000

2000

1000

c;.

~u; 00 ..-tl~ ----1000

·2000-YIELD

---0-- 11 S- 11 N

---0- 21 S

----- 21 N

--.- 41S

--.- 41 N

YIELD

-YIELD

IIIIII

600500400300200100-3000 +----r-"T"""-...-"T"""--.--T"'""........-.---.--.---.--r--...,

o

Distance Away From Column Face (mm) IFig. 3.77 Top northwest reinforcing bars strains· B-P-Z2. I

3000 IYIELD

;::;;--;:::+

2000

1000

o

·1000

~/-- tee •

i

---0-- 11 S

--..... 11 N

~ 21 S---- 21 N

----.- 41 S

--.- 41 N

YIELD

-YIELD

III

·2000-YIELD I

I600500400300200100·3000 +---....,......-r--"...-...,..-...--...,..-...--~- .......~-..,....~----.

o

Di!ltance Away From Column Face (mm) IFig. 3.78 Bottom northwest reinforcing bar'strains - B-P-Z2.

60II

3000

2000

1000

c1.i!'In 00~

~

·1000

YIELD

~ 11 S--+- 11 N

~ 21 S

---- 21 N

--...- 41 S--...- 41 N

YIELD

-YIELD

-2000-YIELD


600500400300200100-3000 +--"'-T'"""--'--T'"""--'--~"""-r--r--r--r---,r---'

o

I

Distance Away From Column Face (mm),

Fig. 3.79 Top southeast reinforcing bar strains - B-P-Z2.

~ooo -------------------------------YIELD

600500400300200100-3000 +---r--r-.......--r---r---r-..-....,..-.......~----.

o

3000

YIELD2000 ------------------------------

~~ 11 S-....- 11 N

1000 --a-- 21 S

---- 21 Nc

~ 41 S"1ij -..-ii; 0 -..- 41 N0

~0;~ YIELD

~·YIELD

-1000

II

II

IIIII Fig. 3.80 Bottom southeast reinforcing bar strains - B-P-Z2.

II

61

3000 •YIELD

I2000 -----------------------0-- 11 S-- 11 N

1000 ---0-- 21 S

I-...- 21 Nc --r- 41 S

~ 0 --.-- 41 N0

I!J YIELD:iE"

-YIELD·1000

·2000 ------------------------------- I-YIELD

·3000 I0 100 200 300 400 500 600

Distance Away From Column Face (mm) IFig. 3.81 Top southwest reinforcing bar strains - B-P-Z2. I

3000 IYIELD

2000 -----,---------_._-------------- I--0-- 11 S-- 11 N

1000 --0-- 21 S

---- 21 N Ic -....- 41 Somi;i 0 --.-- 41 Ng YIELD I:iE

-YIELD·1000

."

I-2000 ------,-------------------------YIELD

-3000 I0 100 200 300 400 500 600

Distance Away From Column Face (mm) IFig. 3.82 Bottom southwest reinforcing bar strains - B-P-Z2. I

62

II

•IIIIIIIIIIIIIII

4.0 DISCUSSION OF TEST RESULTS

4.1 Displacement Ductility

The ultimate displacement ductilities for all the specimens (Phase I and Phase II) are given in Table 4.1.Also shown in Table 4.1 are the connection stiffnesses and story drifts at failure. Story drift is defined asthe ratio of the story displacement to the story height.

Table 4.1 Yield Displacement and Displacement Ductility.

Init. Elast. Ult.

Specimen f' a Exp. Yield J.Lu Connection StorycStiffnessb Drift

MPa (psQ mm (in.) kN/mm (klin) (%)

A-M-Z2 43.5 6310) 9.12 (0.359) 6c 7.7 (44) 4.1

B-M-Z2 41.1 (5960) 9.42 (0.371) 6 6.6 (38) 4.3

A-P-Z2 34.0 (4930) 8.46 (0.333) 4 12.4 (71) 2.6

B-P-Z2 36.4 (5280) 8.38 (0.330) 4 11.0 (63) 2.5

A-M-Z4 30.7 (4450) 6.68 (0.263) 6 21.2 (121) 3.0

B-M-Z4 32.2 (4670) 7.44 (0.293) 6 18.0 (103) 3.4

A-P-Z4 40.6 (5890) 4.06 (0.160) 10 35.7 (204) 3.1

B-P-Z4 44.5 (6450) 4.55 (0.179) 10 37.8 (216) 3.4

C-P-Z4 46.8 (6780) 5.31 (0.209) 12 31.5 (180) 4.8

D-P-Z4 44.9 (6510) 5.41 (0.213) 12 45.2 (258) 4.9

E-P-Z4 29.2 (4230) 5.71 (0.225) 12 42.2 (241) 5.2

F-P-Z4 27.7 (4020) 5.28 (0.218) 12 50.1 (286) 5.0

a These strengths were obtained at the time of the specimen tests. See Table 2.3 for the 28-daystrengths.

b These values are the initial elastic stiffness as obtained from the slope of the load-displacement plotfor the initial excursion to +0.75 ~.

c See explanation below.

The ultimate displacement ductility, J.L u' for both precast Zone 2 specimens was 4. The ultimatedisplacement ductility for specimen A-M-Z2, monolithic Zone 2 specimen A, was reported incorrectly inRef. 1. As defined in Chapter 2, failure was based on the lateral load applied to the connection. However,

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II-u = 4 as reported in Ref. 1 for specimen A-M-Z2 was based on the load recorded in one of the beamsand not on the lateral load applied to the connection. Therefore, based on the lateral load applied to theconnection, II-u for A-M-Z2 was 6 instead of 4. As a result, it would appear that the precast Zone 2specimens achieved lower ultimate displacement ductilities than did the monolithic Zone 2 specimens.The yield displacements for the :Z:one 2 specimens, monolithic and precast, were approximately the same.However, the precast Zone 2 specimens were approximately 65% stiffer than the monolithic Zone 2specimens.

As shown in Table 4.1, all the Zone 4 precast specimens achieved higher ultimate displacement ductilitiesthan did the monolithic Zone 4 specimens. Although the precast specimens achieved higher ultimatedisplacement ductilities than did the precast specimens in Phase I, it cannot be stated with certainty thatthis increase is a result of moving the post-tensioning bars closer to the beam center. This is becauseof the unsymmetric loading of the specimens in Phase I. The precast Zone 4 specimens were also stifferthan the monolithic Zone 4 specimens - approximately 90% stiffer for precast specimens A and B, 95%stiffer for precast specimens C and 0, and 135% for precast specimens E and F. It would appear thatthe precast specimens post-tensioned with prestressing strands were stiffer and achieved slightly higherstory drifts at failure than did the specimens post-tensioned with post-tensioning bars. Also, theconnection stiffness increased when the post-tensioning bars were moved closer to the beam center.

4.2 Flexural Strength

The measured maximum and calculated ultimate moments are given in Table 4.2. The calculated valueswere based on an ultimate concrete strain of 0.003 and actual material properties. The calculated ultimatemoments for the monolithic speicimens had a factor of 1.25 applied to the steel yield stress to accountfor strain-hardening. No factor for strain hardening was used in calculating the moments for the precastspecimens. The experimental values were obtained by multiplying the peak load recorded in the beamload cell and the moment arm to the column face.

The measured maximum moments for the monolithic specimens were achieved at or close to the ultimatedisplacement ductility of the connections. This was also true for precast specimens A-P-Z2, B-P-Z2, A-PZ4, and B-P-Z4. However, the measured maximum moments for the precast specimens with the posttensioning bars/prestressing strands closer to the beam center (C-P-Z4 through F-P-~4) were achievedearlier in the tests • at II- =: 4 whereas II-u = 12.

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Table 4.2 Measured and Calculated Ultimate Moments.

Calculated Measured

Specimen f' a Ultimate Maximum Avg. Exp. Momc

Moment Momentb Calc. Ult. Mom

MPa (psQ kN-m (k-ft) kN-m (k-ft)

A-M-Z2 43.5 (6310) 68 (50) 69 & 80 (51 & 59) 1.10

B-M-Z2 41.1 (5960) 68 (50) 70 & 75 (52 & 55) 1.07

A-P-Z2 34.0 (4930) 46 (34) 52 & 54 (38 & 40) 1.15

B-P-Z2 36.4 (5280) 46 (34) 50 & 54 (37 & 40) 1.13

A-M-Z4 30.7 (4450) 132 (97) 148 & 144 (109 & 106) 1.11

B-M-Z4 32.2 (4670) 132 (97) 148 & 153 (109 & 113) 1.14

A-P-Z4 40.6 (5890) 155 (114) 176 & 186 (130 & 137) 1.16

B-P-Z4 44.5 (6450) 155 (114) 184 & 186 (136 & 137) 1.20

C·P-Z4 46.8 (6780) 145 (107) 169 & 171 (125 & 126) 1.17

D-P·Z4 44.9 (6510) 145 (107) 165 & 169 (122 & 125) 1.15

E-P-Z4 29.2 (4230) 111 (82) 138 & 136' (102 & 100) 1.24

F-P·Z4 27.7 (4020) 111 (82) 146 & 137 (108 & 101) 1.28

a These concrete strengths were obtained at the time of the specimen tests. See Table 2.3 for the28-day strengths.

b Moments are at the column face. There are two values because the specimens were interior joints.

As seen in the last column of Table 4.2, the precast specimens were as strong or stronger than theirmonolithic counterparts. When comparing the results of A-P-Z4 and B-P-Z4 with those of C-P-Z4 and D-PZ4, the reduction in strength caused by moving the post-tensioning bars closer to the beam centroid wasapproximately 8%. It also appears that the precast specimens post-tensioned with prestressing strandshad more "reserve" strength than did the precast specimens post-tensioned with post-tensioning bars an average of 26% increase over the calculated moment as opposed to 17%.

4.3 Failure Modes

The failure mode for the precast Zone 2 specimens was beam crushing and inability of the connectionto sustain additional load. This is unlike the failure mode for the monolithic Zone 2 specimens which failedpredominantly in shear in the column joint region. The difference in the failure mode is likely a result ofthe debonding of the strands in the column joint region which would reduce the joint stress. The beamcolumn opening for the precast Zone 2 specimens was approximately 5 mm (0.2 in). This opening size

65

is one-fifth of the opening size lor the precast Zone 4 specimens. There is insufficient data to determineif this is a result of the higher initial beam stress imposed on the Zone 2 specimens or if it is the resultof the lower loads experienced by these specimens.

The failure modes for all the pmcast Zone 4 specimens were similar to the failure modes for the precastZone 2 specimens. The precast beams sustained less cracking than did the monolithic specimens andno visible beam hinging was observed. However, more beam crushing and a wider opening between thebeam and column, approximaWly 50% greater, was observed in the precast specimens which had thepost-tensioning bars/prestressing strands closer to the beam centroid.

4.4 Energy Absorbed

A comparison of the energy absorbed by all the specimens to 6 ~J cycle 3 is given in Fig. 4.1. Thecomparison was made at this stage because this was the approximate point at which the monolithicspecimens failed. As shown in Ithe figure, the monolithic Zone 4 specimens absorbed more energy percycle than the precast Zone 4 specimens. The energy absorbed per cycle by the precast Zone 4specimens was comparable to the energy absorbed per cycle by the monolithic Zone 2 specimens.

Figure 4.2 shows the comparison of the per cycle energy absorbed for all the precast Zone 4 specimens.As seen in the figure, specimens E-P-Z4 and F-P-Z4 performed the best and specimens A-P-Z4 and8-P-Z4 performed the worst in terms of energy absorption characteristics. The per cycle energy absorbedincreased by an average of 45% with a standard deviation of 24% when the post-tensioning bars weremoved closer to the beam cent,er. This increase is likely due to the increased crushing of the beamconcrete as observed during thEl test. An increase in the per cycle enery of an average of 30% with astandard deviation of 22% was noted when prestressing strands were used in place of post-tensioningbars. As seen by the large stand.:trd deviations, the percent increase in per cycle energy absorbed variedquite a bit. In spite of the improved performance, the per cycle energy absorbed by the precastspecimens, E-P-Z4 and F-P-Z4, was only an average of approximately 60% of that absorbed by themonolithic Zone 4 specimens. This is because the hysteresis curves for the all the precast Zone 4specimens were still severely pinched. This pinching may be a result of debonding of the prestressingstrands as observed during the test.

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.. -------

1 kN-m =8.85 k-in

20

I~ A-M-Z2 &B-M-Z2

• A-M-Z4 & B-M-Z416 -t • a A-P-Z2 & B-P-Z2

_II A-P-Z4 &B-P-Z4

[] C-P-Z4&D-P-Z4- 12 ~ I I liD E-P-Z4 &F-P-Z4EI

~en -...., >-

C)cr:w 8zw

4

o 1-= = ,

1 2 3 4 5 6 7 8

CYCLE NUMBER

Fig. 4.1 Comparison of cyclic energy absorbed to 6 Ii. Y' cycle 3.

1 kN-m =8.85 k-in20 -

• PTZ4A & B

o PTZ4C& 0

BI PT Z4 E & F

4

:2345678910111213141516

CYCLE NUMBER

Fig. 4.2 Cyc:lic energy absorbed by precast Zone 4 specimens.

Fig. 4.3 shows a comparison of the cyclic energy absorbed to failure by the Zone 2 specimens. As shownin Fig. 4.2. the monolithic and precast Zone 2 specimens absorbed similar amounts of energy per cycleuntil failure occurred. Again, thme is insufficient data to determine if the higher level of initial prestresscaused this improved behavior.

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69

The effect of moving the post-tensioning bars closer to the beam centroid (C-P-Z4 and D-P-Z4 vs. A-P-Z4and 8-P-Z4) on the cumulative energy absorbed was an increase of approximately 80 %. This increaseis due largely to the increased crushing of the beam concrete.

The cumulative energy absorbed to failure by all the specimens is shown in Fig. 4.4, Precast specimensC through F performed better than did the monolithic Zone 4 specimens. This was because the precastZone 4 specimens failed at a higher displacement ductility than did the monolithic Zone 4 specimens.The cumulative energy absorbed to failure by specimens C-P-Z4 and D-P-Z4 was 45% greater than thatabsorbed by the monolithic Zone 4 specimens. Similarly, the cumulative energy absorbed to failure byspecimens E-P-Z4 and F-P-Z4 was 71 % greater. The cumulative energy absorbed to failure by specimensA·P-Z4 and 8-P-Z4 was, however, 20% less. The cumulative energy absorbed at various stages is givenin Table 4.3.

1 kN-m = 8.85 k-in

• A-M-Z2

o B-M-Z2

III A-P-Z2

~ B-P-Z2

87654

CYCLE NUMBER

32

Fig. 4.3 Cyclic energy absorbed by Zone 2 specimens.

Eze>C}a:wzw

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120 PTZ4E&F

100

E 80ZC>.ElCD

60c:w

CD>.~

"3 40E;;;,()

20

o2 3 4 5 6 7 8 9 10 11 12

Specimen

Fig. 4.4 Comparison of the cumulative energy absorbed.

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I1 kN-m = 8.85 k-in I

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Table 4.3 Cumulative Energy Absorbed.

Cumulative Energy Absorbed

Specimen ILu to Failure to 6 !:.y, cycle 3

kN-m (k-in) kN-m (k-in)

A-M-Z2 6 21.0 (186) 18.6 (165)8,b

B-M-Z2 6 23.0 (204) 24.0 (212)b

A-P-Z2 4 7.3 (65) 15.9 (141)

B-P-Z2 4 8.8 (78) 15.6 (138)

A-M-Z4 6 67.4 (597) 67.4 (597)

B-M-Z4 6 61.3 (543) 61.3 (543)

A-P-Z4 10 49.5 (438) 18.6 (165)

B-P-Z4 10 53.9 (477) 20.4 (181)

C-P-Z4 12 93.9 (831) 26.8 (237)

D-P-Z4 12 92.9 (822) 27.1 (240)

E-P-Z4 12 110.7 (980) 34.7 (307)

F-P-Z4 12 109.4 (968) 32.4 (287)

a Cumulative energy absorbed through 6 Av, cycle 2.b For purposes of comparison, the energy absorbed in the third cycle at 4 ~ was not included in this

summation as the Zone 4 specimens did not undergo this particular cycle.

4.5 Reinforcing Bar Yield

Table 4.4 shows the extent of reinforcing bar and tie yielding for all the specimens. For each specimen,all the beam reinforcing bars and three ties in each beam were instrumented. Each of beam reinforcingbar was instrumented at five locations along the bar.

71

Table 4.4 Reinforcing Bar Yield Length.

Specimen lLength of Yield Avg. Length of Seta Extent of Tie Yield

mm (in) mm (in) mm (in)

A-M-Z2 450 (17.7) 432 (17.0) 76 (3.0)

B-M-Z2 414 (16.3) 0 (0.0)

A-P-Z2 110 (4.3) 111 (4.4) 110 (4.3)

B-P-Z2 112 (4.4) 110 (4.3)

A-M-Z4 5:23 (20.6) 532 (20.9) 229 (9.0)

B-M-Z4 541 (21.3) 406 (16.0)

A-P-Z4 Hi6 (6.1) 271 (10.7) 178 (7.0)

B-P-Z4 3a7 (15.3) 42 (1.7)

C-P-Z4 3~13 (15.5) 365 (14.4) 42 (1.7)

D-P-Z4 3:':17 (13.3) 42 (1.7)

E-P-Z4 91- (3.7) 122 (4.8) 42 (1.7).)

F-P-Z4 148 (5.8) 42 (1.7)

a Two identical specimens malke a set.

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As expected and as shown in Table 4.4, the monolithic specimens exhibited a longer reinforcing bar yieldlength than did the precast spec:imens. However. among the precast specimens, the specimens post-tensioned with post-tensioning bars had longer reinforcing bar yield lengths than did those post-tensioned Iwith prestressing strands. It would appear that the strains were more concentrated at the column jointfor the precast specimens which were post-tensioned with prestressing strands.

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5.0 SUMMARY AND CONCLUSIONS

5.1 Summary

Phase II of the precast concrete beam-column connection experimental test program being conductedat NIST involved the testing of six precast concrete specimens - three sets with each set consisting of twoidentical specimens. Two sets, C-P-Z4 & D-P-Z4 and E-P-Z4 & F-P-Z4, were designed similarly to thePhase I specimens, A-P-Z4 &B-P-Z4, whose design was based on the 1985 UBC seismic Zone 4 criteria.The other set, A-P-Z2 &B-P-Z2. was designed based on the criteria for the monolithic Zone 2 specimens.Again, the design of the monolithic Zone 2 specimens were based on the 1985 UBC seismic Zone 2criteria

The objective of the overall test program was to develop an economical moment-resistant precastconcrete beam-to-column connection in seismically active regions. The primary goal in Phase I was toidentify a viable precast concrete connection. The emphasis of Phase II was to improve the energyabsorption characteristics of the precast concrete connection identified in Phase I. '

The two parameters studied in Phase II were type of material used to post-tension the precast specimensand the location of the post-tensioning force. In reference to the first parameter, post-tensioning barswere used for specimens C-P-Z4 & D-P-Z4 while prestressing strands were used for specimens E-P-Z4& F-P-Z4 and A-P-Z2 & B-P-Z2. With regard to the second parameter, the post-tensioning bars weremoved closer to the beam center for specimens C-P-Z4 & D-P-Z4. These specimens were identical tospecimens A-P~Z4 & B-P-Z4 except for the location of the post-tensioning bars.

The construction of the precast concrete specimens was similar to the Phase I precast concretespecimens. A 25 mm (1 in) wide construction joint was filled with a fiber reinforced grout. The initialbeam prestress was 10.5 MPa (1.5 ksi) for the precast Zone 2 specimens and 7.0 MPa (1.0 ksi) for theprecast Zone 4 specimens.

Comparisons were made between the specimens in this phase and also with specimens in Phase I. Thecomparisons were made based on strength, energy absorption, and ductility of the connection. Thefollowing section presents the conclusions drawn based on Phase I and Phase II test results.

5.2 Conclusions

Failure of all the precast concrete specimens in Phase II was similar and was a result of the inability ofthe connection to sustain additional load. It was characterized by beam crushing and an openingbetween the beam and column. Other than fine cracks in the column connection region, this region didnot suffer additional distress. This failure mode was the same as that experienced by the precastspecimens in Phase I with the exception of a 50% increase of the beam-column opening for the Zone 4specimens. The width of the opening does not appear to be influenced by the type of post-tensioningsystem (post-tensioning bars or prestressing strands) used to connect the precast elements.

Unlike the monolithic Zone 2 specimens which failed predominantly in shear in the column joint region,the precast Zone 2 specimens did not experience severe joint distress. This was likely due to thedebonding of the prestressing strands in the column joint which lessened the joint stress.

The ultimate displacement ductilities for the precast Zone 2 specimens, J.Lu = 4, were lower than thatobtained for the monolithic Zone 2 specimens, JLu = 6. As a result, the average story drift at failure was

73

2.5% for the precast Zone 2 specimens and 4.2% for the monolithic Zone 2 specimens. The precast Zone2 specimens were approximately 65% stiffer than the monolithic Zone 2 specimens.

Ultimate displacement ductilities for the precast Zone 4 specimens were 12. These values were slightlyhigher than those achieved by precast specimens A-P-Z4 and B-P-Z4 (Phase I), JLu = 10. However, dueto the unsymmetrical loading of specimens A-P-Z4 and B-P-Z4, this increase in displacement ductilitycannot be conclusively attributEld to the change made in this test phase, Le. moving the post-tensioningbars closer to the beam center. The average story drift at failure for specimensC-P-Z4 and D-P-Z4 was4.9% and was approximately 50% greater than for the monolithic Zone 4 specimens. Similarly, theaverage story drift at failure for E-P-Z4 and F-P-Z4 was 5.1 % and was 60% greater than for the monolithicZone 4 specimens. In general, the precast specimens post-tensioned with post-tensioning bars wereapproximately 90% stiffer than the monolithic Zone 4 specimens and the precast specimens posttensioned with prestressing strands were 135% stiffer than the monolithic Zone 4 specimens.

With reference to the connection strength, the precast specimens, Zone 2 and Zone 4, performedsatisfactorily and as well as tho monolithic specimens. It appears that the precast specimens posttensioned with prestressing strands had more "reserve" strength than did the precast specimens posttensioned with post-tensioning bars. On average, the measured maximum moments for the precast Zone4 specimens post-tensioned with strands were 26% greater than the calculated values while the averagevalues for precast Zone 4 specimens post-tensioned with bars were 17% greater than the calculatedvalues. In addition, moving the post-tensioning force closer to the beam center does not appear to havea significant adverse effect on the connection strength.

As in Phase I, the per cycle energy absorbed by the precast Zone 4 specimens was much less than theper cycle energy absorbed by the monolithic Zone 4 specimens. However, improved energy absorptioncharacteristics due to the changeis made in this test phase were evident. The per cycle energy absorptionincreased by 45% when the post-tensioning bars were moved closer to the beam center. An increaseof 30% was noted when prestressing strands were used instead of post-tensioning bars. However, theper cycle energy absorbed by thEt specimens E-P-Z4 and F-P-Z4 (the precast specimens which performedbest with respect to per cycle energy absorbed) was only 60% of that for the monolithic Zone 4specimens. The poor performance of the precast Zone 4 specimens with respect to the per cycle energyabsorption is a result of the severely pinched hysteresis curves for these specimens. Debonding of theprestressing strands may have c:ausedthe pinching of the hysteresis curves. In contrast, the precastZone 2 specimens performed as well as the monolithic Zone 2 specimens in terms of per cycle energyabsorbed until failure occurred.

The cumulative energy absorbed by precast Zone 4 specimens C through F was greater than thecumulative energy absorbed by tlhe monolithic Zone 4 specimens. With reference to the monolithic Zone4 specimens, the cumulative energy absorbed by precast specimens C and 0 was 45% greater and forprecast specimens E and F the increase was 70%. This is in contrast to precast specimens A and B(Phase I) which had an average cumulative energy absorption than was 20% lower than the monolithicZone 4 specimens.

Although the per cycle energy absorbed by the precast Zone 2 specimens was similar to the monolithicZone 2 specimens, the cumulativl:l energy absorbed by the precast specimens was less than that for themonolithic Zone 2 specimens because the precast specimens failed at a lower displacement ductility.

Based on the, above findings, thEl effect of moving the post-tensioning force closer to the beam centerimproves the energy absorption c;haracteristics of the connection with little effect on the strength of theconnection. The use of prestressing strands as opposed to the use of post-tensioning bars seems toimprove the energy absorption characteristics of the connection and seems to increase the "reserve"strength of the connection. Although the energy absorption characteristics were improved, the per cycle

74

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-IIIIIIIII•

energy absorbed is still poor when compared to the monolithic connections. The precast Zone 2specimens did not perform as well as the monolithic Zone 2 specimens in terms of the ductility andcumulative energy absorption. However, the failure mode of the precast Zone 2 specimens was moredesirable than the failure mode of the monolithic Zone 2 specimens.

75

•II

. IIIIIIIIIIIII

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REFERENCES

1. Cheok, G. S. and Lew, H. S., 'Performance of 1/3-Scale Model Precast Concrete Beam-ColumnConnections Subjected to Cyclic Inelastic Load', NISTIR 4433, National Institute of Standards andTechnology, Gaithersburg, MD, October, 1990.

2. Woodward, K and Rankin, F., 'The NBS-Tri-Directional Tst Facility', NBSIR 84-2879, National Bureauof Standards, Gaithersburg, MD, May, 1984.

77

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NIST·114A(REV. 3-90)

U.S. DEPARTMENT OF COMMERCENATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BIBLIOGRAPHIC DATA SHEET

I\...

1. PUBUCATION OR REPORT NUMBER

NISTIR 45892. PERFORMING ORClANIZATION REPORT NUMBER

3. PUBUCATION DATEJUNE 1991

4. TI1l.E AND SUBTI1l.E

Performance of l/3-Scale Model Precast Concrete Bearn-Colurnn Connections Subjected toCyclic Inelastic Loads - Report No. 2

5. AUTHOR(S)

Geraldine S. CheckH. S. Lew

8. PERFORMING ORClANIZATION (IF ",OINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTIIENT OF COMMERCENATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGYQAlTliERSBURG. MD 2Cl89I

9. SPONSORING ORClANIZATlON NAME AND COMPL£TE ADDRESS (STREET, CITY, STATE, ZIp)

10. SUPPLEMENTARY NOTES

7. CONTRACTIGRANT NUMBER

a. TYPE OF REPORT AND PERIOD COVERED

N'I sr CATE.(.,olC" '# j 40

-III

11. ABSTRACT (A 200-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBUOGRAPHY ORUTERATURE SURVEY, MENTION IT HERE.)

--DResults are presented from the experimental test program on precast concrete beam-columnconnections subjected to inelastic cyclic loads being conducted at the National Instituteof Standards and Technology. This report is the second in a series and covers the testresults from Phase II of a three phase program. The objective of the test program is todevelop an economical moment resistant precast beam-column joint for high seismic zones '''--'.''".-"""'- -~"~-."",...-~'!llI..-·~~,..~-a.,~;:,~..,..,,"..,,~""~JI.r'W.~~_~~_:;.:·,"I\:~~=O'l~_~.... "U,I'.-~~':''t".''''!'C''~''''''~' , ... " .."..1

(Test specimens are 1/3-scale models of a prototype i~teri~r-"'concrete~"'oeam:'coi~n

connection. The 1985 UBC design criteria for seismic Zones 2 and 4 were used. Sixspecimens were tested. The experimental variables include the location of the posttensioning force and the type of post-tensioning tendons used. Comparisons of theperformance among these specimens are made. Comparisons with the monolithic specimens

...,(.P"hase-I=+R:e'f':""~l'}) are also presented. These comparisons are made based on the failuremode, energy absorption characteristics, strength and ductility of the connection. ~.~~=-~~

"'"'1'.

12. KEY WORDS (I TO 12 ENTRIES; ALPHABETICAL ORDER; CAPlTAUZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

bearn-colurnn: concrete: connections: cyclic loading: ductility: energy absorption: joints:moment resistance: post-tensioning: precast concrete.

II

13. AVAILA8lUTY

~ UNUIlITED

I-- FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS).

ORDER FROII SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT P'UNT1NG OFFICE,WASHINGTON, DC 20402.

~ ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTISl. SPRINGFIELD, VA 22111.

ELECTRONIC FORM

14. NUMBER OF PRINTED PAGES

84

15. PRICE

A05

· , " '.. " '," .,'.l. ~. ~ • .' • , •• '. ,.'! , ~ ",' 1',,' 1 • ;~

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performance of 1/3-scalemodel precast concrete beam

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