bond, anchorage, and developmentlength

CEE 3410 Design of Concrete StructuresSchool of Civil & Environmental EngineeringYonsei University, Seoul, Korea

9/17/2019

Bond, Anchorage, and Development Length

Kyoungsoo Park

CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])

Flexural Bond

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Concept of Bond Stress

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Applied Load = Resisting Force𝑓 𝐴 𝑢 𝜋𝑑 ℓ

𝑓𝜋𝑑

4 𝑢 𝜋𝑑 ℓ

ℓ𝑓 𝑑4𝑢

Embedment length, ℓ


Common Failure Mechanisms

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Splitting of Concrete


Development Length ( 𝒅)

Length of Embedment (Shortest Length) Necessary to develop the full tensile strength of the bar Bar stress can increase from zero to the yield stress

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ℓ


Splice & Anchorage

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CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])9/17/2019 7

Development Length for Tension Bars

Basic Equation

Reinforcement location factor, 𝛼 Horizontal reinforcement so placed that more than 300 mm of fresh

concrete is cast in the member below the development length or splice : 1.3 Other situations: 1.0

Coating factor, 𝛽 Epoxy-coated bars or wires with cover less than 3𝑑 or clear spacing less

than 6𝑑 : 1.5 All other epoxy-coated bars or wires : 1.2 Uncoated and zinc-coated (galvanized) reinforcement: 1.0

Reinforcement size factor, 𝛾 D 19 and smaller bars and deformed wires : 0.8 D 22 and larger bars : 1.0

ℓ0.9𝑑 𝑓𝜆 𝑓

·𝛼𝛽𝛾

𝑐 𝐾𝑑



Basic Equation

Lightweight aggregate concrete factor, λ When 𝑓 not specified : 1.3

When 𝑓 specified : .

1.0

When normal weight concrete is used : 1.0

Spacing or cover dimension, 𝑐 Use the smaller of either the distance from the center of the

bar to the nearest concrete surface or one-half the center-to-center spacing of bars being developed.

ℓ0.9𝑑 𝑓𝜆 𝑓

·𝛼𝛽𝛾

𝑐 𝐾𝑑



Basic Equation

Transverse reinforcement index , 𝐾 𝐾

. or 𝐾 0

Atr = Total cross-sectional area of all transverse reinforcement that is within the spacing s and that crosses the potential plane of splitting trough the reinforcement being developed, mm2

s = maximum spacing of transverse reinforcement within ldcenter to center, mm

n = number of bars or wires being developed along the plane of splitting

𝑐 𝑘𝑑 2.5

𝑓 8.3 MPaℓ

0.9𝑑 𝑓𝜆 𝑓

·𝛼𝛽𝛾

𝑐 𝐾𝑑



Simplified Equation

ℓ .

Modification factor

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Bars and Deformed Wires smaller than D19

Bars Largerthan No.22

Clear spacing of bars being developed or spliced 𝑑 , clear cover 𝑑 , and

stirrups or ties throughout ℓ not less than the Code minimum

ORClear spacing of bars being developed or

spliced 2𝑑 , clear cover 𝑑

0.8𝛼𝛽𝜆 𝛼𝛽𝜆

Other case 1.2𝛼𝛽𝜆 1.5𝛼𝛽𝜆

ℓ ℓ 𝑀𝑜𝑑𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟


Anchorage of Tension Bars by Hooks

Standard Dimensions Main Reinforcement

Stirrups and Ties

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4𝑑 60𝑚𝑚

12𝑑

𝒅𝒃

6𝑑

𝑑

𝐷16 smaller

12𝑑

𝑑

𝐷19, 𝐷22 or 𝐷25

𝒅𝒃

𝑑

𝐷25 or smaller

135°

Size of bar Minimum Inside radius𝐷10 ~ 𝐷25𝐷28 ~ 𝐷35𝐷38 larger

3 𝑑4 𝑑5 𝑑


Anchorage of Tension Bars by Hooks

Development Length

Modification Factors Concrete Cover

𝐷35 and smaller bar hooks with side cover (normal to plane of hook) not less than 70 mm, and for 90° hooks with cover on bar extension beyond hook not less than 50 mm : 0.7

Coating factor, 𝛽 Lightweight aggregate concrete factor, λ

Refer Table 5.3 (p. 184) & Concrete Design Standard (KCI)

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ℓ 0.24𝛽𝑑 𝑓

𝜆 𝑓 , ℓ 8 𝑑 , ℓ 150 𝑚𝑚



Development Length for Compression Bars

Development Length

Modification Factor Reinforcement in excess of that required by analysis:

Reinforcement enclosed within spiral Reinforcement not less than 6 mm diameter and not more than

100 mm pitch or within D13 ties spaced at not more than 100 mm on centers: 0.75

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ℓ 0.24 𝑑 𝑓

𝜆 𝑓0.043𝑑 𝑓



Concrete Cover

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Environmental Conditions and Structural TypeMinimum size

of concrete cover (mm)

Concrete not expose to

weather or in contact with

ground

Bean, column 40

Slab, Wall, Joists Bar smaller than D 35Bar lager than D 35

2040

Shell, folded plate 20

Concrete expose to earth or weather

Bar lager than D 29Bar smaller than D 25Bar smaller than D 16

605040

Concrete cast against and permanently exposed to earth 80Concrete cast underwater 100


ACI 318 Provisions

12.10 – Development of flexural reinforcement – General12.10.1 – Development of tension reinforcement by bending across the web to be anchored or made continuous with reinforcement on the opposite face of member shall be permitted.12.10.2 – Critical section for development of reinforcement in flexural members are at point of maximum stress and at points within the span where adjacent reinforcement terminates, or it bent. Provisions of 12.11.3 must be satisfied.12.10.3 – Reinforcement shall extend beyond the point at which it is no longer required to resist flexure for a distance equal to d or 12db, whichever is greater, except at supports of simple spans and at free end of cantilevers. 12.10.4 – Continuing reinforcement shall have an embedment length not less than ld beyond the point where bent or terminated tension reinforcement is no longer required to resist flexure.

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ACI 318 Provisions

12.11 – Development of positive moment reinforcement 12.11.1 – At least one-third the positive moment reinforcement in simple members and one-fourth the positive moment reinforcement in continuous members shall extend along the same face of member into the support. In beams, such reinforcement shall extend into the support at leads 6 in (150 mm)

12.12 – Development of negative moment reinforcement 12.12.2 – Negative moment reinforcement shall have an embedment length into the span as required by 12.1 and 12.10.3.12.12.3 – At least one-third the total tension reinforcement provided for negative moment at a support shall have an embedment length beyond the point of inflection not less than d, 12db, or ln/16, whichever is greater.

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Kyoungsoo Park ([email protected])

Thank You!

http://k-park.yonsei.ac.kr

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bond, anchorage, and developmentlength

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