bond, anchorage, and developmentlength
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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])
Concept of Bond Stress
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Applied Load = Resisting Forceπ π΄ π’ ππ β
πππ
4 π’ ππ β
βπ π4π’
Embedment length, β
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
Common Failure Mechanisms
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Splitting of Concrete
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
Development Length ( π )
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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β
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
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, πΌ 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, π½ Epoxy-coated bars or wires with cover less than 3π or clear spacing less
than 6π : 1.5 All other epoxy-coated bars or wires : 1.2 Uncoated and zinc-coated (galvanized) reinforcement: 1.0
Reinforcement size factor, πΎ D 19 and smaller bars and deformed wires : 0.8 D 22 and larger bars : 1.0
β0.9π ππ π
Β·πΌπ½πΎ
π πΎπ
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])9/17/2019 8
Development Length for Tension Bars
Basic Equation
Lightweight aggregate concrete factor, Ξ» When π not specified : 1.3
When π specified : .
1.0
When normal weight concrete is used : 1.0
Spacing or cover dimension, π 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.
β0.9π ππ π
Β·πΌπ½πΎ
π πΎπ
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])9/17/2019 9
Development Length for Tension Bars
Basic Equation
Transverse reinforcement index , πΎ πΎ
. or πΎ 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
π ππ 2.5
π 8.3 MPaβ
0.9π ππ π
Β·πΌπ½πΎ
π πΎπ
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
Development Length for Tension Bars
Simplified Equation
β .
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 π , clear cover π , and
stirrups or ties throughout β not less than the Code minimum
ORClear spacing of bars being developed or
spliced 2π , clear cover π
0.8πΌπ½π πΌπ½π
Other case 1.2πΌπ½π 1.5πΌπ½π
β β πππππππππ‘πππ ππππ‘ππ
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
Anchorage of Tension Bars by Hooks
Standard Dimensions Main Reinforcement
Stirrups and Ties
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4π 60ππ
12π
π π
6π
π
π·16 smaller
12π
π
π·19, π·22 or π·25
π π
π
π·25 or smaller
135Β°
Size of bar Minimum Inside radiusπ·10 ~ π·25π·28 ~ π·35π·38 larger
3 π4 π5 π
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
Anchorage of Tension Bars by Hooks
Development Length
Modification Factors Concrete Cover
π·35 and smaller bar hooks with side cover (normal to plane of hook) not less than 70 mm, and for 90Β° hooks with cover on bar extension beyond hook not less than 50 mm : 0.7
Coating factor, π½ Lightweight aggregate concrete factor, Ξ»
Refer Table 5.3 (p. 184) & Concrete Design Standard (KCI)
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β 0.24π½π π
π π , β 8 π , β 150 ππ
β β πππππππππ‘πππ ππππ‘ππ
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
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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β 0.24 π π
π π0.043π π
β β πππππππππ‘πππ ππππ‘ππ
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
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
CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
ACI 318 Provisions
12.10 β Development of flexural reinforcement β General12.10.1 β 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 β 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 β 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 β 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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CEE 3410 Design of Concrete StructuresKyoungsoo Park ([email protected])
ACI 318 Provisions
12.11 β Development of positive moment reinforcement 12.11.1 β 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 β Development of negative moment reinforcement 12.12.2 β Negative moment reinforcement shall have an embedment length into the span as required by 12.1 and 12.10.3.12.12.3 β 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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