Shear Friction and Strut-and-Tie Modeling Verification for Pier Caps
Publication: Journal of Bridge Engineering
Volume 26, Issue 9
Abstract
This study reports on experimental test results of reinforced concrete pier caps with different shear spans to effective depth ratios (a/d) of 0.5, 1, and 1.5. Each test specimen is then designed theoretically using both shear friction (SF) and strut-and-tie modeling (STM) approaches, according to Section 16.5 and Chapter 23 of ACI 318-14, respectively, and the results are compared with the pier caps experimental test results. The cracking load, failure load, deflection, crack pattern, crack width, steel reinforcement strains, concrete surface average strains, and failure modes are observed, recorded, and discussed. The experimental load capacities are compared with the theoretical load capacities of SF and STM. Experimental test results indicate that both STM and SF are conservative approaches and STM is more conservative than SF. The reason for this is because they do not take secondary reinforcement into direct consideration. That is why, a model is proposed, modifying STM, for estimating the ultimate capacity of pier caps based on calculating the strength of concrete and secondary reinforcement separately that gave more realistic results.
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Data Availability Statement
Some or all data, models, or codes generated or used during the study are available from the corresponding author by request, including
•
data from concrete and steel strain gages, dial gauge, and load cells,
•
observed crack width measurements,
•
concrete and reinforcing steel material property data, and
•
STM analysis calculations.
Acknowledgments
The authors are grateful to the staff of the Civil Engineering Department in the College of Engineering at the University of Diyala for their outstanding moral support.
Notation
The following symbols are used in this paper:
- Ab
- area of reinforcing bars, mm2;
- Ah
- area of secondary horizontal reinforcement, mm2;
- As
- area of main longitudinal tension reinforcement, mm2;
- Av
- area of secondary vertical reinforcement, mm2;
- a
- shear span measured from the vertical face of the pier to the load center, mm;
- b
- width of pier cap, mm;
- d
- effective depth of pier cap, distance from the centroid of longitudinal tension reinforcement to the extreme compression fiber, mm;
- Ec
- modulus of elasticity of concrete, MPa;
- Es
- modulus of elasticity of steel reinforcement, MPa;
- cylinder compressive strength of concrete, MPa;
- fct
- indirect tensile strength (splitting tensile strength), MPa;
- fr
- modulus of rupture, MPa;
- fy
- yield stress of main steel reinforcement, MPa;
- fyh
- yield stress of secondary horizontal reinforcement, MPa;
- fyv
- yield stress of secondary vertical reinforcement, MPa;
- h
- overall depth of pier cap, mm;
- jd
- distance between the centers of the top and bottom nodes, mm;
- L
- total length of pier cap, mm;
- Lb
- length of the load-bearing block, mm;
- P
- ultimate load failure, kN;
- Pcr-diag
- first diagonal cracking load, kN;
- Pcr-flex
- first flexural cracking load, kN;
- PSF
- theoretical load according to Chapter 16.5 and Chapter 22.9, shear friction, ACI 318M-14, kN;
- PSTM
- theoretical load according to Chapter 23, ACI 318M-14, strut-and-tie method, kN;
- Sh
- secondary horizontal reinforcement spacing, mm;
- Sv
- secondary vertical reinforcement spacing, mm;
- θ
- angle between the axis of strut, compression diagonal, or compression field and the tension chord of the members;
- μ
- coefficient of friction;
- Δ
- displacement corresponding to the ultimate of pier cap, mm;
- Δdiag.crack
- displacement corresponding to the first diagonal crack load, mm;
- Δflex.crack
- displacement corresponding to the first flexural crack load, mm;
- ρ
- main reinforcement ratio;
- ρh
- secondary horizontal reinforcement ratio;
- ρv
- secondary vertical reinforcement ratio;
- a/d
- shear span to effective depth ratio; and
- c/c
- center to center, mm.
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© 2021 American Society of Civil Engineers.
History
Received: Nov 4, 2020
Accepted: Apr 23, 2021
Published online: Jun 23, 2021
Published in print: Sep 1, 2021
Discussion open until: Nov 23, 2021
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