Shear Behavior of Post-Tensioned Concrete Beams with Draped FRP Tendons and without Transverse Reinforcement
Publication: Journal of Composites for Construction
Volume 25, Issue 4
Abstract
To investigate the shear behavior of post-tensioned concrete beams with fiber-reinforced polymer (FRP) reinforcements, six large-scale post-tensioned beams without transverse reinforcement and with a shear span-to-effective depth ratio of approximately 3.0 were tested to failure. All beams were longitudinally reinforced with draped prestressed carbon FRP tendons and non-prestressed glass FRP bars. The test variables included the amount of flexural reinforcement and the prestressing level. With the aid of full-field measurement on the beam surface using digital image correlation, the kinematics of the critical shear crack of each beam were tracked. Two shear failure modes, including shear compression and shear tension, were observed in the tested beams. Generally, when the amount of flexural reinforcement increased, there was a corresponding increase in the maximum shear force. When the total prestressing force was increased from 360 to 440 kN, the shear cracking strength and the maximum shear strength increased by 6.9% and 10.0%, respectively. It was demonstrated that an arch mechanism formed in the tested FRP post-tensioned beams, although the contribution of aggregate interlock to the shear capacity was negligible. The predictions of the shear capacity calculated from various shear design models showed that the American and Japanese recommendations were highly conservative, whereas the Canadian recommendations were more consistent with the experimental results.
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Acknowledgments
The authors gratefully acknowledge the financial support provided by the Project of National Key R&D Plan of China (No. 2017YFC0703000), the National Natural Science Foundation (No. 51678433 and No. 52008165), and Changsha Municipal Natural Science Foundation (No. kq2014053).
Notation
The following symbols are used in this paper:
- Af
- area of the tensile FRP bar;
- Afp
- area of the prestressing FRP tendon;
- Ag
- total cross-sectional area of beam;
- bw
- web width of beam;
- d
- effective depth of beam;
- dv
- effective shear depth, taken as the greater of 0.9d or 0.72h;
- Ef
- modulus of elasticity of the FRP bar;
- Efp
- modulus of elasticity of the FRP tendon;
- Es
- modulus of elasticity of steel;
- specified compressive strength of concrete;
- fcd
- design compressive strength of concrete;
- fcr
- cracking strength of concrete;
- ffp0
- stress in prestressing tendon when strain in the surrounding concrete is zero;
- fmcd
- design compressive strength of concrete allowing for the size effect;
- ka
- factor accounting for the effect of arch action of shear strength of the member;
- km
- factor accounting for the effect of moment at a section of the member on its shear strength;
- kr
- factor accounting for longitudinal reinforcement;
- ks
- factor accounting for the effect of member size on its shear strength;
- lcr
- crack length;
- Md
- design bending moment;
- Mdc
- decompression moment;
- Mfa
- factored applied bending moment;
- Nd
- design axial compressive force;
- Nfa
- factored applied axial load;
- Np0
- factored applied axial load;
- Ped
- effective tensile force in prestressing tendons;
- sze
- equivalent value of the crack spacing parameter that accounts for influence of aggregate size;
- Vag
- shear contribution of aggregate interlock;
- Vcr
- shear cracking force;
- Vfa
- =factored applied shear force;
- Vn
- predicted shear capacity;
- Vp
- vertical component of the prestressing force;
- Vu
- experimental shear capacity;
- w
- shear crack width;
- αp
- angle between prestressing tendon acting as shear reinforcement and member axis;
- β
- factor accounting for aggregate interlock in concrete sections;
- Δ
- shear crack slip;
- ɛx
- longitudinal strain at middepth;
- ρfl
- longitudinal reinforcement ratio;
- σag
- normal stress acting on the cracked plane; and
- τag
- shear stress acting on the cracked plane.
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Published In
Journal of Composites for Construction
Volume 25 • Issue 4 • August 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Apr 16, 2020
Accepted: Feb 27, 2021
Published online: May 5, 2021
Published in print: Aug 1, 2021
Discussion open until: Oct 5, 2021
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