Experimental Analysis of Shear Resisting Mechanisms in FRP RC Beams with Shear Reinforcement
Publication: Journal of Composites for Construction
Volume 24, Issue 5
Abstract
Owing to the unique mechanical characteristics and lack of plasticity of fiber-reinforced polymers (FRPs), relatively large strains can develop in FRP reinforced concrete (RC) elements at ultimate limit states and this can lead to different relative contributions of concrete and shear reinforcement to the total element's shear capacity. This paper examines the development and relative contribution of the main shear resisting mechanisms in concrete beams with different overall depths and reinforced with longitudinal and transversal FRP reinforcement. Complementary strain measurements obtained from digital image correlation (DIC) and strain gauges are presented and discussed thoroughly. Although current FRP shear design approaches rely on the assumption that the contributions of concrete and shear reinforcement are constant up to failure, their relative magnitude is found to vary with increasing crack width. The experimental results indicate that, when minimum shear reinforcement is provided, current shear models based on a fixed truss angle approach tend to overestimate the contribution of concrete and underestimate the contribution of shear reinforcement. The use of a variable angle truss model, along with an appropriate reduction in the contribution of concrete, would lead to a more reliable estimate of the main shear resisting mechanisms and optimal design of the required amount of shear reinforcement.
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Acknowledgments
This research was funded by the EU FP7 Marie Skłodowska–Curie Initial Training Network endure (Grant Agreement No. 607851). The authors would like to thank the European Commission for its financial support and for providing wide networking opportunities within the research community.
Notation
The following symbols are used in this paper:
- Afl
- total area of the longitudinal reinforcement;
- Afv
- total area of the shear reinforcement at given spacing;
- a
- length of the test shear span;
- a′
- length of the nontest shear span;
- bw
- width of the beam;
- d
- effective depth of the beam;
- dv
- effective shear depth of the beam;
- Ec
- modulus of elasticity of the concrete;
- Efl
- Young's modulus of longitudinal FRP reinforcement;
- Efv
- Young's modulus of shear FRP reinforcement;
- fFRPu
- ultimate strength of the shear link;
- concrete cylinder strength;
- ffb
- allowable strength of the bent portion of the FRP stirrup;
- ffu
- allowable stress in the shear reinforcement;
- Fsl,i
- experimental force developed in ith shear link;
- h
- overall depth of the beam;
- k1
- ratio between the shear load in the test shear span and applied load;
- km
- coefficient taking into account the effect of moment at section on shear strength;
- kr
- coefficient taking into account the effect of reinforcement rigidity on its shear strength;
- ks
- coefficient taking into account the effect of member size on its shear strength;
- L
- beam's clear span;
- Ma
- applied moment;
- Pult
- ultimate load applied;
- s
- spacing of the FRP shear links;
- Va
- applied shear force;
- Vc
- shear capacity provided by concrete;
- Vcon
- estimated experimental contribution of concrete;
- Vexp
- experimental shear capacity;
- Vf
- calculated shear strength provided by FRP shear links;
- Vs
- calculated shear strength provided by steel stirrups;
- Vscr
- experimental shear force in tested shear span at diagonal cracking;
- wmax,DIC
- maximum crack width measured through DIC;
- δscr
- deflection at Vscr, measured under the loading point;
- ɛl,max
- maximum strain in the main longitudinal reinforcement;
- ɛt,max,DIC
- maximum strain in the shear links measured through DIC;
- ɛt,max
- maximum strain in the shear links;
- ɛti
- experimental strain measured in ith shear link (measured through DIC or strain gauge);
- ɛx
- strain at beam middepth;
- θ
- angle of inclination of the principal diagonal compressive stresses;
- λ
- factor accounting for concrete density;
- ρfl
- longitudinal reinforcement ratio;
- ρfv
- vertical (shear) reinforcement ratio;
- φc
- resistance factor for concrete; and
- φf
- resistance factor for FRP reinforcement.
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Published In
Journal of Composites for Construction
Volume 24 • Issue 5 • October 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Apr 9, 2019
Accepted: Mar 9, 2020
Published online: Jun 17, 2020
Published in print: Oct 1, 2020
Discussion open until: Nov 17, 2020
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