Flexural and Serviceability Behavior of Concrete Beams Reinforced with Ribbed GFRP Bars
Publication: Journal of Composites for Construction
Volume 26, Issue 5
Abstract
Glass fiber-reinforced polymer (GFRP) bars are used as internal reinforcement in many structural applications. The structural performance of GFRP-reinforced concrete elements is dependent on the physical and mechanical properties of GFRP reinforcement. There is a lack of experimental data on the flexural behavior of concrete beams reinforced with ribbed GFRP bars. This study evaluates the flexural strength and serviceability performance of concrete beams reinforced with ribbed GFRP bars. A total of 11 GFRP-reinforced concrete beams with dimensions of 4,350 × 400 × 200 mm (length × height × width) were constructed and tested under a four-point loading test setup. The main test parameters were the concrete cover, reinforcement ratio, bar spacing, and confinement due to the transverse reinforcement in the bending zone. The results uantify the effect of increasing the reinforcement ratio on the increase in the ultimate capacity and the reduction in deflection at the service and ultimate stages. In addition, the results showed that the increase in the confinement in the bending zone due to closely spaced stirrups resulted in a higher ductility index and ultimate capacity with no considerable effect on the postcracking stiffness of the beams. Moreover, based on the experimental results, the accuracy of deflection equations available in design codes and guidelines is evaluated and discussed.
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Acknowledgments
The authors acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) and MST Rebar Inc. (formerly B&B FRP Manufacturing Inc.) for their financial support. The authors thank the technicians in the structures laboratory at Concordia University for their assistance during the experimental work. The first author acknowledge the support of Mr. Islam Elsayed Nagy during the testing phase of this study.
Notation
The following symbols are used in this paper:
- a
- shear span measured from the center of the support to the point load;
- Af
- total area of the GFRP bars;
- b
- width of the rectangular cross section;
- c
- distance from the extreme compression fibers to the neutral axis;
- Cc
- curvature factor in the deformation-based approach;
- Cd
- deflection factor in the deformation-based approach;
- Cs
- ductility strength factor;
- d
- distance from the extreme compression fibers to the center of the tensile reinforcement;
- Ec
- concrete modulus of elasticity;
- Ee
- elastic absorbed energy;
- Ef
- GFRP reinforcement elastic modulus;
- Et
- total absorbed energy;
- specified compressive strength of the concrete;
- ffu
- design tensile strength of the GFRP bars;
- fr
- concrete tensile strength;
- Icr
- transformed moment of inertia of the equivalent cracked concrete section;
- Ie
- effective moment of inertia of the cross section;
- Ig
- gross moment of inertia of the cross section;
- J
- deformability performance factor;
- k
- ratio between the neutral axis and reinforcement depths;
- L
- support-to-support span of the member;
- Lg
- distance measured from the support to the cracking moment point in a simply supported beam;
- Ma
- applied moment on the member;
- Mc
- moment at a concrete compressive strain of 0.001;
- Mcr
- cracking moment;
- Ms
- moments at different serviceability limit states;
- Mult
- ultimate moment capacity of the section;
- nf
- ratio between the GFRP and concrete elastic moduli;
- P
- acting load on the member;
- P1
- cracking load;
- P2
- load at the beginning of concrete compression crushing in the overreinforced sections;
- S1
- initial slope of the loading curve before cracking;
- S2
- secant slope of the moment–deflection curve after cracking;
- S3
- unloading slope of the elastic region from the failure point;
- yb
- distance from the extreme tensile concrete fibers to the neutral axis;
- α1
- ratio of the average of the equivalent stress block to the concrete compressive strength;
- β1
- factor converting the actual stress diagram along the cross section to an equivalent rectangular stress block;
- βc
- tension stiffening factor;
- γ
- factor accounting for the variation in stiffness along the member length;
- δmax
- maximum midspan deflection at the applied load;
- Δu
- maximum deflection at the ultimate moment;
- Δɛ = 0.001
- deflection at a concrete compressive strain of 0.001;
- ɛc
- concrete compressive strain at any acting moment;
- ɛcu
- ultimate concrete compressive strain;
- ɛf
- GFRP tensile strain at any acting moment;
- η
- ratio of the difference between the gross and cracked moment of inertia to the gross moment of inertia;
- μd
- deformation-based ductility index;
- μe
- energy-based ductility index;
- ρfb
- balanced reinforcement ratio;
- φm
- curvature of the beam;
- φu
- curvature at the ultimate moment;
- φɛ = 0.001
- curvature at a concrete compressive strain of 0.001;
- ψc
- curvature at a concrete compressive strain of 0.001; and
- ψult
- curvature at the ultimate moment.
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Published In
Journal of Composites for Construction
Volume 26 • Issue 5 • October 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Dec 21, 2021
Accepted: May 26, 2022
Published online: Aug 9, 2022
Published in print: Oct 1, 2022
Discussion open until: Jan 9, 2023
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