Bond Performance of GFRP Bar-Splicing in Reinforced Concrete Beams
Publication: Journal of Composites for Construction
Volume 26, Issue 2
Abstract
The bond between fiber-reinforced polymer (FRP) bars and concrete is the weakest link in the chain of parameters affecting the behavior of FRP-reinforced structures. In this study, eight glass fiber–reinforced polymer (GFRP)-reinforced concrete beams were tested in flexure. There were two control beams and six beams with lap splices. The first control had continuous rebars, whereas the second control had lap splices. A lap length of 40 times rebar diameter was used in tension in the constant moment region. The test variables included the spacing of confining stirrups (no stirrups, 100, and 50 mm) and a gap between rebars in the lap splice zone (0 and 18 mm). The test results revealed that the bond strength of GFRP rebars increases with the enhancement in the gap between rebars and the decrease in the spacing of confining stirrups. The available development length and bond-strength equations were modified to incorporate the effect of the GFRP rebar gap and spacing of confining stirrups in the lap zone. Besides the experimental program, nonlinear finite-element models were prepared to model the behavior of test beams and validate the proposed bond strength equations.
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Acknowledgments
The authors are grateful to the Deanship of Scientific Research, King Saud University, for funding through Vice Deanship of Scientific Research Chairs.
Notation
The following symbols are used in this paper:
- Afb
- area of cross section of one FRP rebar;
- Atr
- area of transverse reinforcement in the lap zone;
- C
- minimum of the concrete cover up to the center of rebars and 50% of the spacing of the rebars;
- CE
- environmental reduction factor;
- D
- damage curve parameter;
- db
- diameter of longitudinal rebars;
- dcs
- smaller of the distance of center of the rebar from the closest concrete surface and two-third of the center-to-center spacing the bars being developed in mm;
- Ef
- elastic modulus of FRP rebars;
- Es
- elastic modulus of steel;
- Et
- elastic modulus of stirrups;
- compressive strength of concrete;
- fbf
- design bond strength of concrete;
- fcr
- cracking strength of concrete in MPa;
- ff
- rebar stress at the end of the embedded length (=CE ffr);
- ffr
- required stress in FRP rebars;
- ffu
- tensile strength of FRP rebars;
- fR
- factor for rebar surface properties;
- fu
- ultimate strength of rebars;
- fy
- yield strength of rebars;
- fyv
- yield stress of confining stirrups;
- Gs
- shear modulus of the bond-slip relationship;
- hdmg
- damage curve parameter;
- k
- factor for the effect of non-contact lap;
- k1
- rebar location factor (=1.3 for horizontal rebars placed such that more than 300 mm of fresh concrete is cast below the rebars; and 1.0 for other cases);
- k4
- rebar surface factor (=ratio of the bond strength of the FRP rebar to that of a steel deformed rebar of the same cross-sectional area; =0.8 in the absence of experimental data);
- kc
- parameter;
- Kpre
- precracking stiffness;
- Kpost
- postcracking stiffness;
- Ktr
- parameter;
- L
- effective span of simply supported beam;
- Ld
- development length of rebar;
- le
- embedded length of rebar;
- Lp
- lap length of longitudinal rebars;
- n
- modular ratio;
- P
- point load applied on beam (total load = 2P);
- Pu
- ultimate point load applied on beam (total ultimate load = 2Pu);
- S
- spacing of confining stirrups provided along the rebar lap zone;
- Sr
- gap between rebars in the lap zone;
- u
- bond strength of spliced rebars with transverse reinforcement;
- uc
- bond strength of spliced rebars (without confining stirrups);
- umax
- peak bond stress;
- uv
- bond strength contributed by the confining stirrups;
- α
- top rebar modification factor;
- α1
- parameter;
- α2
- modification factor for bond strength;
- δs
- rebar slippage;
- δs,max
- slippage corresponding to the peak bond stress;
- Δu
- midspan deflection at ultimate state;
- ɛre
- experimental rebar strain at rupture;
- ɛfu
- rupture strain of GFRP rebars;
- γc
- material safety factor for concrete (=1.3 when ; =1.5 in all other cases); and
- strength reduction factor.
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History
Received: Jul 23, 2021
Accepted: Nov 17, 2021
Published online: Jan 27, 2022
Published in print: Apr 1, 2022
Discussion open until: Jun 27, 2022
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