Cyclic Evaluation of Severely Damaged RC Frames Repaired and Strengthened through FRP-Wrapped Coupler-Box Confinement
Publication: Journal of Composites for Construction
Volume 26, Issue 3
Abstract
The present study is focused on the retrofitting solution and its verification through experimental investigation for the two most common catastrophic modes of failure in reinforced concrete (RC) frame buildings, namely, buckling of reinforcing bars in the plastic hinge region of columns and shear failure of beam–column joints. The first mode of failure is retrofitted with interlinked coupler-box assemblies, while the second mode is repaired with external carbon fiber–reinforced polymer (CFRP) wrapping. The efficiency of the proposed retrofitting technique is evaluated by the hysteresis behavior, failure mechanism, and performance index parameters of the re-established frame, which are compared with the results of the initially tested bare frame. The recommended mechanism restricts the restored frame section against any possible movement or rotation and helps by a subsequent shift in yield location. The prime advantage of the proposed technique is that it prevents the possible slip of rebar from the sleeve, which is intercepted by the interlinking process, and eliminates the formation of inclined shear cracks at beam–column joints restricted by externally wrapped CFRP composites. The synergic effect of coupler-box and CFRP enhances the overall performance of the re-established frame by keeping the frame sections intact even after a lateral drift of 6%, which is relatively higher than the collapse prevention drift level, i.e., 4% as per FEMA guidelines. The obtained test results reveal the capability of CFRP and coupler-box assemblage as a possible futuristic approach for retrofitting outmoded RC building frames, in which buckling in longitudinal rebars of columns at their respective plastic hinge locations is inevitable.
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Acknowledgments
The authors acknowledge the research funding received from the Ministry of Earth Sciences, New Delhi, India (MoE-1274-EQD).
Notation
The following symbols are used in this paper:
- Afrp,j
- cross-sectional area of a CFRP wrap crossing the joint;
- bj
- breadth of the beam–column joint;
- D
- column dimension in the loading direction;
- dj
- depth of the beam–column joint;
- Efrp
- elastic modulus of the CFRP laminate;
- ffrp
- ultimate unidirectional tensile strength of the composite;
- ffrp,deb.
- debonding stress in FRP;
- fh
- confining pressure provided by transverse steel reinforcement;
- fl
- lateral clamping pressure over the lap-splice length;
- fy
- yield stress of the reinforcing bars;
- compressive strength of confined concrete;
- Lc
- length of the coupler sleeve;
- tc
- wall thickness of the coupler sleeve;
- tfrp,c
- design thickness of the CFRP laminate near the column hinge;
- tfrp,j
- design thickness of the CFRP laminate at the beam–column joint region;
- Vo
- column shear demand based on full flexural over strength;
- Vc
- shear contribution of concrete;
- VN
- shear contribution of applied axial load “N”;
- Vs
- shear contribution by steel reinforcement;
- νfrp,j
- contribution of FRP to joint shear strength;
- Ø
- diameter of the rebar;
- Øinner
- inner bore diameter of the coupler sleeve;
- Øbolt
- diameter of the external bolt;
- ϕv
- shear capacity reduction factor;
- ϕf
- flexural capacity reduction factor;
- β
- angle of inclination between FRP wrap and column axis;
- θ
- angle between critical diagonal crack and column axis;
- ɛcu
- ultimate concrete strain based on the level of confinement by a composite jacket;
- ɛfrp
- ultimate unidirectional failure strain of the composite in tension;
- ɛyy
- strain in the longitudinal direction of the rebar due to tensile loading measured using DIC;
- ɛ1
- superficial principal strain in the lateral direction measured using DIC; and
- ξhyst
- equivalent viscous damping ratio/coefficient.
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© 2022 American Society of Civil Engineers.
History
Received: Jun 30, 2021
Accepted: Jan 2, 2022
Published online: Feb 23, 2022
Published in print: Jun 1, 2022
Discussion open until: Jul 23, 2022
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