Confinement Properties of GFRP-Reinforced Concrete Circular Columns under Simulated Seismic Loading
Publication: Journal of Composites for Construction
Volume 25, Issue 2
Abstract
Columns in earthquake-resistant reinforced concrete (RC) structures need to be adequately confined to provide satisfactory levels of stability and deformability. In circular RC columns, confinement can be provided by spirals or hoops. This paper presents an investigation of the glass fiber-reinforced polymer (GFRP) confinement reinforcement requirements in columns of moment-resisting frames. Six full-scale circular RC columns were tested under simultaneous axial loading and unidirectional cyclic lateral drift reversals. The studied parameters were longitudinal reinforcement type, transverse reinforcement shape and pitch, and axial load level. Test results indicated that the maximum spiral pitch of one-fourth the gross diameter of the column as per the Canadian code for FRP-RC structures was reasonable and sufficiently conservative. In addition, GFRP circular hoops require larger lap splice length than that specified by the Canadian Highway Bridge Design Code to provide comparable confinement to GFRP spirals. The experimental results were estimated by a simplified method based on available confinement models, codes and guidelines for FRP-RC structures. It is recommended to consider the compressive strength of GFRP longitudinal bars with a compressive strain limit of 0.002 in circular GFRP-RC columns.
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Acknowledgments
The authors would like to express their sincere gratitude to the Natural Science and Engineering Research Council of Canada (NSERC) and the University of Manitoba Graduate Fellowship (UMGF) for financial support. The GFRP reinforcement was generously provided by Pultrall Inc. The authors would also like to acknowledge the assistance received from the technical staff of W. R. McQuade Structures Laboratory at the University of Manitoba.
Notation
The following symbols are used in this paper:
- AF
- area of FRP main reinforcement;
- Ag
- gross area of the column section;
- dAc
- area of unconfined concrete within the layer under consideration;
- dAcc
- area of confined concrete within the layer under consideration;
- dc
- depth of centroid of layer under consideration from the extreme compression fiber;
- dn
- depth of compression zone;
- specified concrete compressive strength;
- P
- axial load applied on column;
- Po
- nominal unconfined axial load capacity of GFRP-RC column;
- α1
- ratio of average stress in rectangular compression block to the specified concrete strength;
- β1
- ratio of depth of rectangular compression block to depth of the neutral axis;
- βc
- concrete strength multiplier suggested for GFRP-RC circular columns;
- ɛbot
- strain at outermost GFRP bar in tension;
- ɛc
- strain at centroid of layer under consideration;
- ɛtop
- strain at extreme compression fiber;
- ρf
- longitudinal reinforcement ratio for FRP-RC columns;
- ρst
- longitudinal reinforcement ratio for steel-RC columns;
- σc
- stress in unconfined concrete corresponding to strain ɛc;
- σcc
- stress in confined concrete corresponding to strain ɛc; and
- ϕc
- material resistance factor for concrete.
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Published In
Journal of Composites for Construction
Volume 25 • Issue 2 • April 2021
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Jun 4, 2020
Accepted: Oct 9, 2020
Published online: Dec 18, 2020
Published in print: Apr 1, 2021
Discussion open until: May 18, 2021
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