Experimental Study on GFRP-Reinforced Concrete Closing Knee Joints
Publication: Journal of Composites for Construction
Volume 24, Issue 4
Abstract
Knee-joints are a common element in concrete structures, which may be problematic when reinforced with glass fiber-reinforced polymer (GFRP) bars. GFRP bends are significantly weaker than the straight portions due to transverse loading on fibers as well as nonstandardized manufacturing processes. The behavior of GFRP-reinforced knee-joints has not been previously studied. In the presented research, eight full-scale GFRP-reinforced concrete corner joint specimens were constructed and tested under monotonic closing loads. The specimens consist of a beam and column, which are connected and terminate at the joint. The experimental program was designed to study the effect of reinforcement ratio, confinement reinforcement, and corner geometry on the behavior of the joint. Increasing reinforcement ratio of bent bars through the joint altered the failure mode from bar rupture to diagonal strut failure; however, this had minimal effect on ultimate strength efficiency. The addition of confinement reinforcement in the joint resulted in a significant increase in ultimate strength efficiency and maximum deflection. Joints with altered geometry by including an interior chamfer performed better than the regular joint type; failure mode was altered to a nonbrittle failure and a marginal increase in strength efficiency was observed.
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Acknowledgments
The authors would like to acknowledge and thank the Ministry of Transportation of Ontario (MTO) for their financial support of this research program. The authors also extend their thanks to Pultrall Inc. for supplying GFRP reinforcement.
Notation
The following symbols are used in this paper:
- A
- area of GFRP reinforcement, mm2;
- a
- depth of equivalent rectangular stress block, mm;
- d
- distance from extreme compression fiber to centroid of tensile force, mm;
- concrete compressive strength, MPa;
- ffrp
- stress in GFRP reinforcement, MPa;
- fu
- ultimate tensile strength of FRP, straight portion, MPa;
- fu,bend
- ultimate tensile strength of FRP, bend, MPa;
- T
- tension force resultant, N;
- z
- distance between compression and tension force resultants, mm;
- ρ
- reinforcement ratio;
- ρb
- balanced reinforcement ratio; and
- ϕ
- FRP bar resistance factor, set to 1.
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Information & Authors
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Published In
Journal of Composites for Construction
Volume 24 • Issue 4 • August 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Jan 15, 2019
Accepted: Dec 23, 2019
Published online: Apr 22, 2020
Published in print: Aug 1, 2020
Discussion open until: Sep 22, 2020
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