Experimental Study on GFRP-Reinforced Concrete Closing Knee Joints

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.