Flexural behavior of GFRP bar-reinforced concrete beams with U-shaped UHPC stay-in-place formworks

Abstract

Poor durability of reinforced concrete structures in harsh marine environments is an intractable issue. Replacing steel bars with fiber-reinforced polymer (FRP) bars and utilizing ultrahigh-performance fiber concrete (UHPC) for the concrete cover can greatly increase the durability of such structures. A new hybrid GFRP bar reinforced concrete beam with a prefabricated U-shaped UHPC stay-in-place formwork was tested. Herein, nine beams—one reference beam and eight hybrid beams with prefabricated U-shaped UHPC stay-in-place formworks—were subjected to four-point bending tests. The test parameters included the existence of a U-shaped UHPC stay-in-place formwork, the GRFP bar reinforcement ratio, the core concrete strength, and the bottom longitudinal reinforcement type. Experimental results showed that the hybrid beams had approximately 93.8–228.2% higher cracking loads and the hybrid beams (except beams U2 and U5) had approximately 5.9–19.0% higher ultimate loads than the reference beam. Increasing the GFRP reinforcement ratio improved the cracking load and bearing capacity of the hybrid beams, and the ultimate load increased with increasing core concrete strength. Premature failures in some hybrid beams due to partial debonding occurred between the U-shaped UHPC stay-in-place formwork and core concrete. Thence, the partial debonding should be avoided in further studies by proposing a more effective interfacial bonding method for the hybrid beam.