Experimental research on the flexural behavior of GFRP bar-reinforced composite beams with different shapes of prefabricated UHPC formwork

In this paper, the flexural behavior of eight composite beam with prefabricated permanent ultrahigh-performance concrete (UHPC) formwork and reinforced with glass fiber reinforced polymer (GFRP) bars were investigated based on four-point bending test and calculation. The types of prefabricated permanent UHPC formwork, bottom formwork thickness, and interface treatment methods were studied as experimental variables. It was found that the cracking load of beams with prefabricated permanent UHPC formwork increased by 77.4%-130.8 % compared with that of the reference beam. However, the ultimate bearing capacities of these composite beams, except for those of the beam with two-sided UHPC formwork and that with bottom UHPC formwork with a thickness of 50 mm (no debonding and an increase of 19.0 %), decreased by a maximum of 36.7 % due to the partial debonding between the prefabricated permanent UHPC formwork and core concrete. The overall performance of the composite beam improved as the bottom formwork thickness increased and the interface treatment existed. Based on the test re-sults, a simplified calculation method was developed to predict the cracking moment of composite beams with UHPC formwork. The cracking moment obtained by the proposed calculation method matches the experimental results.