Flexural behavior and crack width prediction of UHPC slabs reinforced with FRP bars

This paper aims to investigate the effects of FRP-bar configurations on the flexural behavior of the FRP-reinforced ultra-high-performance concrete (UHPC) deck slab and to propose the calculation method of crack width. Firstly, flexural tests were performed on six FRP-reinforced UHPC slab specimens with varying bar diameters, reinforcement ratios, cover thickness, and slab thick-nesses. The load-deflection responses, load-FRP strain relations, and cracking behavior are measured and discussed. The results show that under service loads, the maximum crack widths of all specimens are around 0.03 mm-0.04 mm, which is significantly less than the permitted 0.5 mm in international codes for FRP-reinforced structures. At similar reinforcement ratios, a small FRP-bar diameter with a corresponding reduced bar spacing increases the ultimate capacity and energy dissipation ability. The effects of FRP-bar configurations are minor under service loads, while beyond these loads decreasing the bar diameter is beneficial for reducing the bar strain and crack width. Subsequently, by developing a practical calculation method of the stress of FRP bar embedded in UHPC slab and calibrating the bond coefficient between FRP bar and UHPC against test data, an engineer-friendly calculation method of crack width is proposed. Comparisons be-tween predicted and experimental results indicate the proposed method is capable of producing accurate and safe predictions. The results may give guidance to designers on the appropriate FRP-bar configurations and the control of crack width for the FRP-reinforced UHPC deck slab.