Behaviour of hybrid FRP–UHPC beams in flexure under fatigue loading

The fatigue behaviour of innovative hybrid FRP–UHPC beams under flexural loading is investigated in this paper. The beams were made up of a pultruded GFRP hollow box section beam with a cast-in-place UHPC layer on top and either a CFRP or SFRP sheet bonded along the bottom. Four hybrid beams were tested under variable amplitude loading, to determine the effect of cyclic loading on flexural strength and stiffness. Analysis also included the development of a modified S–N curve and evaluation of fatigue damage using the Palmgren–Miner rule. It was found that insignificant loss in strength and stiffness occurred for all beams, where the fatigue damage estimated using the Palmgren–Miner rule overestimated the fatigue life. It was postulated, by comparison, that the hybrid beams reinforced with CFRP sheets may perform better under fatigue loading than the beams reinforced with SFRP sheets.