Governing failure criterion of short-span hybrid FRP-UHPC beams subjected to high shear forces

An experimental investigation into the shear performance of a recently developed hybrid section constructed from a glass fibre reinforced polymer (GFRP) hollow box section with an ultra-high performance concrete (UHPC) flange and a bottom sheet made of steel fibre reinforced polymer (SFRP) or carbon fibre reinforced polymer (CFRP) is presented. This section has superior structural properties compared to sections made from conventional materials. Seven specimens were tested by applying a point load 280 mm from one support over a clear span of 1120 mm to induce shear failure. Two main parameters were investigated, namely, the effect of flange dimensions and the type of reinforcement used as the bottom (tension) sheet. All specimens failed similarly, indicating consistent behaviour for shear failure regardless of the changing parameters. Failure involved crack propagation at the corners of the GRFP box section followed by cracking of UHPC flange. Traditional calculations, based on the elastic analysis, of the shear stresses at the failure point are presented showing that high shear stresses are not the only cause of the mode of failure observed. The cause of failure is interpreted using a simple finite element analysis. Given the cause of failure, special consideration should be given to the design of the fibre orientation at the corner regions of such box sections.