Experimental investigation of size effects on BFRP-RC beams under combined bending-shear-torsion loading

This study investigated the influence of the member size and torsion-bending ratio on the mechanical property and size effect of BFRP-RC beams under combined torsion-bending-shear loadings. Fifteen BFRP-RC beams with varying torsion-bending ratios and member sizes were tested. The test results show that the specimens' torsional and shear performance can be affected by the torsion-bending ratio. The presence of shear would alter the beams' failure mode and reduce the beams' torsional carrying capacity, ductility, and deformation capacity. This effect becomes more pronounced as the shear ratio increases. Under the combined loadings, the strength, ductility, and deformation capacity of BFRP-RC beams exhibit remarkable size effects. As the beam height enlarges from 300 mm to 900 mm, the torsional and shear strengths can decrease by up to 39.80 % and 42.12 %, respectively. As the torsion-bending ratio increases, the influence of size on torsional and shear strength first strengthens and then weekends, and the critical torsion-bending ratio is 0.6. Furthermore, the rationality of the current design codes was remarked based on the experimental results. The proposed size effect model for Basalt Fiber Reinforced Polymer Bars Reinforced Concrete (BFRP-RC) beams under combined loading was validated to predict their bearing capacities accurately.