Study on the shear behaviour of steel-concrete composite beams after elevated temperature and water cooling

The study of the mechanical behaviour of steel-concrete composite beams under fire is of great importance. However, little attention has been paid to the effect of elevated temperatures on the shear performance of composite beams. This study innovatively investigates the shear behaviour of steel-normal concrete (NC) composite beams and steel-engineered cementitious composite (ECC) composite beams after elevated temperatures and water cooling. The experimental results show that the degradation of the mechanical properties of concrete was more severe than steel after experiencing 200 celcius and 400 celcius. This deteriorates the synergistic working properties of the concrete slab and steel beam, and the shear strength of steel beam was not fully utilised. PVA fibres have completely melted under 400 celcius, and the shear performance of steel-ECC composite beam, particularly the ductility and energy absorption, was found to be significantly reduced. The reductions in the shear capacity, ductility, energy absorption, and initial stiffness after 400 celcius were 12.6%, 23.8%, 31.3%, and 10.2% for the steel-NC composite beam respectively, and 25.7%, 52.8%, 64.3%, and 30.2% for the steel-ECC composite beam respectively. Furthermore, the prediction equation for the residual shear capacity of the composite beams after elevated temperatures and water cooling was established and validated.