Residual shear behaviour of steel-concrete composite girders after fire exposure: Experimental and numerical study

Steel-concrete composite girders are widely used for their superior mechanical performance. However, research on the shear behaviour of composite girders after fire exposure is limited. This study attempts to reveal the effects of high temperatures and cooling methods on the shear behaviour of composite girders. With heating temperatures (200 degrees C, 400 degrees C and 600 degrees C) and cooling methods (natural cooling and water cooling) as variables, 7 composite girders were designed. First, the composite girders were placed in the fire furnace and heated to simulate fire exposure. Subsequently, the residual shear performance of the cooled composite girders was tested and discussed. The test results show that there is a significant temperature gradient along the height of the girders during heating. High temperatures of no more than 600 degrees C have a more pronounced effect on the properties of concrete than steel, resulting in a progressive deterioration in the synergistic working property of the concrete slab and steel beam as the temperature increases. The deterioration of the shear performance of composite girders with natural cooling is similar to those with water cooling, probably due to the neutralization of the positive effect of water on the hydration reaction of concrete and the negative effect of the rapid reduction in temperature of the structure caused by water cooling. Further, finite element models of the composite girders were developed and thermal-mechanical coupling analysis was performed to simulate the effects of fire exposure. The parametric analysis conducted show that the steel beam web thickness is highly effective in enhancing the residual shear performance of the composite girders after fire, while the effect of the concrete slab width is relatively minor.