RESPONSE OF SIMPLY SUPPORTED PRELOADED RC BEAMS EXPOSED TO FIRE

Abstract

Fires leave behind its high impact on a structure. During a fire event different parts of a - structure may get exposed to different level of temperatures which may cause partial damage or total collapse of the structure. The level of damage depends upon many factors including the pre load level. Hence, residual moment capacity of a structure is a function of Preload level. For undertaking any residual capacity evaluation it is a desirable input to know the Preload level. This study brings out the effect of various Preload levels on the Residual Moment Capacity and temperature profile inside RC beams. Preload Level influences the thermal profile inside RC beams to some extent. With increasing load level and consequent cracking, of the order of I O m in the outer layers, the thermal profile reflects a decreased temperature profile inside various layers of concrete. But with the propagation and widening of the cracks the temperature increases inside the concrete layers leading to temperature dependent • strength reduction of concrete and reinforcing steel. Increasing load levels have adverse effect on the moment capacity of a fire damaged RC flexural element after cooling to ambient temperature. A method for determining the residual moment capacity specifically for short duration fires of less than 1 hr has also been proposed and validated with the experimental results obtained from testing of full scale beams (length-4m, depth-0.4m, width-0.23m). The moment capacity evaluation by using strength reduction model as given in Eurocode and strength reduction model of steel as proposed by Tao et al gives the best results.