Experiment and Analysis on the Mechanical Behaviour of PC Simply-Supported Slabs Subjected to Fire

Abstract

Experiments on the fire resistance of 9 unbonded and 1 bonded prestressed concrete (PC) simply-supported slabs are completed. Calculation formula of the stress in the unbonded prestressing steel wires in PC simply-supported slabs subjected to fire is obtained based on the experimental results. Dividing the section of the slab into strips along its depth according to the distribution of temperature field, on the basis of invariable width of the slab in the surface exposed to fire, the transformed section of the slab subjected to fire can be obtained by multiplying the width of each strip by the elasticity modulus ratio of the strip concerned and the extreme strip in the surface exposed to fire. The stress in concrete and curvature in the researched section caused by load can be obtained based on equilibrium equations of force and moment on transformed section. Then, the methods for calculating concrete thermal strain, transient strain and creep at elevated temperature were introduced, and total strain of a point in the concerned section and total curvature caused by load and temperature can be calculated considering time-dependent effect. After the total curvature of the mid-span section was calculated, the actual stiffness of the critical section in the mid-span can be determined, moreover, the mid-span deflection of the PC slab can be calculated by the virtual displacement principle. The practical calculation formulas for the mid-span deflection of PC simply-supported slabs subjected to fire is presented considering the influences of the deflection of slabs at the ambient temperature, ratio of concrete cover to depth of slabs, load level, combined reinforcement index and span.