Effect of cracking and residual deformation on behavior of concrete beams with different scales under fire exposure

Abstract This paper presents results from fire tests on reinforced concrete beams (RC) with different levels of pre-damage, to evaluate the effect of pre-cracking and residual deformations on the behavior of concrete beams under fire exposure. Two groups of RC beams with proportional geometric dimensions (1:2) and same reinforcement ratio, were tested under fire exposure. The pre-damage (cracking and residual deflection) was induced by applying different levels of static loading on the beams prior to undertaking fire tests. The progression of cracking patterns and deflection prior to and during fire tests were recorded. Data is utilized to compare the thermal field, structural response and fire resistance of beams with and without pre-damage. Results from these tests show that the width (less than 2 mm), number and length of cracks, formed prior to the fire exposure, only have a limited effect on the temperature development in concrete layers closer to the fire exposed surface, but no significant influence on the temperature rise in the internal layers of concrete, including at the location of longitudinal reinforcement in the beam. When determining the fire resistance of a pre-damaged beams, including (or excluding) the residual deflection, formed prior to fire exposure, in the total deflection has no remarkable effect on the fire resistance values. And slight pre-damage has no significant effect on the fire resistance of beams, but major pre-damage (such as almost reaching the yielding of reinforcement) influences the fire resistance, especially in case of larger-scaled beams. The more predominant effect of pre-damage level on the fire resistance in larger-scaled beams is due to the influence of size effects.