Post-fire behavior of lightweight concrete corbels

Abstract

Corbels are small cantilevers used extensively in precast structures to transfer concentrated loads to columns. Many precast structures are made of lightweight concrete (LWC), and in case they suffer a fire event, investigating the residual strength of their corbels becomes essential. This study aims to examine the performance of LWC corbels exposed to elevated temperatures, present a calculation methodology for estimating their residual capacity, and assess, for the first time, the difference between the behavior of LWC and normal-weight concrete (NWC) corbels. Twelve full-scale reinforced concrete corbels were fabricated with LWC or NWC and different shear span-to-depth ratios and reinforcement details. The specimens were subjected to loading until failure at ambient temperature, either without heat exposure or after exposure to temperatures exceeding 750 °C. Experiencing elevated temperatures reduced the strength of LWC corbels by 44–54%, compared with 33–50% for NWC specimens; though generally similar residual behaviors were observed for LWC and NWC specimens. The strut-and-tie method (STM) provided good estimates of the strength of LWC and NWC specimens if the residual compressive strength of concrete based on the average temperature between the core and the surface of the specimens is used in calculations. The ratio of calculated capacity to measured strength ranged between 0.73 and 1.02 for LWC and between 0.66 and 0.86 for NWC specimens.