Reliability analysis of prestressed concrete beams exposed to fire

A procedure for conducting reliability analysis of prestressed concrete beams subjected to a fire load is presented. This involves identifying relevant load combinations, specifying critical load and resistance random variables, and establishing a high-temperature performance model for beam capacity. Based on the procedure, an initial reliability analysis is conducted using currently available data. Significant load random variables are taken to be dead load, sustained live load, and fire temperature. Resistance is in terms of moment capacity, with random variables taken as prestressing steel ultimate strength, concrete compressive strength, placement depth of strands, beam width, and thermal diffusivity. A semi-empirical model is used to estimate beam moment capacity as a function of fire exposure time, which is calibrated to experimental data available in the literature. The effect of various beam parameters were considered, including cover, aggregate type, concrete compressive strength, dead to live load ratio, reinforcement ratio, end restraints, fire exposure, and proportion of end strands to total strands. Using the suggested procedure, reliability was estimated from zero to four hours of fire exposure using Monte Carlo simulation. It was found that reliability decreased nonlinearly as a function of time, while the most significant parameters were concrete cover, load ratio, fire type, end restraints, and proportion of end strands to total strands.