Structural response of prestressed concrete members subjected to elevated temperatures

A numerical procedure is developed for the nonlinear analysis of the structural response of prestressed concrete members subjected to fire. The fire environment is simulated by the time-temperature relationship of the standard fire test (SFT). The procedure computes temperature distributions, mid-span deflection and moment capacity of a member supporting its design service loads throughout the simulated fire exposure period.;The formulation of the numerical model and the solution of the equilibrium equations is based on the displacement finite element method. The member cross section is idealized into triangular elements for temperature distribution analysis and for evaluation of variation in material properties within the section. Beam elements are used to model the member for both deflection and moment capacity analysis. The transient heat transfer mechanisms of the SFT is modeled by dividing the time scale into discrete number of time steps. At each time step equilibrium equations are set and solved iteratively for temperature distribution and structural response. Incremental deflections within a time step are added cumulatively to determine the total deflection at the end of each time step.;A series of numerical analyses of prestressed concrete beams and slabs, and the evaluation of the influences of temperature-dependent properties of concrete and steel on temperature distribution, deflection and moment capacity is presented. Numerical results show good agreement with corresponding test results. Temperature distribution is more sensitive to thermal capacity properties for normal weight concretes and to thermal conductivity properties for lightweight concretes. Deflection is mostly influenced by the effects of temperature on the relaxation properties of prestressing steel. Thermal properties of concrete influence both the deflection and moment capacity.;Graphs for predicting fire endurance of prestressed concrete beams exposed to fire have been developed both for normal and lightweight concretes.