Three-dimensional analysis of reinforced concrete beam-column structures in fire

Abstract

In this paper a robust nonlinear finite-element procedure is developed for three-dimensional modeling of reinforced concrete beam-column structures in fire conditions. Because of the changes in material properties and the large deflections experienced in fire, both geometric and material nonlinearities are taken into account in this formulation. The cross section of the beam column is divided into a matrix of segments and each segment may have different material, temperature, and mechanical properties. The more complicated aspects of structural behavior in fire conditions, such as thermal expansion, transient state strains in the concrete, cracking or crushing of concrete, yielding of steel, and change in material properties with temperature are modeled. A void segment is developed to effectively model the effect of concrete spalling on the fire resistance of concrete beam-column members. The model developed can be used to quantify the residual strength of spalled reinforced concrete beam-column structures in fire. A series of comprehensive validations have been conducted to validate the model. From this research, it can be concluded that the influence of transient state strains of concrete on the deflection of structures can be very significant. However, there is very little effect on the failure time of a simple structural member. The impact of concrete spalling on both the thermal and structural behaviors of reinforced concrete members is very significant. It is vitally important to consider the prospect of concrete spalling in fire safety design for reinforced concrete buildings.