Finite element implementation for the analysis of 3D steel and composite frames subjected to fire

This paper presents a finite element formulation for the numerical analysis of three-dimensional framed steel, reinforced concrete or composite steel and concrete structures subjected to fire. Several specialized and commercial programs may be used for the analysis of structures in fire condition. Within this context, the purpose of this work is to present the steps taken to extend a previously developed static analysis procedure with beam elements in order to cope with the thermal and structural analysis of structures under fire action. Physical nonlinearity and material property degradation considering the temperature distribution are taken into account at the cross section level, which is divided into quadrilateral or triangular finite elements. Thermal strains are considered through the effective strain concept, and the resulting nonlinear system of equations is solved by the Newton-Raphson scheme. The accuracy and capability of the formulation to simulate the behavior of framed structures under fire action are assessed through comparison with various numerical and experimental results.