Development of beam elements for nonlinear analysis of reinforced concrete frames subjected to fire

A beam element was developed for nonlinear analysis of three-dimensional reinforced concrete frames subjected to fire. The formulation considers three critical aspects: the coupling between axial and bending deformations, thermal elongation, and the slenderness effect caused by fire. The formulation incorporates a Jacobian matrix between the internal forces and strain parameters to enhance the computational efficiency. Nonlinear analyses of the structures were conducted at ambient and elevated temperatures to verify the proposed beam elements. To statistically validate the accuracy, we analyzed 82 columns exposed to ambient temperature and 74 columns exposed to elevated temperatures, and compared them with the experimental results. The applicability of the proposed analysis method was demonstrated through the analysis of three-dimensional reinforced concrete frames. The beam element can be used for the performance-based fire design of reinforced concrete building structures.