Nonlinear behavior and bearing capacity of steel-concrete composite structures in fire conditions by a plastic hinge-based approach

This paper aims to evaluate the nonlinear behavior and bearing capacity of steel-concrete composite beams, columns and frames in fire situation. The steel and concrete materials composing structural members and systems have their bearing capacity compromised when exposed to high temperature conditions, since their physical and resistance characteristics deteriorate as the temperature rise. Thus, the two computational modules, CS-ASA/FA (Computational System for Advanced Structural Analysis/Fire Analysis) and CS-ASA/FSA (Fire Structural Analysis) are modified and adapted for the thermal analysis and the second-order inelastic analysis of composite structures under elevated temperatures. The first module calculates the temperature field in any composite crosssection, and any face loaded thermically, from which also the materials properties degradation exposed to fire can be obtained. The second computational module performs the second-order inelastic analysis of composite structures in fire situation by the Strain Compatibility Method (SCM) and Refined Plastic Hinge Method (RPHM) coupling. In the second-order inelastic analysis context via finite element method (FEM), a co-rotational large displacements element formulation is used to follow the composite structural members and frames movement. The proposed advanced numerical methodology for composite structures in fire conditions is evaluated and tested using many experimental and numerical results available in the literature showing very good agreement.