Stiffness assumptions affect even a simple incremental analysis and moreover a buckling or 3D elasto-plastic analysis. The Trial Stiffness Selection (TSS) method, that was proposed by the authors and enables a large deformation elasto-plastic analysis of a large 3D frame using stress-strain curves, is newly extended to analyze high temperature collapse of a steel frame. Using the proposed TSS-Thermal (TSST) method, collapse of a tube structure under elevated temperature is analyzed successfully. In thc case with a wide hole on the tube, columns show plasticity in the early stage beside the hole and redistribute their axial forces.
