Structural Performance and Design of HSS Welded H-Section Members under Combined Compression and Major-Axis Bending at High Temperatures

This research includes an experimental and numerical investigation into the fire resistance of high-strength steel (HSS) welded H-section long columns under combined loading. Major-axis eccentric compression tests at the temperature of 600°C were carried out on HSS welded H-section long column specimens. The experimental investigation comprised high-temperature tensile coupon tests, measurement of geometric imperfection, and steady-state tests. After the development and validation of the results of the steady-state tests, the finite element model (FEM) was applied in a parametric investigation. Finally, both experimental and numerical data were utilized to assess the applicability of the relevant design provisions for the ultimate bearing capacity of Q460, Q690, and Q960 HSS long columns under major-axis combined loading at 600°C, as provided in European and American fire design standards, as well as the Chinese room temperature specification and the direct strength method (DSM). The results of these assessments revealed that (1) both the European and American fire design standards offered conservative resistance predictions for HSS welded H-section columns failing by flexural buckling about the major principal axis, while the design buckling curve in European specification results in consistent flexural buckling resistance predictions; and (2) the codified ambient temperature design buckling curves in Chinese specifications exhibited conservative interactive buckling resistance predictions, yet the DSM showed overpredicted resistances.