Experimental and numerical study on fire-induced collapse of double-span steel portal frames

Abstract

This paper introduces experimental and numerical investigations on the fire-induced collapse behavior of double-span steel portal frames. A natural fire test was conducted on a 16 m × 6 m portal frame, and a localized collapse occurred. Thermal and displacement responses of the test frame were measured and analyzed. It was found that the steel members inside the fire compartment experienced similar temperature-time curves, which reached 1000 °C in 15 min. The heated column experienced upward expansion and downward contraction, while the side columns were pushed outside and pulled inside during the fire test. The measuring accuracy and practicability of the thermocouple, microwave radar, inclinometer, and linear variable differential transformer (LDVT) in real fire measurements were compared and evaluated. Numerical models were established in FDS and ABAQUS to simulate the thermal and structural response of the test frame and validated against experimental results, respectively. Parametric analysis was conducted on the validated numerical models with various combinations of heating conditions, heating rates, load ratios, and base stiffness. The collapse temperature of the burning frame was 1.2 and 1.1 times the temperature when the displacements of the heated side column reached their peak values along the span and height directions, respectively.