Numerical investigation on post–fire resistance of cold–formed Q960 ultra high strength steel channel section stub columns

Abstract

Numerical analyses on the residual resistant performance of cold–formed Q960 ultra high strength steel (UHSS) channel section stub columns after fire exposure were reported. The proposed numerical modelling method was validated by the existing experimental results of the cold–formed EN 1.4420 austenitic stainless steel, S690 high strength steel (HSS) and S960 UHSS channel section stub columns at room temperature, and the hot-rolled EN 1.4301 austenitic stainless steel channel section stub columns after exposure to fire, where the ultimate resistance, load–end shortening curve and failure mode were considered. The satisfactory comparisons demonstrate the appropriateness of the proposed numerical modelling methodology for the Q960 UHSS channel section stub columns after fire exposure. A parametric study considering different geometric dimensions and exposure temperatures was conducted, where a total of 410 numerical models were included. The geometric dimensions of cold–formed Q960 UHSS channel section stub columns changed the effects of exposure temperature on the load–end shortening curve. For the conditions after exposure temperature less than 600 °C, the slenderness limit of Class 3 in European code could be used for cold–formed Q960 UHSS channel section stub columns. When the exposure temperatures were at 700, 800 and 900 °C, the slenderness limit of Class 3 became unsuitable. The accuracy of design approaches in EN 1993–1-12, AISI S100, AS/NZS 4600 and direct strength method (DSM) was assessed. When the exposure temperatures were at 800 and 900 °C, there were noticeable differences between the numerical results and results obtained from the abovementioned design approaches. The modification methods considering effects of exposure temperature and geometric dimensions were proposed for the EN 1993–1-12 design approach to predict ultimate resistance of the cold–formed Q960 UHSS channel section stub columns after different exposure temperatures.