مقاومت فشاری محوری ستون های فولادی S460 جوشکاری شده در دمای بالا Axial compressive strength of welded S460 steel columns at elevated temperatures

1. Introduction The use of high strength steel (HSS) with nominal yield strength over 460 MPa in structural construction brings about considerable advantages over mild steel. By using HSS, lighter structural members with smaller cross-section sizes can be adopted, resulting in the significant material savings and easier handling during construction. Consequently, the transportation and construction costs can be reduced. Besides, the lesser consumption of steel materials also generates higher environmental efficiency. In order to carry out accurate design of HSS structures, extensive research studies have been conducted to determine the behaviour of cold-formed and welded HSS columns under compression at room temperature. The local buckling behaviour and strength of HSS stub columns were investigated in experiments and numerical modelling [1–6] and revised slenderness limits for crosssection classification were proposed [7]. The global buckling resistance of HSS columns was also investigated [4,5,8–11] and suitable buckling curves for the design of HSS columns were also proposed [8–10,12]. However, although great progress in developing room temperature design guidance for HSS columns has been made, the performance of HSS columns under elevated temperature conditions has received much less attention and needs to be thoroughly investigated for designing the structures for the possibility of fire exposure. The behaviour of BISALLOY 80 high strength steel (with the nominal yield strength of 690 MPa) columns with box and I- sections at elevated temperatures was investigated numerically by Chen and Young [13]. A parametric analysis was performed to determine the temperature effect on the strength of both stub columns with various cross-section slenderness and long columns with different slenderness ratios. The suitability of specifications in European, American and Australian standards and direct strength method [17] for BISALLOY 80 high strength steel columns at elevated temperatures was assessed by comparing the results of the parametric study with those of the column strength predicted based on the standards with the substitution of material properties at elevated temperatures. It was found that European and American specifications and direct strength method could be used to conservatively predict the strength of BISALLOY 80 high strength steel columns at elevated temperatures. Wang and co-workers [19] conducted experiments to investigate the axial compressive strength of welded Q460 steel columns at only two temperatures of 450 °C and 650 °C and the column specimens with two cross-section sizes were tested. It was found that the axial compressive strength of the columns at 650 °C was significantly lower than that of the columns at 450 °C due to the deterioration of material strength and stiffness with increasing temperatures. However, no systematic study has been conducted to investigate the strength of 460 MPa steel columns at varying elevated temperatures that the structures may experience under fire condition. In this study, the axial compressive strength of welded S460 steel columns with box and H- sections at elevated temperatures was investigated using finite element analysis. Firstly, a stress-strain model for S460 steel at elevated temperatures was proposed based on the experimental results obtained by Qiang and the co-workers [20] for structural design and analysis.