A test programme looking into the residual mechanical properties of fire exposed high strength steels (HSS) has been presented in this study. Accurate predictions of the residual mechanical properties of fire exposed structures are necessary to develop a proper strategy for their restoration. A test programme was conducted to investigate the post-fire residual material properties of thermomechanical control processed cold-formed HSS tubular members. The nominal yield strengths of tubular members were 900 and 960 MPa. The tubular members investigated in this study were made up of square, rectangular and circular hollow sections. The tubular members were heated inside a gas furnace, where the fire exposure generally followed the heating part of the ISO-834 standard fire [1] curve. The tubular members were exposed to 4 fire exposure temperatures, i.e. 300°C, 550°C, 750°C and 900°C, followed by their natural air-cooling inside the furnace. Subsequently, at ambient temperature, a total of 80 post-fire coupons was extracted from these ISO-834 standard fire exposed tubular members. The post-fire coupons were extracted from the flat, corner and curved regions of the fire exposed tubular members. The post-fire material properties and their respective residual factors were determined using the static stress–strain curves, which were obtained from their corresponding test stress–strain curves. New prediction equations are proposed for the post-fire residual material properties using the post-fire residual factors obtained in this test programme as well as available data in the literature for steel grades more than or equal to S690. It should be noted that two sets of prediction equations are proposed in this study, first, for the flat region, and second, for the corner and curved regions. The proposed prediction equations for the post-fire residual material properties of the flat region are valid for both hot-rolled and cold-formed HSS with nominal yield strengths ranged from 690 to 1070 MPa. Whereas, the proposed prediction equations for the post-fire residual material properties of the corner and curved regions are valid for cold-formed HSS with yield strengths ranged from 900 to 1200 MPa.

这项研究提出了一个测试程序，旨在研究暴露于火中的高强度钢（HSS）的残余机械性能。准确预测火灾暴露结构的残余机械性能对于制定适当的修复策略十分必要。进行了测试程序，以研究热机械控制加工的冷成型HSS管状构件在燃烧后的残留材料性能。管状构件的标称屈服强度为900和960 MPa。本研究中研究的管状构件由正方形，矩形和圆形空心部分组成。管状构件在煤气炉内加热，其着火通常遵循ISO-834标准着火[1]曲线的加热部分。使管状构件暴露于4种火暴露温度，即 300°C，550°C，750°C和900°C，然后在炉内进行自然风冷。随后，在环境温度下，从这些ISO-834标准受火暴露的管状构件中提取出总共80张火后试样。火灾后的试样从着火的管状构件的平坦，拐角和弯曲区域中提取。燃烧后的材料特性及其各自的残余因子是使用静态应力-应变曲线确定的，该曲线是从其相应的测试应力-应变曲线获得的。使用该测试程序中获得的燃烧后残留因子以及大于或等于S690的钢种的文献中的可用数据，提出了燃烧后残留材料性能的新预测方程式。应该注意的是，在这项研究中提出了两组预测方程，第一组用于平坦区域，第二组用于拐角和弯曲区域。所建议的扁平区域火后残余材料特性的预测方程式对标称屈服强度范围为690至1070 MPa的热轧和冷弯高速钢均有效。鉴于此，针对拐角和弯曲区域的火后残余材料特性所提出的预测方程式对于屈服强度范围为900到1200 MPa的冷弯高速钢是有效的。所建议的扁平区域火后残余材料特性的预测方程式对标称屈服强度范围为690至1070 MPa的热轧和冷弯高速钢均有效。鉴于此，针对拐角和弯曲区域的火后残余材料特性所提出的预测方程式对于屈服强度范围为900到1200 MPa的冷弯高速钢是有效的。所建议的扁平区域火后残余材料特性的预测方程式对标称屈服强度范围为690至1070 MPa的热轧和冷弯高速钢均有效。鉴于此，针对拐角和弯曲区域的火后残余材料特性所提出的预测方程式对于屈服强度范围为900到1200 MPa的冷弯高速钢是有效的。