受火约束钢梁在升温段和降温段行为的理论分析(Ⅱ)

Analysis of Restrained Steel Beams Subjected to Temperature Increasing and Descending Part Ⅱ: Validation and Parametrical Analyses

通过约束钢梁抗火试验结果与笔者提出的理论方法结果的比较,验证了升温段理论分析方法的正确性。在降温段,采用本文方法所得结果与其他理论所得结果也很相近。采用笔者提出的理论方法对约束钢梁进行了参数分析,研究了约束钢梁的轴向约束刚度、转动约束刚度、荷载比、梁的高跨比、钢材屈服、荷载作用类型和截面温度分布等因素对受火约束钢梁在升温段和降温段的影响。研究表明,上述因素,尤其是梁的荷载比、轴向约束刚度和高跨比等对约束钢梁在火灾升温段的行为有很大影响;在降温段,由于梁的收缩受到约束,引起很大的轴向拉力,轴向力的大小除了与梁的荷载比、轴向约束刚度有关外,还与梁所经历的最高温度有关。

The theoretical method for analysing the behavior of restrained steel beams subjected to temperature increasing is validated by experimcntal results. The behavior of the steel beam in cooling phase obtained by the theoritical method presented in this paper is similar to that obtained by previous theoritical methods. The restrained steel beam subjected to temperature increasing and descending is parametically studied by the proposed method. Parameters investigated include the stiffness of the axial restraints, the stiffness of the rotational restraints, load ratio, depth span ratio of the beam, the yield strength of the steel, load type and the distribution in the section. Through the analyses, it is found that all the parame ters mentioned above take important role on the behaviour of the restrained beam with temperature in creasing, especially for the load ratio, the axial stiffness of the restraints at the ends and the depth span ratio of the steel beam. When temperature descends, because the contraction of the beam is restrained, very large tension force will be produced, besides the load ratio and the axial stiffness of the restraints, the parameters effecting the behaviour of the beam also includs the highest temperature the beam undergoing in the fire.