This study numerically examines the changes in dynamic properties of fire-damaged steel trusses made of square hollow sections subjected to uniform and non-uniform heating scenarios. After verifying the numerical models at both ambient and elevated temperatures, a vast number of the simulations were analysed using non-linear finite element software to evaluate the effects of fire scenarios, truss types, and fire-damaged levels on the fire dynamic characteristics of square hollow section Warren, Howe, and Pratt trusses. The results indicated that the natural frequency of steel trusses significantly decreased as the fire-damaged level increased. In the case of local fire, the natural frequencies of the trusses began to drop suddenly at temperatures above 550 °C. Whereas the drop in the natural frequency of the uniformly heated trusses started at even much lower temperature levels. Moreover, the decrease in the natural fundamental frequencies of the uniformly heated trusses was lower than the reduction rate of the modulus of elasticity at high temperatures due to the large non-linear deformations. Since the modification of the stiffness of the truss by simply the reduction factor of the elastic modulus of the steel may be inappropriate to calculate the fundamental frequency of the trusses in the local and global fires, a new method was introduced to calculate the fundamental frequency value of the steel trusses in the fire.

本研究以数值方式研究了由方形空心型材制成的火灾损坏钢桁架在均匀和非均匀加热情况下动态性能的变化。在验证了环境温度和高温下的数值模型后，使用非线性有限元软件对大量模拟进行了分析，以评估火灾场景、桁架类型和火灾损坏程度对方形火灾动态特性的影响空心截面沃伦、豪和普拉特桁架。结果表明，随着火灾损坏程度的增加，钢桁架的固有频率显着降低。在局部火灾的情况下，桁架的固有频率在温度高于 550 °C 时开始突然下降。而均匀加热桁架的固有频率在更低的温度水平下就开始下降。此外，由于较大的非线性变形，均匀加热桁架的固有基频的降低率低于高温下弹性模量的降低率。由于简单地通过钢材弹性模量的折减系数来修改桁架刚度可能不适合计算局部和整体火灾中桁架的基频，因此引入了一种新的方法来计算基频值钢桁架在火灾中的情况。由于较大的非线性变形，均匀加热桁架的固有基频的降低率低于高温下弹性模量的降低率。由于简单地通过钢材弹性模量的折减系数来修改桁架刚度可能不适合计算局部和整体火灾中桁架的基频，因此引入了一种新的方法来计算基频值钢桁架在火灾中的情况。由于较大的非线性变形，均匀加热桁架的固有基频的降低率低于高温下弹性模量的降低率。由于简单地通过钢材弹性模量的折减系数来修改桁架刚度可能不适合计算局部和整体火灾中桁架的基频，因此引入了一种新的方法来计算基频值钢桁架在火灾中的情况。