This paper investigates the response of tall setback irregular steel moment resisting structures under traveling fires. A seven‐story steel regular structure (RS) is first designed for gravity and seismic loads and then it is fireproofed for a fire resistance rating (FRR) of 120 min based on the ISO834 fire. Some architectural changes are then imposed on the RS to make it a setback irregular structure (SBS). Based on the traveling fire methodology, both structures are then subjected to fire curves ranging from 1% to 100% for the fire load density (q_f) of 570 MJ/m². As in the SBS, the distribution of gravity loads is not uniform; the structural fire analyses are performed twice: when the fires start from left to right and then vice versa. The results show the FRR of the RS is minimized under the fire size of 22% with the collapse time of 87.0 min. In the SBS, when the fires start from left to right and then from right to left, the FRR is minimized under the fire size of 20% with the collapse times of 75.0 and 79.0 min, respectively. This shows that the SBS is more vulnerable toward traveling fires than the RS. In order to monitor the role of q_f in the FRRs of the structures, q_f is then reduced, and the required analyses are repeated. This process continues to where no collapse is observed under all the fire sizes. The results indicate that the RS would remain stable if the q_f is decreased to 480 MJ/m², implying that a 16% increase should be considered to the required FRR. As for the SBS, the q_f should be decreased to 440 MJ/m² to make it stable, meaning that a 25% increase should be considered to the required FRR.

中文翻译：

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火灾下不规则钢结构的脆弱性评估

本文研究了行进火势下高倒退不规则钢抗弯结构的响应。首先设计一种七层钢常规结构（RS），以承受重力和地震载荷，然后根据ISO834防火标准对其进行防火，耐火等级（FRR）为120分钟。然后，对RS进行一些体系结构更改，以使其成为挫折不规则结构（SBS）。根据行进火场方法，对于570 MJ / m ²的火场密度（q _f），两个结构都将经受从1％到100％的着火曲线。与SBS中一样，重力载荷的分布也不均匀。结构火灾分析执行了两次：火灾从左向右开始，然后反之亦然。结果表明，在火势为22％，崩溃时间为87.0分钟的情况下，RS的FRR最小。在SBS中，当火灾从左向右开始然后从右向左开始时，在20％的火灾大小下，FRR最小，崩溃时间分别为75.0和79.0分钟。这表明，SBS比RS更容易受到行进火灾的影响。为了监视q _f在结构的FRR中的作用，q _f然后减少，然后重复所需的分析。这个过程一直持续到在所有火势下都没有观察到坍塌的地方。结果表明，如果q _f降至480 MJ / m ²，RS将保持稳定，这意味着应将所需的FRR增加16％。对于SBS，应将q _f降低至440 MJ / m ²以使其稳定，这意味着应考虑将所需的FRR增加25％。