： 为探明在不同火灾规模下地下共用结构的整体安全性，进而为类似地下结构防火设计提供参考依据，以义乌商城大道隧道工程为依托，采用有限元软件ANSYS建立火灾下地下共用结构非线性瞬态热-力耦合分析模型，重点研究地下共用结构在不同火灾规模下的位移、应力变化规律以及结构各截面的安全系数。研究结果表明： 1）隧道内火灾规模的扩大会使混凝土力学性能劣化程度愈加严重，在地层荷载作用下受火结构顶板位移急剧增大，而其相邻水平共用结构顶板位移逐渐减小，进而改变共用结构的整体变形形态；且火灾高温作用会使得隧道共用结构发生应力重分布，其应力变化程度随火灾规模的增大而显著增大。2）隧道内大型客车发生火灾时，受火结构对其相邻的水平共用结构应力及安全性有较大影响，而对竖向共用结构影响较小，但可保证共用结构整体安全。

In order to clear the holistic safety of the underground combined structure under different fire scales, and provide reference for the fire protection design of tunnel structures, a nonlinear transient thermalmechanical coupling analysis model for the underground combined structure of Shangcheng Avenue Tunnel in Yiwu under fire is established by using finite element software ANSYS; the variation laws of the displacement and stress of the underground combined structure under different fire scales are studied; and the safety factor of each crosssection of the tunnel structure is analyzed as well. The results show that: （1） The increasing fire scale in the tunnel will deteriorate the mechanical properties of the concrete more seriously, and the displacement of the roof of the fireaffected structure will increase sharply under loading effect; nonetheless, the displacement of the roof of the adjacent horizontal combined structure decreases gradually, which will change the holistic deformation form of the combined structure; the stress redistribution occurs in the underground combined structure under fire, and the degree of changing stress will increase significantly with the increase of the fire scale. （2） When a megabus in the tunnel is ignited, the fireaffected structure has a greater impact on the stress and safety of the adjacent horizontal combined structure, but a smaller impact on the vertical combined structure, which still ensures the holistic safety of the underground combined structure.