临时支撑卸载安全性是弦支穹顶结构等半刚性结构施工的关键因素之一。基于此背景，本文针对标准弦支穹顶结构提出了卸载冲击荷载下结构的失效判别准则，采用该判别准则，结合ANSYS有限元软件针对临时支撑不同卸载速率对结构动力稳定性能的影响进行分析，研究发现采用直接卸载时，存在一定安全风险，且临时支撑卸载不当可能引起结构失效；提出了不利速率条件下结构失效模式及相应的预警参数；对某大跨度弦支穹顶结构的卸载失效模式和机理进行了研究，验证了本文所提方法可行、有效。

Unloading supporting system is important for semirigid structure, such as suspen-dome, during construction. Thus a failure criterion is presented for standard suspen-domes under unloading impact load. Using the criterion, analysis on the effect of unloading rate on the structure dynamic stability is developed adopting the Ansys software. The results that using direct unloading will be unsafe at some extent, improper unloading can cause structure failure are drawn. And further the structure failure mode and corresponding early warning system are obtained for unloading impact. Research for unloading failure mode and failure mechanism of a project case is presented, which verified the method obtained in the paper advisable and effective.