杆件失效路径对网架结构抗火性能的影响

在正放四角锥网架结构抗火性能研究基础上,进一步分析两向正交正放网架、正放抽空四角锥网架和斜放四角锥网架在大空间建筑火灾中的热力耦合反应.基于有限元程序ANSYS建立网架结构上弦压杆应力比一致的结构分析模型,按温度增量加载的方法对网架结构热力耦合非线性反应进行了分析.结果表明,在大空间建筑火灾非均匀温度场中网架结构具有不同的杆件失效路径,正放四角锥网架、正放抽空四角锥网架和斜放四角锥网架在各自的杆件失效路径下临界温度趋于一致;网架结构在火灾中产生适度数量的杆件破坏,可更大程度地释放附加温度应力,表现出结构具有较高的抗火承载力和临界温度;两向正交正放网架的水平支撑桁架体系的抗火承载力对结构的整体抗火承载力有较大影响.按上弦杆具有相同应力比的结构模型,分析得到的失效杆件是影响结构抗火承载力的关键杆件.上述结论可为进一步研究网架结构抗火设计方法提供理论依据.

Influence of element failure route on fire-resistance of space trusses

Based on fire-resistance analysis of regular pyramidic space trusses,the thermo-mechanical coupling effects of two-way orthogonal space trusses,diagonal square pyramidic space trusses and orthogonal extracted pyramidic space trusses was analyzed.With the help of finite element software ANSYS,a series of grid structure models with the same stress ratios of upper chord members was developed for analysis of the globe structural thermo-mechanical coupling effects caused by fire,using temperature increment method.The results from finite element method show that regular pyramidic grid structures,diagonal square pyramidic grid structures and orthogonal extracted pytamidic space trusses have the same critical temperature with different element failure routes.A suitable number of element failure can release thermal stress greatly and improve structural fire-resistance capacity and critical temperature.The critical temperature of two-way orthogonal space trusses is dependent on that of its horizontal braced truss.The elements in failure route are key members which determine structural fire-resistance.These conclusions can be employed by further research on structural fire resistant design method.