考虑初始几何缺陷的网壳结构整体稳定性可靠度分析

网壳结构的设计由重力荷载和初始几何缺陷共同作用下的整体稳定性控制,而结构的初始几何缺陷形状和最大值是未知的。采用联立自回归模型分别对球面网壳和柱面网壳结构的初始几何缺陷进行建模,研究空间相关初始几何缺陷对结构整体稳定极限承载力概率分布和可靠度的影响。评估杨氏模量对不同荷载工况作用下极限承载力概率分布和可靠度的影响。在永久荷载与雪荷载作用下,杨氏模量的影响可以忽略不计;如果各节点初始几何缺陷标准差的最大值等于1/2或1/3规范推荐的初始几何缺陷最大值,按规范中安全系数满足2的规定进行设计,结构的失效概率约小于6.5×10^-5;若安全系数取1.5,结构失效概率约小于5.1×10^-4。考虑永久荷载与活荷载的组合时,如果各节点初始几何缺陷标准差的最大值等于1/2或1/3规范推荐的初始几何缺陷最大值,安全系数取2时,网壳结构的失效概率均可忽略不计;若安全系数取1.5,球面网壳及柱面网壳的失效概率分别小于10^-7和10^-6。即若达到规范采用的可靠度,规范中的安全系数也许可降低至1.5且可针对不同地区确定不同安全...

Reliability analysis of stability of latticed shell structure considering initial geometric imperfections

The design of latticed shell is governed by the global instability requirements for gravity load and specified shape and amplitude of maximum initial geometric imperfection (IGI). The assigned shape and maximum IGI is unknown. In the present study, IGI is modelled using the simultaneous autoregressive model. By using this model, the effect of the spatially correlated IGI on the probability distribution of the load capacity for global instability and the reliability of spherical and cylindrical latticed shell is assessed. Furthermore, the effect of Young’s modulus on the probability distribution of the load capacity and the reliability under different load combinations are assessed. Under permanent load and snow load, the effect of Young’s modulus can be ignored. A critical load factor of 2 implemented in the code leads to a failure probability less than about 6.5×10-5if the specified maximum IGI defined in the code equals about two to three times the standard deviation of IGI. This failure probability becomes less than about 5.1×10-4 if a critical load factor of 1.5 is used. Under permanent load and live load, a critical load factor of 2 leads to negligible failure probabilities for two latticed shells if the specified maximum IGI equals about two to three times the standard deviation of IGI. This failure probability becomes less than about 10-7 for spherical latticed shell and 10-6 for cylindrical latticed shell if a critical load factor of 1.5 is used. It is suggested that the critical load factor may be reduced to 1.5 while achieving target reliability index often adopted for design code, and different critical load factors can be determined for different regions.