单层网壳结构稳定分析中初始几何缺陷最大值的研究

Investigation on maximum value of initial geometric imperfection in stability analysis of single layer reticulated shells

初始几何缺陷的分布模式与大小对单层网壳的稳定性有较大影响。采用随机缺陷模态法,对K8型单层网壳进行了1 200例模型结构的弹塑性荷载-位移全过程分析。综合考虑结构的受力状态、初始几何缺陷对结构稳定的影响程度以及实际施工情况等因素,提出了初始几何缺陷最大值的合理取值。研究表明:随着初始几何缺陷最大值的不断增加,单层网壳结构受力状态由以薄膜内力为主逐渐向以弯曲内力为主转变,当初始几何缺陷最大值增大至跨度的1/300时,结构的受力状态不再以薄膜内力为主;若以轴向应力为主杆件的弯轴应力比统计均值不大于0.25,且其所占有效杆件的百分比统计均值不少于70%时,可认为结构的受力状态是以薄膜内力为主;当缺陷影响系数取0.5时,初始几何缺陷对结构稳定性能的影响显著;初始几何缺陷最大值取跨度的1/500较为合理。

Distribution mode and magnitude of initial geometric imperfection have significant influence on the stability of single layer reticulated shells. By using the random imperfection mode method,1 200 cases of elasto-plastic loaddisplacement overall process for Kiewitt-8 single layer reticulated shells were analyzed. Considering the internal force state of the structure,the influence extent of initial geometric imperfection on the structure and the realistic situation of construction,the reasonable maximum value of initial geometric imperfection is proposed in this paper. The results show that with the increase of maximum value of initial geometric imperfection,the internal force state of single layer reticulated shells changes from internal membrane force to internal bending force gradually. When the maximum value of initial geometric imperfection reaches 1 /300 of the span,the internal force state of the structure is no longer internal membrane force predominantly. If the statistical mean bending-axial stress ratio of the members with the predominance of axial stress is not greater than 0. 25 and the statistical mean percent of the valid members not less than 70%,the internal force state of the structure might be called internal membrane force. When the imperfection influence factor is set to be 0. 5,the influence of initial geometric imperfection on the structural stability is reflected remarkably. A1 /500 of the span could be appropriately taken as the maximum value of initial geometric imperfection.