空间网格结构抗震薄弱区识别的静力推覆方法

A static pushover method for identifying weak areas of earthquake resistant space frame structures

空间网格结构在强震下出现薄弱区的原因是该区域杆件的地震内力与决定其截面配置的非抗震设计内力差异较大,且该内力差异主要来自于少数模态的贡献。为此,利用非抗震设计和多遇地震验算的最不利内力,提出了一种疑似薄弱区杆件的简便判别方法。基于多遇地震下由振型分解反应谱法计算得到的结构响应,可以确定疑似薄弱区杆件地震内力的主要贡献模态。考虑这些主要贡献模态并参考振型质量参与系数,构造了能够近似反映最不利单向地震响应的综合模态,并基于结构应变能相等的原则确定了罕遇地震水平的等效静力推覆荷载。给出了一种能够计入三向地震动贡献的静力推覆方法,并对一个三心圆柱面双层网壳算例进行了推覆分析。通过与动力弹塑性时程分析结果对比发现,只要在建立推覆荷载时组合模态包括了疑似薄弱区杆件地震内力的主要贡献模态,并且所有组合模态的振型质量参与系数之和大于90%,则该静力推覆方法可以有效识别到该结构在罕遇地震下可能形成的薄弱区。

The occurrence of weak areas in a space frame structure under strong earthquakes is because the internal forces of the members in this area under earthquakes are considerably different from their non-seismic design internal forces that determine the configuration of cross-section, and the internal force difference mainly comes from the contribution of a few modes. Using the most unfavorable internal forces of both non-seismic design and frequently occurred earthquake check, a simple method for judging the suspected members in weak areas is proposed. Based on the structural responses under frequently occurred earthquakes obtained by the mode-superposition response spectrum method, the modes mainly contributing to the seismic internal forces of suspected members in weak areas can also be determined. Considering these main contribution modes and referring to the modal participating mass ratios, an integrated mode that can approximately reflect the most unfavorable unidirectional seismic response is established, and the equivalent static pushover load corresponding to the intensity of rare earthquakes is determined based on the principle of equivalent structural strain energy. A static pushover strategy that includes the contributions of three-dimensional ground motions is suggested, and a pushover analysis is carried out for an illustrative three-centered double-layer reticulated dome. By comparing with the results obtained by the dynamic elasto-plastic time-history analysis, it is revealed that the possible weak areas in the structure under rare earthquakes can be effectively identified using the proposed static pushover method as long as the main contribution modes to the seismic internal forces of the suspected members in weak areas are included in the combination modes and the sum of the modal participating mass ratios of all the combined modes is greater than 90% when constructing the pushover loads.