直接分析法在抗震设计中的运用

Application of direct analysis method in performance-based seismic design

直接分析法因在分析过程中考虑二阶效应、结构整体和构件初始缺陷、材料弹塑性、节点连接刚性等对结构响应有影响的因素,使得分析和设计不再分离,从而在本质上解决了传统计算长度法在结构稳定性设计中的问题。该方法在众多规范中受到推崇,包括最新的钢结构标准(GB 50017—2017)。直接分析法生而具有的开放性,也使得它可以应用在结构分析和设计的各个阶段,实现各种性能目标。为满足直接分析法的要求,该文推导了基于力法的可直接考虑构件几何初始缺陷和残余应力的高性能梁柱单元。该单元还可考虑构件的弹塑性发展,具有很高的精度,一构件一单元即可适用于常见结构。该文探讨了直接分析法在抗震设计中的运用,提出基本分析框架,并指出分析中应注意的问题。

Direct analysis method（DAM） considers the major factors significantly affecting the structural behaviors, such as second-order effects, global frame imperfection and member imperfection, material yielding and joint finite stiffness. This method integrates the design requirements in the process of analysis and as a result, the effective length assumption is no longer needed. DAM is highly recommended in many modern design codes including the latest Chinese code GB50017-2017. DAM is based on the nonlinear finite element analysis and therefore it can be extended to performance-based seismic design. To meet the codified requirements of DAM, a flexibility-based element considering the member initial bowing, residual stress and material yielding is proposed in this paper for seismic design. This new element shows high accuracy so that one element per member is sufficient for practical use. A framework based on DAM is also introduced for seismic design and discusses the issues in the application of DAM.