中文摘要：

目前弹塑性反应谱的研究几乎都是以单自由度体系和单向地震输入为前提的，然而实际地震动的多维性，结构非线性的空间耦合特性使得基于单自由度体系的弹塑性反应谱存在局限性，为此本文进一步发展了双向地震作用下单质点双自由度系统的弹塑性反应谱模型。通过硬土、中硬（软）土、软土场地的178条地震记录作为地震输入，采用了不同以往的方法，建立了基于统计的强度折减系数设计谱。按3类不同场地，分析了延性系数、两水平主轴方向周期比对强度折减系数设计谱的影响。并根据统计结果，给出了便于工程应用的等延性强度折减系数简化设计谱公式。

英文摘要：

The strength reduction factor spectra of constant ductility factor for bi-directional ground motions is developed based on original theories by considering the multi-component earthquake excitation and coupled characteristics of structural response. The statistic formula of strength reduction factor spectra is improved in this paper. The effects of ductility ratios and period ratios of two principal axes on nonlinear response of systems under bi-directional earthquake excitations are discussed based on statistic analysis of 178 recordings for hard site, medium site and soft site. By the sufficient statistic analysis, the simplified formula of strength reduction factor design spectra of constant ductility factors is established, which is the foundation for forming the inelastic design demand spectra for structures subiected to bi-directional ground motions.