Structural eccentricity plays an important role in the seismic design of buildings. According to various seismic design codes, it is one of the parameters which define whether a building may be considered as regular in plan. Structural eccentricity is defined as the distance between the center of mass and the center of rigidity. However, the center of rigidity is rigorously defined in single story buildings and in some special classes of multi-story buildings, e.g. isotropic ones, under the assumption of fixed based conditions. The present paper deals with single story and multistory asymmetric buildings that possess a real elastic axis under the assumption of fixed base condition and examines the existence or not of an elastic axis under soil structure interaction effects. The flexibility matrix and the loading vector are defined under flexible base assumption and the elastic axis is determined based on the notion of twist center. Mathematical formulas are derived which provide the coordinates of the elastic axis. Numerical examples are presented which investigate not only soil-structure interaction effects but the influence of various loading vectors as well. In general, soil-structure interaction extinct the real elastic axis; hence an optimum torsion axis must be defined. Moreover, soil-structure interaction decreases the structural eccentricity at each story level.

结构偏心率在建筑物的抗震设计中起着重要作用。根据各种抗震设计规范，它是定义建筑物在计划中是否可以视为规则的参数之一。结构偏心率定义为质心和刚度中心之间的距离。然而，在基于固定条件的假设下，在单层建筑和多层特殊建筑的某些特殊类别（例如，各向同性的建筑）中严格定义了刚度中心。本文讨论了在固定基础条件下具有真实弹性轴的单层和多层非对称建筑物，并研究了在土-结构相互作用作用下弹性轴的存在与否。柔韧性矩阵和载荷矢量是在柔韧性基础假设下定义的，而弹性轴是根据扭曲中心的概念确定的。推导了提供弹性轴坐标的数学公式。给出了数值示例，这些示例不仅研究了土-结构相互作用的影响，而且还研究了各种载荷向量的影响。通常，土-结构相互作用不存在真实的弹性轴。因此必须定义一个最佳的扭转轴。此外，土壤-结构相互作用降低了每个楼层的结构偏心率。给出了数值示例，这些示例不仅研究了土-结构相互作用的影响，而且还研究了各种载荷向量的影响。通常，土-结构相互作用不存在真实的弹性轴。因此必须定义一个最佳的扭转轴。此外，土壤-结构相互作用降低了每个楼层的结构偏心率。给出了数值示例，这些示例不仅研究了土-结构相互作用的影响，而且还研究了各种载荷向量的影响。通常，土-结构相互作用不存在真实的弹性轴。因此必须定义一个最佳的扭转轴。此外，土壤-结构相互作用降低了每个楼层的结构偏心率。