多向地震和多轴力系联合作用下结构构件的抗震设计

Seismic design of structural members under the combined action of multicomponent earthquake excitation and multi-axial forces

按反应谱方法进行结构构件的抗震设计时,对于三向地震分量作用的情形通常按平方和开方的方法进行组合来确定设计地震作用。梁、柱等结构构件一般承受着轴力和两方向弯矩等多种力系的联合作用,按平方和开方方法求得的轴力和弯矩代表三向地震作用下构件中有可能发生的轴力和弯矩的最大值,在N,Mx,My空间中形成一六面体的表面。但是轴力和弯矩的最大值一般不可能在同一瞬时发生,据此进行抗震设计将偏于保守。根据谷普达的研究,实际的极值包络在N,Mx,My空间形成一位于六面体内部的椭球体,因此建议了根据椭球体表面点进行N,Mx,My组合的设计工况方法。作者根据自己在建筑结构设计工作中的实践,研究了通过试算选择较为不利的设计工况,以及根据设计工况中的力系N,Mx,My进行组合求得断面中最不利的地震应力分布等,从而对这一问题取得了更为深入的认识。

For the seismic analysis of structural members subjected to three orthogonal components of earthquake ground motion based on response spectrum approach, the method of the square root of the sum of squares （SRSS） is often used to determine the design earthquake forces. Structural members, such as beams or columns are usually under the combined action of multi - axial force N and moments Mx and My. The maximum response of the member under the action of N, M My and evaluated by the SRSS method represents the probable value of each force or mo- ment, which forms the surfaces of a hexahedron in the N, Mx and My space. However, in general, the maximum force and moments do not occur simultaneously, the design based on this assumption leads to the conservative re- sult. The investigation of Gupta demonstrates that the real combination of multi - axial forces forms the surface of a ellipsoid inside the hexahedron in the N, Mx and My space. And he suggested to select several points on the surface of the ellipsoid for the design modes of combination of N, Mx and My. Based on the personal experience in the de- sign practice of architectural structure, the authors carried out some research on the trial calculation for the choice of unfavorable design modes and the evaluation of most unfavorable earthquake stress distribution in the section of structural member under the combined action of forces N, Mx and My etc. Some deep understanding of the problem is obtained.