Study On Several Problems Of Structural Seismic Analysis And Design Considering Earthquake Actions In Two Directions Simultaneously

Structural seismic analysis and design considering earthquake actions in two directions simultaneously is a complicated work, which includes the estimate of the input earthquake actions, the definition of the scope of structures considering earthquake actions in two directions and the combination of seismic effect. At the same time, in seismic design, further research is necessary on how to estimate and control the torsion effect and how to consider the accidental eccentricity. Some relative provisions about the above problems have been given in Code for Seismic Design of Buildings (GB50011-2001) and Technical specification for concrete structures of tall building (JGJ3-2002). But those provisions are not based on adequate research, and need to be reviewed or modified. Therefore, further study on seismic analysis and design considering two horizontal orthogonal earthquake actions simultaneously is significant for academic research and engineering design.The subject discussed in this paper is a part of the scientific research project " Structure seismic design considering two horizontal components of ground motions simultaneously ". In this paper, further research has been made on the scope of the structures considering earthquake actions in two directions, the combination method of the seismic effect caused by different inputs in two directions and the estimate of the accidental eccentricity and the torsion effect, which aims to offer sufficient theoretical and numerical material for amending the relative provisions in the codes. Moreover, the relative outcome in the different codes and references have been reviewed and compared. Based on the theoretical derivation and the results of model analysis, some conclusions have been got as following,â‘ The provisions about accidental eccentricity in GB50011-2001 and JGJ3-2002 may be not reasonable. It has been suggested the accidental eccentricity should be considered for all the structures in seismic design.â‘¡The torsion effect of structures has relations with the relative eccentricity and the ratio of the uncoupled translational stiffness and torsional stiffness. The torsion effect is different for the structures with eccentricity in one and two directions even if the relative eccentricity and ratio of the uncoupled stiffness are same. The ratio of the coupled periods defined in JGJ3-2002 can not exactly reflect the ratio of the uncoupled stiffness. JGJ3-2002 only controls the relative torsion effect in one direction is not reasonable.â‘¢The superposed effect of axial force caused by different seismic action inputs in two horizontal directions should be noticed. Omitting the superposed effect of axial force may lead to unsafe design for some columns. The scope of structures considering earthquake actions in two directions should not only be limited in the irregular structures.â‘£The combination method of seismic action effect caused by different inputs in two directions in GB50011-2001 has enough calculation precision for engineering design. However, the relative design response spectra in two orthogonal directions need more research.Finally, some suggestions and measures are put forward for improving the deficiency of relative provisions in GB50011-2001 and JGJ3-2002. The directions of further developing in this field are prospected.