Study On Seismic Design Methods For Long-Span Spatial Structures

Spatial structures are widely used in long-span public buildings with its excellent structural performance and flexible architecture layout. This kind of structures is often of high safety level, the failure of which may cause huge loss of properties and even human's lives. Therefore, it is very important to ensure their safety by careful seismic design. In this paper, Laoshan Cycling Gymnasium for Beijing 2008 Olympic Games was taken as a case study and seismic design methods for long-span spatial structures are studied and discussed thoroughly.Mode superposition response spectrum (MSRS) analysis is the most general approach for seismic design. Due to the densely distributed natural frequencies and complex vibration modes, the response of long-span spatial structures under earthquake load is more unpredictable than that of other kind of structures. In this paper, typical earthquake records and corresponding response spectrums were used in the comparative analysis. It was proved that MSRS method would be accurate enough for seismic design of long-span spatial structure if enough vibration modes were taken in the superposition; The expression of general modal participation mass was then derived for spatial structures and mass participation factor was defined as the percentage of modal participation mass to the total mass of the structure system. The number of vibration modes needed to ensure the accuracy of MSRS analysis for long-span spatial structures was determined based on this mass participation factor. The superposition method of seismic reaction is also discussed. Whether CQC method or SRSS method should be adopted can be decided based on vibration characteristic of the structures.Time history analysis (THA) is an effective dynamic analysis procedure for structural seismic design. The earthquake records adopted as the input of THA should be compatible with the design spectrum. THA with earthquake records adjusted based on the design spectrum as input gives comparable results with MSRS method. It was then concluded that adjustment method based on the design spectrum should be used in THA of long-span spatial structures.