Seismic Analysis And Design Method Of Long-Span Spatial Structures Considering Spatial Variation Of Ground Motion

In the recent years, a number of long-span spatial structures with novel patterns and large scale have been built in China. Compared with traditional structures, the long-span spatial structures are more characterized by large spatial dimensions, which inevitably induces that it is inaccurate to ignore the influence of spatial variation of ground motion. However, the spatial effect of long-span spatial structures is not included in the current seismic design code, so it is quite urgent to establish a seismic design method for long-span spatial structures, in which the spatial variation of ground motion should be taken into account.In this dissertation, based on the theories of random vibration, algorithms for analyzing the random seismic response of long-span spatial structures are improved, and a model of earthquake ground motion is established, in which the spatial seismic effects is taken into account. Moreover, a practical method for long-span spatial structures with general consideration of spatial seismic effects is proposed in this dissertation. The outline of the main work and achievements are concluded as follows:(1) Based on the existing pseudo-excitation method, the algorithms for multi-excitation seismic analysis are improved. The improved algorithms are more efficient for random seismic analysis of long-span spatial structures and more practical for practical seismic design. Moreover, according to the improved algorithms, computer programs are compiled.(2) For the defects of the existing Ritz vector superposition method, a new method with Rayleigh quotient shift is proposed. Problems of the cut-off criteria for Ritz vectors are discussed and some correction measures are given. Proper orthogonal decomposition (POD) technique is applied to compute the first several statistically dominant POD modes which are regarded as spatial distributions vectors of earthquake loadings for the generation of Ritz vectors. Then, the Ritz vector superposition method and the proper orthogonal decomposition technique are combined to improve the efficiency of multi-input seismic analysis for long-span spatial structures.(3) A relationship between relative displacement spectrum and the mean peak value of relative displacement responses is established. According to the piecewise curves of response spectrum given by the code for seismic design of buildings, the PSD piecewise curves of ground acceleration are provided. And based on the existing stochastic models of ground motions, a multi-dimensional, multi-input stochastic model of ground motion is established, and three-dimensional translational motion components and spatial variation of the ground motion are taken into account as well.(4) The influences of wave passage effect, partial coherence effect and local site effect on seismic responses of long-span spatial structures are studied in both theoretical analysis and numerical simulation. Conclusions are given on the variation of the peak response due to different apparent wave velocities, the variation of partial coherence effect due to different span and excitation frequency, and the influence extent of local site effect on response of urban long-span spatial constructions. These conclusions provide directions to seismic design of long-span spatial structures.(5) The influences of spatial variation effect on the responses of long-span spatial structures are studied through both theoretical analysis and numerical simulation. According to all of these results, a general design procedure and some suggestions on seismic design of long-span spatial structures with consideration of spatial variation effect are provided.