Analysis Of The Wave-passage Effect On Hybrid Large Space Truss With Special-shaped Grids

Hybrid Large space truss with special-shaped grids is a mixed structural system composed of different material structural systems,whose roof is usually made of steel space truss,whereas lower part is of reinforced concrete structure system.Its safety now becomes a hot spot with the increase of buildings with large-span spatial structures,and its requirements on the seismic behavior of the structure itself also get stricter.Because a hybrid structure of large space truss has the characteristics of high vibration frequency,complex vibration modes,besides its large span,so that in the research on the seismic response of this kind of structure the spatial effect of ground motion should be taken into account and multi-point input be adopted.This paper starts with the wave-passage effect to investigate the seismic performance of hybrid large space trusses.In this paper,a practical project of hybrid large space truss with a plan dimension of 75.6m by 33.9m has been taken as an example.SAP2000 analysis software was used to build its overall model,and then the dynamic and time-historical analysis were carried out under unidirectional multi-point excitation and bidirectional multi-point excitation,and the results were compared with the structural responses under coherent input.The variation of the influence coefficient of the traveling force of the internal forces of the structural support columns and the internal forces of the truss members under various working conditions were studied.Summary was given on the structural seismic response law under multi-point input.Through the work above,following conclusions have been reached:The first three modes of the structure are the main modes of vibration.The first mode is the translational vibration in Y direction,with a cycle of 1.043972s;the second mode is translational vibration in X direction with a cycle of 0.698624s;and the third mode is rotational vibration around Z axis with a cycle of 0.669644 s.And the accumulated mass participation factor meets the requirement of more than 90% specified in the code.For the supporting column in the lower frame,the influence of wave-passage effect is to be taken into account,so that based on uniform excitation,the column moments at the middle of the truss spans should be magnified by 1.4,shear forces by 1.25;whereas the bending moments of the columns at the sides of the truss should be enlarged 1.3 times,and shear forces 1.4 times.For the upper space truss with special-shaped grid,the axial forces in the upper chords,lower chords,and the diagonal web members near the supporting columns should be modified by a factor of 1.45.The large mass method can impose the ground acceleration onto each supporting point of the structure,yet the calculation is convenient,and can obtain relatively real response of the structures,therefore should be applied to the analysis of wave-passage effect on hybrid large space truss.