Study On Elasto-plastic Seismic Performance Of Small-and Mediam-span Space Frames

Analysis on elasto-plastic seismic response is the main basis of space frame’s aseismic measures and performance-based seismic design under precautionary intensity earthquake and rare earthquake. But few of quantitative analysis is carried out. Based on investigation of architectural function and structural form of primary and middle school’s indoor stadiums,10typical small-and medium-span grid models are employed, and elasto-plastic dynamic performances of whole structure under medium, rare and near-field earthquake are researched.The main study contents and conclusions are as follows:(1) The10typical grid models are determined by the full-stress design under non-seismic load cases. Considering the interaction with substructure, the dynamic characteristic and response under frequently occurred earthquake are analyzed. The research shows that the sections of small-and medium-span space frames rarely need adjustment because of small earthquake checking, and seismic precautionary demand of "no damage during frequently occurred earthquake" is easily satisfied.(2) The elasto-plastic response characteristics of grid structures are analyzed under precautionary intensity earthquake and rare earthquake. The results reveal that the small-span space frames can meet the standard of "no damage during precautionary intensity earthquake" A few of plastic members occur for medium-span space frames. After the action of rare earthquake, upper and lower chord members near the abutments of medium-span space frames appear obviously plastic deformation, but the precautionary demand of "no collapse under rare earthquake" is satisfied.(3) The influence of different conditons on space frame’s seismic response is analyzed. The results reveal that the span and intensity are the most important factors. The symmetry of lower frame mainly affects the distribution of plastic members. The spring support can only decrease the seismic effect to a certain extent. Different earthquake waves give rise to obvious difference of elasto-plastic response and residual displacement, but have little influence on the distribution of plastic members.(4) The sections of grid structures are designated to be satisfied with the level of "elastic design under moderate earthquake". The steel consumption increases within2%. The precautionary requirement of "repairable under precautionary intensity earthquake" is satisfied and the problem of complicated repairing is avoided. And the residual displacement can also meet the demand of "no collapse under rare earthquake". When the precautionary intensity is8degree (0.2g), the plastic deformation of the medium-span space frames which are designed according to the standard of "elastic design under moderate earthquake" obviously decreases after the action of rare earthquake. So they are suggested to be designed according to the standard of "elastic design under moderate earthquake".(5) The unidirectional artificial wave which contains no pulse effect and near-fault ground motion records which contain typical velocity or acceleration pulse effect are input into grid models. The calculations show that the acceleration pulse resulted in forward rupture directivity produces several times of strain and displacement response compared with conventional earthquake. The influence of velocity pulse resulted in fling step on seismic response is not very significant. On the structural design of grid in the near-fault region, the amplification effect of forward rupture directivity on the elasto-plastic deformation must be considered.