Analysis On Wave-passage Effect Of Long-span Grid Under Multi-support Excitation

With the rapid development of economy, people's life is getting more and more varied, and the demand for public buildings is more and more strict. Long-span space structures have been developed fast, such as large gymnasiums, exhibition halls, opera houses, train stations, airports, aircraft hangars, etc. The demand for the resistance of seismic and wind is more and more strict. Because of the natural frequencies of long-span space structures are intensive, the vibration modes are complex, and the spans of the structures are long, the spatial effects of seismics should be considered and be multi-point input. This paper will consider the seismic performance of the long-span grid from the wave-passage effect.Firstly, derive formulas and compare the methods of multi-support excitation, so as to make sure the large-mass method to be the multi-support seismic excitation method. Then, model the gymnasium of a university by ANSYS. Time-history analyse the model according to simple-support simple-direction excitation, multi-support simple-direction excitation, simple-support three-direction excitation and multi-support three-direction excitation seperately. The results show that the response of structure excited by three-direction is greater than excited by simple-direction. And its wave-passage effect is also greater. The most unfavorable condition is the three-direction seismic excitation spread by the main X-spindle of the structure. The wave-passage affects the displacement of the frame structure little. But the influence on the moment and the axial force by the wave-passage is great. When the apparent wave velocity is greater than 500m/s, the influence on the displacement and the moment by the wave-passage was beneficial. However, when the apparent wave velocity is less than 500m/s, the influence coefficients of the moment and the axial force by the wave-passage effect may reach 5 to 8, which's quite dangerous. Then, design four plans of the viscoelastic dampers for the grid to control the seismic response. The results show that the method, setting supports of the fluid viscoelastic dampers and replacing some chords by using the tube-type viscoelastic dampers, can control the displacement and axial force effectively. And it can reduce the wave-passage effect.