Analysis Of Multi-support Seismic Input For The Long Span Spatial Lattice Structure

The seismic input is the precondition and base of structural response. It is assumed in the conventional coherent-vibration input that all of the support points have the same ground movements, while carrying on the analysis of the long span spatial lattice structure to response of earthquake. This is equal to treat foundation as rigid body. If the structural size is far smaller than the wavelength of earthquake, this kind of hypothesis can be accepted. Actually, because the difference of the seismic character and geology and seismic transmission, the ingoing seismic wave is variable on the time and space, even other conditions are completely consistent, the time which each support point of aqueduct receive seismic wave is fall behind each other, because the distance of support points to the focus of earthquake is different, in same time, the movement which received by each support point is different, this is the question of multi-support seismic input. Using ANSYS soft ware and basing on the model of the long span spatial lattice structure, this text builds two double-layer reticulated shell model, whose span are 80 meters and 160meters. Basing on the modal analysis of the structure and ANSYS Parameter Design Language, the program of coherent-vibration input and multi-support seismic input are compiled. Using these programs, this text calculates the dynamic response of model. This text chooses 7 nodes and 8 cells to compare the differences between coherent-vibration input and multi-support seismic input. In the analysis of multi-support seismic input, this text analyses the influence of velocity of seismic wave and the span of the structure on the response of earthquake. Analysis results in the conclusion: the result of multi-support input is larger than coherent-vibration input. In vertical wave, vertical displacement, vertical acceleration and internal force of multi-support input are larger than coherent-vibration input, the magnification coefficient of maximal value are largest when the velocity of seismic wave is equal to 200m/s. With the increasing of velocity, the most magnification coefficient are decreasing;In transverse wave, the magnification coefficient of transverse displacement, transverse acceleration and internal force are also largest when the velocity of seismic wave is equal to 200m/s. But some node's transverse displacement, transverse acceleration and some cell's internal force are smaller when the velocity of seismic wave is equal to 400m/s, than them when the velocity of seismic wave is equal to 800m/s.