Dynamic Response Analysis Of Large-span Spatial Structures With Basement Under Multi-support Excitations

In traditional seismic response analysis of bridge structures under multi-support excitations, the earthquake response of the upper structure can be divided into three parts : the response of quasi-static internal force, the response of dynamic relative internal force and their covariance as a result of the relatively independent of basement.However,most large-span spatial structures usually have an integral basement.With the constraint of integral basement, structures’ quasi-static displacement can be ignored.In consequence of the phase-difference between the excitations imposed on the supports,which can be equivalent to imposing a torsional component to the foundation, the whole structures will twist.Accidental eccentricity can be used in the conventional structures’ seismic design.And multi-support excitations must be used in the large-span spatial structures’ seismic design. Both of them can cause structures’ torsion.From the seismic response analysis of rectangular frame structure,L-shape frame structure,frame-shear wall structure, multi-tower connected frame-shear wall structure, rectangular terminal building,L-shape terminal building under multi-support excitations,we have drawn the following conclusion:(1) Liao Yu who wrote “The analysis of the torsion effect of multi-tower and connected high-rise structure with whole basement under the earthquake action” studied accidental eccentricity and multi-support excitations’ influence on the dynamic response analysis of different structures.In order to link accidental eccentricity and multi-support excitations together and find out when multi-support excitations is equivalent to accidental eccentricity, apparent wave velocity vapp=1500m/s has been added to the study.By comparison,we can learn that when apparent wave velocity vapp=1500m/s is equivalent to accidental eccentricity’s effect to the dynamic response analysis of conventional structures.Accidental eccentricity will cause the torsion of each floor,but travelling wave effect only twist the bottom of structures.Therefore, the changes of proportions caused by accidental eccentricity has a uniform variation.When considering imposing multi-support excitations, the upper components’ changes of proportions is obvious greater than the bottom components’.(2) Dynamic response analysis of different structures is studied in order to find out the basement’s effect under multi-support excitations. Conclusions are drawn as follows. Without considering the basement’s effect, multi-support excitations have little influence on dynamic response analysis of weak link connected structures as a result of isolation bearing’s effect. On the contrary,considering the basement’s effect, structure under multi-support excitations will have a torsional vibration which causes an increasing of structures’ response.(3)Dynamic response analysis of rectangular terminal building and L-shape terminal building is studied in order to further study the influence of basement. We can find out that under bilateral seismic excitations,the relation between seismic response and apparent wave velocity is very irregular. But the changes of proportion still have the characteristic that response increasing with the decreasing of apparent wave velocity. What’s more, the response of models considering basement’s effect is greater than models without considering basement’s effect. Thus, the basement’s influence can’t be ignored in the dynamic response analysis of large-span spatial structures under multi-support excitations.It’s very necessary considering the influence of basement in structural seismic design.Furthermore,when considering the effect of the basement, L-shape terminal building’s components’ changes of proportions are great than rectangular terminal building’s components’ which have the same coordinates.