| The term spatial variation of seismic ground motions denotes the differences in amplitude and phase of seismic motions recorded over extended areas.Comparing with the assumption of uniform excitation,the spatial variation of seismic ground motions has an important effect on the response of lifelines such as bridges,pipelines,communication transmission systems,etc.In the past,people usually pay more attention on the study of bridge structural response to multi-support excitations.The seismic response of building structure is often ignored.With the development of engineering technology,the span of building structure becomes larger,can even be hundreds meters.Considering the influence of spatial variation of ground motions in building structure design has become the consensus of academic and engineering both in internal and international.Many scholars have analyzed the seismic responses with different types of large-span building structures and realized the importance of considering the influence of spatial variation of ground motions in building structure design.However,due to the particularity of engineering structures,the structures with the same type may have large differences in seismic response.So it is difficult to get the seismic design method for this type of structure.In order to study the influence mechanism of spatial variation of ground motions to large-span building structures and put forward the seismic design method for the specific type of structures,this paper selects the simplified model of bidirectional symmetric large-span spatial structure as the research object and study the influence rules of the structural seismic response by changing the parameters of ground motions and structures.The main work in this dissertation includes several aspects as follows:(1)The analysis method of structural seismic response to multi-support excitations is studied.A simplified algorithm for seismic response analysis of two supporting structures to multi-support excitation is proposed and its accuracy analysis is also conducted.The multi-support pseudo excitation method is simply introduced and its practical solution form is given.(2)The influence mechanism of seismic response of large-span spatial structures to three kinds of earthquake spatial variability effects is studied.The formulae of power spectral density of structural seismic response are derived by the multi-support pseudo excitation method.The relative multi-support excitation effect items are obtained to study and interpret the influence mechanism of structural response to multi-support excitations.Different conditions are selected to analyze the influence rules of structural response to wave-passage effect,incoherence effect and local site effect.The maximum response is calculated to judge the influence degree of the structure.(3)The influence law of seismic structural response to multi-support excitations with different number of span and different supporting systems is studied.As an example,the multi-support excitation effect items of a two span structural model are derived and compared with those of single span structure to analyze the influence mechanism of bearing number to structural response.The influence degree of structure is studied by analyzing the maximum response distribution.This method is extended to the multi-span structure to study the influence rules of structural response with increasing number of span.The influence of structural response to multi-support excitation with different supporting system is also studied.(4)The influence mechanism of structural torsional response to multi-support excitations is studied.The expressions of power spectral density of roof torsional response are derived by the multi-support pseudo excitation method to study the structural maximum torsional response distribution.The conception of ‘the equivalent torsional eccentricity’ is put forward and compared with ‘the accident eccentricity’ given by the Chinese seismic code to judge the influence degree of structural torsional response.The influence rules of structural torsional response to multi-support excitations are studied by changing number of spans,supporting form,number of stories,torsional period ratio,site characteristics and lateral stiffness of column.(5)The structural random seismic response to multi-dimensional and multi-support excitations is studied.Firstly,the solution form of the multi-dimensional and multi-support pseudo excitation method is derived.Secondly,the differences of structural response to multi-support excitations between multi-dimensional and single-dimensional are studied by conducting numerical analysis.Finally,the influence rules of structural response to multi-dimensional and multi-support excitations are studied with the changing the angle of incidence.(6)The seismic design method of large-span spatial structures under spatial variation of seismic ground motions is put forward.Based on the structural response law of the simplified model obtained before,the seismic design method for the specific type of structure is proposed: including the handing method of wave-passage effect,incoherence effect and local site effect,the calculation method of the minimum span to consider the wave-passage effect is also put forward;the calculation formulae of the total structural equivalent torsional eccentricity and the corresponding design reference advice of structure under multi-dimensional and multi-support excitations. |
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