A Study On The Displacement Input Model For Seismic Response Analysis Of Long-span Seismically Isolated Structures

The large-span isolated structure has the advantages of large span,strong functionality,and remarkable seismic performance.At present,many specifications adopt consistent vibration input to the structure.For a structure with small space size and small span,the consistent vibration input is basically satisfactory,but for large-span structures,seismic waves are subject to ground motion during propagation.The impact of spatial variability,so multi-point excitation needs to be considered at this time.In this paper,the application of displacement input model in large-span isolation structure is studied by time-history analysis.The main work in this research process is as follows:(1)The system explains the theoretical mechanism of the commonly used computational model of large-span structure under multi-point excitation and the applicable scope of each model,including displacement input model,acceleration input model,large stiffness method input model and large mass method input model.At the same time,the differences between the displacement input model and the large stiffness method and the large mass method are expounded from the aspects of theoretical formula,input method and error reason.(2)For the common structure,from the derivation process of the displacement input model and the acceleration input model,it can be seen that the two input models ignore different damping terms,which will cause differences in the calculation results,and the magnitude of the difference is related to the damping component used.The shear model example is used to verify that the deviation of the calculation results of the two input models is mainly from the mass damping part.(3)The displacement input model can directly determine the absolute displacement of the structural response.It is suitable for linear systems as well as nonlinear systems,so it is widely used in engineering.However,the displacement input model ignores a damping force during the derivation process.For the isolated structure,ignoring the coupling damping term may cause a large calculation error.By comparing the displacement input model with the calculation model without ignoring the coupled damping term,the error of the coupling damping term neglecting the structural seismic response is studied.At the same time,the error of the seismic response of the structure using the displacement input model is studied when different damping ratios and different seismic waves are used.(4)For the large-span isolated structure,artificial synthetic ground motion is used to study the error caused by the displacement input model to the seismic response.At the same time,considering the different ground motions caused by different structural spans,the error caused by the displacement input model to the structural calculation results is applied.