Seismic Response Analysis Of High-pier And Multi-pylon Cable-stayed Bridge Under Multi-support Excitation

High-pier and multi-pylon cable-stayed bridges are widely used because of their good spanning capacity and mature design and construction techniques.Mountainous terrains particularly need the use of high piers and multiple pylons.However,the highpier and multi-pylon cable-stayed bridge has the characteristics of low rigidity,high center of gravity,and large mass ratio of the tower and beam,so that its dynamic characteristics and seismic performance are different from the traditional low pier and double-pylon cable-stayed bridge.Therefore,the evaluation of the seismic performance of such bridges is to understand its response and damage characteristics under the earthquake and play an important role in ensuring the safety of the structure.The seismic response analysis of such long-span bridges with high-pier and multipylon generally takes into account the spatial variability of earthquake ground motion.The multi-support excitation input modes is more consistent with the actual situation.In order to understand and master the structural seismic performance of high-pier and multi-pylon cable-stayed bridge under complex site conditions and random ground motions,the research and analysis of high-pier and multi-pylon cable-stayed bridges under multi-support excitation has been carried.The main content includes the following:(1)Based on comprehensive reading and understanding of related literature home and abroad,the causes and disasters of the earthquake and the earthquake damage situation of the bridge structure were introduced and reviewed,the development,characteristics,and status of seismic research on multi-pylon cable-stayed bridges were summarized,then the theory of multi-support excitation seismic response analysis was introduced in detail.Finally,the fragility analysis of bridges was described and reviewed.(2)The multi-support excitation input modes was mainly introduced,in which the focus is on artificially simulating multi-point ground motion that satisfies the spatial variation characteristics.The related theories of the multi-support excitation random ground motion simulation method were combed in detail.At the same time,the corresponding MATLAB program was compiled.According to the response spectrum fitting,the multi-point ground motion non-stationary acceleration and displacement time history were generated,and then the 120 representative artificial ground motions were selected and used for the following calculation analysis.(3)Taking the Chishi Bridge as the object of analysis,the dynamic finite element model of the full bridge was established using OpenSees and Midas/Civil.The simulation methods of the key components of the bridge were described in detail,which took into account the simulation of pile-soil interactions.Finally,the dynamic characteristics of the bridge were analyzed.(4)Outlined the basic theory of seismic fragility analysis,determined the strengt h index and damage index of multi-point ground motion,and used the longitudi nal earthquake input method to calculate the vulnerable components of the bridge under uniform excitation and multi-support excitation.According to the earthquake responses,the fragility curves of corresponding component and system were generated,and the seismic performance of the bridge under the two excitation modes was compared and analyzed.(5)Outlined the basic principles,conditions,and design methods for the seismic isolation design of bridges,and then the layout and type of seismic isolation devices were introduced.The bridge using liquid viscous dampers was carried out to design seismic isolation.The nonlinear dynamic calculation of the bridge with isolation design was carried out under multi-support excitation,and the corresponding fragility curves were generated based on the calculation results.Finally,the seismic performance of the high-pier and multi-pylon cable-stayed bridge before and after the isolation design was compared and analyzed.