Analysis Of Pulsed Seismic Response Of Dwarf Tower Cable-stayed Bridge In Near Faults

In recent years,the use frequency of extradosed cable-stayed bridge is getting higher and higher.It not only has the stress characteristics of continuous beam bridge,but also has the partial stress characteristics of cable-stayed bridge.At present,there are relatively few studies on the response of extradosed cable-stayed bridges under near-fault pulse-type earthquakes in China.Therefore,this paper will study the development history of extradosed cable-stayed bridges and the current stage of near-fault pulse-type earthquakes at home and abroad,and draw out its shortcomings and propose new research directions.Based on the engineering example of Guohe Eight Bridge,the seismic response law of the bridge in the near fault area is analyzed.The following four aspects are studied.(1)The basic theory of seismic resistance of bridge structure is expounded,including response spectrum method,dynamic time history method and random vibration method.The Newmark-β method,Wilson-θ method and response spectrum method of dynamic time history method are introduced in detail.Several representative mathematical models of random vibration are listed.The mathematical fitting relationship between the pulse period of the pulse-type earthquake and the PGA is briefly introduced.The relationship between the near-fault velocity pulse proposed by Mavroeidis et al.and the three models of the near-fault velocity pulse of Makris(unimodal,bimodal,and multimodal)are introduced.(2)Ansys finite element analysis software using parametric language,using double main beam method to establish the finite element model,and the cable sag effect and geometric nonlinear effects are taken into account.Through the method of nonlinear calculation,the relevant results can be obtained.The natural vibration period of the eighth Guohe Bridge is 2.32 s.The difference between the fundamental frequency of the whole bridge and the design result is only 0.85%.The first 10 modes are basically consistent with the design.The maximum difference between the calculation results of the full-bridge cable force and the designed cable force is 3%,which meets the requirements of relevant specifications.Therefore,the model is correct and has certain credibility.(3)Using the seismic records of the PEER seismic database,the near-fault pulse-type earthquakes are identified,and the near-fault pulse-type earthquakes with or without velocity pulses and the near-fault pulse-type earthquakes with large fault distances are selected.Through the response analysis of the extradosed cable-stayed bridge under the action of nearfault earthquake with or without velocity pulse,it is concluded that the effect of earthquake with velocity pulse on the structure is stronger than that without velocity pulse.Considering the traveling wave effect on the structural response of near-fault pulse-type earthquakes,the study shows that the response of near-fault pulse-type earthquakes is greater than the uniform excitation to the structure.It is suggested that the seismic analysis of traveling wave effect should be considered for bridges within the fault range.The response analysis of the intersection angle between bridge strike and fault orientation under near-fault pulse-type earthquake action shows that there is an unfavorable intersection angle between 45° and 90°.(4)Through the research on the response of low-pylon cable-stayed bridge under the vertical effect of near-fault pulse-type earthquake,it is shown that the response value of the recommended value of the specification(0.7 times of the horizontal component)is unsafe.It is suggested that this value should be appropriately increased to 1.0 times and above.When the recommended value of the specification is increased to 1.0 times,the response value of the relevant monitoring points is increased by 15%.The response to the cable force of the cable is not significant,and the response to the main tower of the main beam is more obvious.It reduces the response of the bottom of the main pier,which is beneficial to the structure.On the basis of considering the recommended value of the code,further research on the selection of ground motion is carried out.In the study of the selection of vertical ground motion,it is found that the response of the actual vertical ground motion to the structure is more significant than that of the vertical ground motion recommended by the code,indicating that the actual vertical ground motion time history record should be selected when considering the influence of near-fault pulse-type earthquake on the structure.It is found that the response intensity of three different types of earthquakes to the structure is arranged in the order of near-fault pulse-type earthquakes,near-fault non-pulse-type earthquakes,and near-fault earthquakes with large fault distances.Figure [59] table [36] reference [55]...