Study On Seismic Response Characteristics Of Extradosed Cable-stayed Bridge With High Pier And Long Span

The rapid development in the western region of China witnesses a large number of bridges have been built,and due to the limitation of topography and geomorphology,the number of bridges with high piers and long spans is increasing.High-pier and longspan bridges have low pier stiffness and large pier mass,and their dynamic characteristics and seismic performance are different from those of traditional bridges with medium and low piers.There is a lack of seismic design code for high pier and long span bridges in all countries.At the same time,due to the high variability of seismic waves in time and space,high-pier and long-span bridges generally need to consider the influence of multi-point excitation.Compared with low piers,the slenderness ratio and axial compression of the high pier are relatively large,which may cause large deformations under horizontal earthquake,resulting in the obvious P-Δeffect caused by the gravity load from the upper structure,which makes the actual response of the structure deviate from the results of the first-order analysis.The research on the seismic performance of high-pier and long-span bridges urgently needs to be further deepened.Therefore,taked an extradosed cable-stayed bridge with high pier and long span as supporting project,this article combed the present situation of earthquake damage and seismic analysis methods of bridge,and then focused on summarizing the development and seismic performance research status of high pier and long span bridges.The primary points s are as follows:(1)The elastic static and dynamic models were simulated,then the basic characteristics were dynamically analyzed.On this basis,the seismic response feature under E1 earthquake were studied by using response spectrum method and linear time history analysis method.The results showed that the bottom of pier and the pier-beam joint of the main girder are all control sections.and considering vertical earthquake greatly increases the seismic response of main girder,so the seismic response characteristics of main beam should be paid special attention.(2)Furthermore,the seismic response characteristics of the main girder of high pier and long span bridge were studied,and the internal forces and stresses of the bridge under live load were calculated.The response of main girder under the live load and the earthquake were compared to determine whether the seismic effect will control the design of the main girder of the high-pier and long-span bridge.Meanwhile,the influence of pier stiffness on seismic response was researched.On the basis of the results,the internal force response of the main girder of the high-pier bridge under the earthquake is equivalent to or even exceeds that under the live load,which is different from the conventional bridge.Therefore,the seismic effect on the main girder should be considered,and it is necessary to select an appropriate pier stiffness to reduce seismic response of the bridge.(3)Different seismic wave parameters were selected to deeply study the influence of P-Δ effect on the dynamic characteristics and seismic response of bridges with different pier heights,and the influence of displacement spectrum on P-Δ effect was analyzed.It showed that the dynamic P-Δ effect is relevanted to the dynamic feature of the structure and the frequency spectrum feature of the earthquake.When the static stability coefficient θ is greater than 0.04 and the basic period of the structure is located in the region where the seismic wave displacement response spectrum increases sharply,P-Δ effect may increase the internal force and displacement.Its influence may exceed10%,so it is necessary to consider its adverse effects.(4)The time history analysis of the structure considering the influence of the traveling wave and different wave speeds was carried out.It showed that considering the traveling wave effect reduces the seismic response of the pier,so it can be ignored,but it will lead to a significant increase in the vertical displacement,axial force and bending moment of the main girder,and the influence is greater with the decrease of wave velocity,so special attention should be paid to the influence of traveling wave effect on the seismic design of the main girder.