Study On The Characteristics Of Seismic Response Of Bridge With High Piers And Long Span

In seismic design and seismic assessment of bridges, it is necessary for us to understand dynamic responses of bridges under strong earthquakes, especially the responses of bridges with high piers or long span. Because the heights of piers of high-pier bridges vary greatly, the earthquake behavior of high piers is quite different from that of low piers. So, it is necessary to analyze the earthquake behavior of high piers and low piers. Just like the high-pier bridge, dynamic characteristics of long-span bridges with long natural period are very complicated too. To study the influences of duration of strong earthquakes on structures can help us comprehend the earthquake responses of the structures and improve their seismic capacity. During the last twenty years, many bridges with high piers or long span have been built or being built, but few of them have suffered from earthquakes. So there are not enough earthquake data and experiences that can be used in seismic design of such bridges. Because of this reason, several questions are investigated in this dissertation.1. Earthquake behavior of high piers, low piers and major beam of Continuous Rigid Frame Bridges with high piersBased on two continuous rigid frame bridges, the finite element models are formed. Response spectrum method and time history method are employed to analyze the internal force responses and displacement responses of high pier and low pier, and earthquake behavior of major beam and piers. The study indicates that: a) the amplitude of the internal force and displacement of high pies is larger under earthquakes transverse to bridges, the amplitude of the internal force and displacement of low pies is larger under earthquakes parallel to bridges, and the damage probability of low pier is larger than that of high pier; and b) the amplitude of vertical displacement response is smaller than that of horizontal displacement response.2. Influences of the duration of strong earthquakes on bridgesIn this dissertation, six artificial acceleration time histories with different durations of strong earthquake based on two response spectra are produced. Three bridges with different dynamic characteristics are analyzed under the excitations of these artificial acceleration time histories. The result shows that influences of the duration of strong earthquakes on bridges are connected withthe characteristics of spectra and the structures. The bridges show big forces and displacement under the excitations of the long-duration artificial acceleration time histories compounded according to the spectrum including abundant components of long periods. On the contrary, the bridges with long natural period show big forces and displacements under the excitations of the short-duration artificial acceleration time histories compounded according to the spectrum including abundant components of short periods. 3. The analysis of nonlinear impact earthquake response of simple-supported frame bridgewith high piersBased on a simple-supported frame bridge with high piers, a new model considering the role of bearings and the impact between frames is brought forward. Modal analysis and earthquake response analysis of the bridge are carried out. The result shows that impact force between the frames of bridge is related closely to the stiffness of the piers. The bigger the stiffness is, the bigger the impact force is.Finally, the research in this dissertation is summarized, and the existing problems and the prospective work are pointed out.