Study On Seismic Design Theory Of Irregular Girder Bridges With High Piers

With the implementation of Western Development Program in recent years, a lotof highways and railways are planned and built in West China. The bridges with highpiers that span rivers, channels and valleys, belonging to typical irregular girderbridge, are key projects in main lines of communication. Because of given servicerange, seismic design criteria home and abroad are unavailable for these bridges. Theseismic design theory of irregular girder bridges with high piers is systematicallystudied to discover its complexity of structural ductility demand and ductility capacitysubjected to earthquake excitation in this dissertation. The main contents are asfollows:●Such aspects of research are reviewed as bridge seismic design philosophy,structural performance index system of seismic design, calculated method ofdisplacement ductility capacity and seismic analysis of bridges with high piers, basedon the comprehensive reading and understanding of related literature home andabroad.●Two analytical models of bridge pier are developed based on elastic-plasticbeam-column element and elastic-plastic fiber beam-column element. Structuralseismic demands such as formation of plastic hinge, expansion of plastic zone, plasticrotation and top displacement, are discussed in detail, and the influence ofelastic-plastic beam-column element divisions on seismic demand is analyzed andcompared. Finally, the applicability of two analytical models is discussed in seismicdemand analysis of tall bridge pier.●Increment Dynamic Analysis (IDA) is introduced into computing displacementductility capacity of piers, and IDA and pushover analysis are applied ondisplacement ductility index of different pier models. The influence of earthquakespectral character, higher vibration modes, self-mass of piers, material nonlinearitylevel on displacement ductility capacity of frame member is analyzed, and IDA isidentified as a feasible and reliable solution of displacement ductility index. After that,the computing means and mechanical explanation of displacement ductility capacityof high piers, proper performance index is investigated.●Take account of modal mass participation coefficients as reference variable, threebridge models with different height and structural style are created and analyzed to get yield displacement and ultimate displacement with IDA and pushover analysis alonglongitudinal direction or transverse direction of bridge. According to comparativeresults, the influence of higher vibration modes and self-weight on damage and failure,nodal displacement, cross-section curvature and lateral load or inertial forcedistribution at critical state is discussed. Instead of top displacement, cross-sectioncurvature is served as performance index to confirm its corresponding structuraldamage state of irregular girder bridges with high piers.●Based on performance index system of seismic design and research productionabove, Key Cross-section Curvature-Based Seismic Design philosophy is put forwardfor irregular girder bridges with high piers.