Research Of Seismic Vulnerability For High-Pier Large-Span Concrete Continuous Rigid Frame Bridge Based On Opensees

Bridges play a pivotal role in the transportation system, a slight move in one part may affect the whole situation. This thesis sets a railway high-pier long-span prestressed concrete continuous rigid frame bridge as the research background, using analysis software OpenSees to build the nonlinear finite element model to study the seismic vulnerability with the medthod of nonlinear time-history dynamic analysis. The main contents are as follows;1. The developments and mechanical characteristics of high-pier continuous rigid frame bridge, the performance-based seismic design, the analysis methods and the research status of seismic vulnerability on bridges are introduced through literature at home and abroad.2. The whole procedure of building the finite element model of the bridge with the nonlinear analysis software OpenSees is generalized. The material constitutive relationship and definition of fiber cross section are introduced. A simple comparison between the OpenSees model and the Midas model has been done through eigenvalue analysis.3. The structural failure criteria and the structural damage assessment methods are introduced in detail, According to the mechanical properties of prestressed concrete continuous rigid frame bridge, the vulnerable location of the piers are analyzed. Moment-curvature analysis on the key sections of the vulnerable location has been taken, the limited value of the various damage state are determined by selecting curvature ductility ratio as the damage index. The influence of the axial compression ratio and the longitudinal reinforcement ratio on the vulnerability index is discussed subsequently.Showing that the boundary value of each damage state decreased with the increase of the axial pressure ratio in a certain range(from 0.05 to 0.3). And the decrease amplitude slows with the increase of axial compression ratio. As the reinforcement ratio increase, the boundary curvature ductility ratio values of each damage state tend to be stable.4. Combine the horizontal acceleration response spectrum in the seismic design code with the bridge site conditions, the response spectrum is transformed into the power spectrum and the amplitude and phase are calculated, some artificial non-stationary ground motions have been synthesized5. The seismic vulnerability of the bridge subjected to transverse and longitudinal ground motion is analyzed respectively.Set PGA as the ground motion intensity index, the seismic fragility curves are drawn out. The results show that the main piers have good seismic performance. Under the action of longitudinal ground motion, the pier top of the bridge is more prone to damage than the pier bottom, while the pier bottom is more likely to be damaged than the pier top when it suffers the action of transverse ground motion. And the damage probability of the piers under the action of longitudinal ground motion is much greater than the damage probability of the piers which are subjected to the action of transverse ground motion. Meanwhile, the effect of site types on seismic fragility curves is discussed, the results show that the structural seismic vulnerability increases as the site condition change from hard to soft when it is under the same peak acceleration.