Time-dependent Seismic Performance Of Concrete Bridges With High-rise Pile Cap Considering The Foundation Scour

As an important junction in the transportation lifeline system,bridge engineering has important economic and strategic significance.The bridge’s lifetime safety is very important.Among the many factors that aff ect the bridge’s use security,both of earthquakes and floods are the two main reasons.For the cross-water bridges that located in seismically act ive zone,they have to face the threat from two natural disasters,earthquake and flood erosion.Therefore,takes a multi-span concrete continuous rigid frame bridge on a river in western China as an example,this paper conducts the risk analysis of the flood erosion depth,and studies the influence of foundation erosion effect on the time-dependent seismic performance of the concrete bridges with high-rise pile cap.The main research work is as follows:(1)Based on the calculation method of scouring depth in the HEC-18 code,the deterministic and uncertain analysis of the foundation scouring depth of the case-study bridge is carried out,respectively.The flood frequency statistical analysis is carried out on the historical flood flow of the river,and the uncertainty analysis method is used to obtain the flood hazard curve.Then the scouring depth risk curves o f the case-study bridge are obtained for different flood events.(2)For seven flood events with different risk levels,different Open SEES finite element models are established for case-study bridge.Multiple ground motions are selected for nonlinear time history analysis.The results reveal that,with the increase of the scouring depth,the natural vibration period of the bridge structure and the peak displacement response of each component(main beam,pier and pile foundation)will gradually become large r.The peak internal force of the pier top section and pile top section increases with the increase of the scouring depth,but the peak internal forc e of the pier bottom section decreases accordingly.With the increase of scouring depth,the collision effect at the expansion joints for the side span and the deformation response of the abutment change significantly.(3)Considering the influence of uncertainty derived from the ground motion,100 seismic waves are selected for nonlinear time-history analysis,and then the time-dependent seismic fragility curve of the example bridge is established.The results reveal that,the change of scouring depth has a greater impact on the seismic fragility of the bearing in the transverse direction.As the service time of the bridge increases,the seismic failure probability of the pier top section gradually increases,while the s eismic failure probability of the pier bottom section shows a downward trend.Meanwhile,the seismic failure probability of the pile top sectio n and the abutment increases significantly.