Seismic Performance Studies Of Integral Abutment Steel Bridges Considering Soil-Structure Interaction

Integral abutment bridges eliminate the expansion joints and bearings at the abutment,and the advantages include high design efficiency,faster construction,easier maintenance,reduced costs,and an enhanced capacity of resisting catastrophic events.However,the girder deformation has to be accommodated by the abutments,piles below abutments and soils to a large extent,and the stress state and failure mode also change because the abutment walls are connected monolithically with the girders.The paper investigates the influence of soil-structure interaction simulation methods on the seismic analysis of integral abutment steel bridges,and studies the failure process,ductility performance and seismic responses of integral abutment steel bridges.A 3-D finite element model of a bridge was established with the SAP2000 software.Modal analyses,nonlinear pushover and time history analyses were conducted to obtain the dynamic properties,plastic hinge development process,ductility performance,as well as the stress and deformation under different ground motion levels.Parametric studies were conducted to investigate the influence of design parameters of the integral abutment system,including the abutment size,backfill compactness,pile type,and foundation soil stiffness,on the bridge seismic performance.The main research conclusions are drawn below:(a)The direction of earthquake effects and the pile type change the hinging sequence of the bridge,and the foundation clay stiffness mainly affects the displacement when hinges form and fail,while the influence of the abutment size and backfill compactness is small.(b)Increasing the abutment height-to-thickness ratio and the backfill compactness can effectively enhance the safety reserve,and decrease the seismic response of abutment piles and pier columns.In high seismic zones,special attention should be paid to ensuring that the backfills are sufficiently compacted.(c)Compared with the prestressed concrete pile,integral abutment steel bridges supported by steel piles have better ductility capacity,larger failure displacement,and more energy dissipated.However,compared with the steel pipe pile and steel H pile bending about strong axis,when the pile type is weak axis bending steel H pile,the safety reserve and energy dissipated is fewer,and the pile-top section stress and column-bottom moment become larger.(d)Increasing the foundation soil stiffness around the piles can effectively reduce the pile-top displacement and column-bottom moment,and increase the safety reserve and ductility capacity.However,when the pile type is prestressed concrete pile,the energy dissipating displacement range becomes less.In high seismic zones,special attention should be paid to the obvious resistance decrease of medium clay with large deformation,which will make the seismic response of piles and columns increase.(e)The analytical precision of seismic response of abutment piles and pier columns has high sensitivity to soil-structure interaction simulation method and the PGA of earthquake wave,while the sensitivity of the abutment and girder response is lower.“M” method is recommended to be the simplified simulation method when calculating the soil-pile and soil-abutment interaction,and equivalent pile length can also be used when PGA is larger.