Study On The Differential Settlement Of Widening And Existing Bridges And Its Effects On Superstructure

In view of the widening of concrete bridges in widened highway projects,this paper systematically studies the main problems in the whole process of expansion and operation due to differential foundation settlements.Through the FEM,the bridge pile-soil model and the upper widened structural model were established,and the influence of the new pile construction process near the old foundation and the internal force and deformation of the upper structures caused by differential settlements were simulated.Through the simulation of Mesri soil creep model,the settlement development of new and old foundations are predicted.The main work and conclusions are as follows:(1)This paper summarizes features of different connection schemes of the new and old bridges in widened bridge projects.Combined with the subsequent disease state of the existing widening project,according to the different widening schemes and the structural characteristics of the connection methods,the corresponding suggestions are proposed;(2)By using the ABAQUS software,the finite element model of the bridge foundation and adjacent soil is established.The calculation and analysis show that the process of new pile drilling has less effect on the adjacent old piles,and the new bridge load has a greater additional effect on the old piles.After the upper load of the new bridge is applied,the top of the old pile is deformed laterally toward the direction of the new pile,and the pile body and the pier body generate additional bending moments.As the distance between the new and old piles increases,the lateral additional effect and additional settlement of the old bridge due to new bridge load will decrease.(3)With the additional stress data derived from the FEM model calculation result,the creep deformation of the pile bottom soil can be calculated by the Mesri creep model.Using the measured data of the new pile settlement for a period of time,the back analysis determines some unknown parameters in the Mesri model.The model predicts that the settlement difference of the new pile after 5 years will reach 4.3mm,which is close to the 5 mm limit.;(4)According to the predicted development trend of differential settlement and the previous research on the allowable value of differential settlement,the differential settlement value between the old and new bridges was determined to be 5 mm.According to this value,the finite element model of T-shape girder bridge widening under different lateral connections is established,the stress and deformation of the splicing structure and the T-shape girder under different settlement conditions are analyzed.After the relative settlement of the new bridge occurs,the widening bridge under the strong rigid connection shows smoother deformation.The T-shape girders of the new bridge gradually sink from the side girder next to the connect joint to the outer girder,and the sinking curves of the girders in the horizontal direction is approximate the a secondary parabola.(5)After the differential settlement occurs between the new and old bridges,the joint stress of the widening bridge with strong rigid joints is the most disadvantageous.The tensile stress of the bridge connect joints with strong rigid connection may exceed the concrete limit,while the tensile stress and shear stress of the weak rigid connection are at a safe level.