Study On Pounding Effects Of An Irregular Multi-span Continuous Girder Bridge Under Transverse Earthquakes

The influences of retainers on bridge seismic responses are usually ignored in engineering practice.In recent years,researchers are increasingly concerned about the transverse pounding phenomena of bridge structures.However,most of the existing researches only focus on simple structures and do not take full consideration of retainers’characteristics.There is still a lack of good connections with studies on retainers’ mechanical properties.The following gradually thorough research works are carried out to explore the pounding effects of an irregular multi-span continuous bridge,for the purpose of having more realistic predictions of structural seismic responses and improving this type of bridge’s ability to withstand earthquake disasters.(1)The bridge’s analytical model for transverse pounding phenomena was established,taking the nonlinearity of its bearings and the pile-soil interactions into consideration.The characteristics of the transverse pounding and its effects on the seismic responses of the bridge structure were presented.A parametric analysis of the key factors was also conducted.The results show that the transverse pounding restrains the girder’s displacement,but the resulting pounding forces increase the piers’ internal forces and make the distribution of seismic forces more uneven among the piers.An increase in contact stiffness can improve retainers’ limit capability,but an excessive stiffness value will cause great internal forces in the piers.When the initial gap is smaller,the pounding forces and the piers’ internal forces are larger.(2)A new modeling method was proposed,which can simulate concrete retainers’characteristics and poundings between the girder and retainers.The effects of concrete retainers on structural seismic responses are investigated.The main parameters of concrete retainers’ characteristics were then analyzed.The results indicate that the retainers’ strength has a significant influence on their seismic performance.The relative displacements of the girder and the piers are smaller when the retainer’s strength is larger.However,an excessively large strength will greatly increase the piers’ internal forces.A better deformation capability of retainers makes pounding forces smaller and reduces shear keys’damages.A good limit effect cannot be satisfied by making the initial gap too small.(3)The mechanical simulative and analytical model of steel retainers is constructed.During the analysis of the transverse pounding effects of the bridge,the effects of steel retainers on structural seismic responses are inspected.A parametric analysis of steel retainers’ characteristics was then conducted.The results show that steel retainers’ seismic performance is mainly decided by their yield strength.Increasing the retainers’ yield strength can improve their limit capability.However,an excessive value of the yield strength will cause great internal forces in the piers.The retainers’ elastic stiffness has a similar but far less important influence than their yield strength.A too small initial gap does no good to the realization of the intended limit target.(4)The effects of different retainers were compared and their seismic performances were evaluated.The results indicate that ignoring the yield and failure of the retainers overestimates the retainers’ limit capability and the piers’ internal forces.The retainers’strength is the key to their displacement limit and force transmit mechanism.Elastic retainers are the case where the strength is too large.Their limit effect is ideal but they cause great internal forces in the piers.However,if the strength is too small,the retainers will be severely damaged and can hardly play the role of displacement limit.Steel retainers perform better than concrete retainers in restraining the girder’s displacement.(5)Rubber bumpers were taken as a pounding mitigation method.The mechanical analytical models of different types of retainers with rubber bumpers are proposed.Rubber bumpers’ effects on different types of retainers and the influences of the bumpers’ main design parameters are discussed.The results show that elastic retainers shall be equipped with rubber bumpers.Rubber bumpers significantly reduce the pounding forces and the internal forces in the piers.Concrete retainers should be equipped with rubber bumpers to further reduce relative displacements of the girder and piers and pounding forces,so as to mitigate shear keys’ damages.Steel retainers may also be equipped with rubber bumpers to improve their limit capability.It is suggested to increase the bumpers’ thickness appropriately,but the initial gap should not be filled up.