Study On The Effect Of Side Retainers On The Seismic Isolation Effect Of Continuous Girder Bridge With Rubber Bearings

In China,small-to-medium-span simply supported beam bridges or continuous beam bridges play an extremely important role in road transport systems.Such bridges used plate rubber bearings and reinforced concrete retainers are placed on the piers and tables to form the anti-seismic system of the upper structure,generally.In this paper,based on the background of earthquake damages such as reinforced concrete block failure,bearing damage and falling beams,which are commonly seen in the WenChuan earthquake,three typical bridge with different pier heights are selected.and double rubber plates are considered.A non-linear three-dimensional analysis model with the bilinear constitutive model of the plate rubber bearing and the reinforced concrete retainers constitutive model is established.The strength of the retainers(the percentage of the dead load reaction at each pier),the deformation ability of the retainers,and the initial gap between the retainers and the main grider are analyzed using parameters.And the resulting lateral displacement response characteristics of the superstructure of the bridge and the internal force response variation of the substructure.Finally,the IDA analysis method was used to analyze the IDA curve characteristics of pier column curvature parameters,pier column shear parameters and bearing maximum deformation parameters.Vulnerability of the bridge key components and bridge systems was also studied.The main research conclusions are:(1)The three bridges adopted the single-short pier structure(Bridge HSH),the double-short pier structure(Bridge HSH),and the full-short pier structure(Bridge SSS).Studies have shown that different pier height determine the lateral stiffness distribution of the bridge.Therefore,the force of the high-pier and the short-pier in each bridge is different and the force of the short-pier is obviously more unfavorable.The deformation of the short-pier and the internal force of the pier are larger than those of the high-pier.The probability of surviving the same degree of damage of the short-pier and the bearings supported on is greater than that of the high-pier.(2)With the increase of the strength of the retainers,the lateral stiffness of the bridge increases,the retainers can significantly reduce the lateral deformation of the bearing and the lateral displacement of the main grider,and play a limiting role.At the same time,the retainers can also transmit more inertial force of the main grider to the pier column,the shear force of the pier bottom and the curvature of the pier bottom section continuously increase.Parametric analysis shows that the strength of the retainers is the most important factor in controlling the yield of the pier and determines the yield of the pier.In general,on the one hand,the 30% strength retainers can control the deformation of the bearings,so that it does not occur serious destruction,on the other hand,it will not excessively increase the seismic internal force of the pier.(3)Base on the 30% strength of retainers,with the increase of the deformation capacity of the retainers,the bearing deformation,the main grider displacement,the shear force and curvature response of the pier are increasing with small increment;when the deformation of the retainers is sufficient large to not destroyed in the earthquake,although the retainers restricts the sliding of the main grider,the large deformation of the retainers at this time can not decrease the deformation of the bearing,the shear force and the curvature response of the pier.In general,when the strength of the retainers is determined,the deformation capacity of the retainers has little effect on the seismic response of the bearing deformation,the main grider displacement,the shear force and curvature of the pier,and can only have a small impact.When the retainers deformation capacity is 0.15 m,the overall seismic response of the bridge is minimal.(4)Base on the 30% strength of retainers,with the increase of the gap between the retainers and the main grider,the free sliding space of the main grider is increasing,which directly leads to the increment of the displacement of the main grider and the deformation of the bearing,and the shear force at each piers bottom was reduced slightly,and the curvature at the each pier bottom was also reduced to a certain extent,but overall the decline was small.Therefore,under the condition that the strength of the retainers is determined,the change of the retainers-gap has little effect on the seismic response of the bearing deformation,the main grider displacement,and the shear strength and curvature of the pier,and the bridge earthquake can be affected by the variation of the gap parameter of the retainers.The seismic response is optimized,and the best results are obtained when the retainers-gap is 0.02 m.(5)On the basis of 30% strength of retainers,the friction force between the main grider and the bearing increases with the increase of the friction coefficient of the plate rubber bearing,and the lateral deformation of the bearing and the lateral slip of the main grider are thus obtained to a certain extent control.And when the friction coefficient exceeds a certain range,the change of bearing friction coefficient has little effect on changing the bearing deformation and the main grider displacement.Because of the damage of the bearings and the retainers on the short-pier,and those of the high-pier is basically in the elastic state.Therefore,the process of increasing the friction coefficient is essentially the process that the short-pier and the high-pier transmit the increased friction force to the pier.In general,under the condition that the strength of the retainers is determined,the change of the friction coefficient has little effect on the seismic response of the bearing deformation,the main grider displacement,and the pier column shear force and curvature.(6)With the increase of ground motion PGA,the pier bottom section curvature and yield degree of the piers are increasing,but the increase in yield is small.And the maximum deformation of the bearing is increasing,and the shear resistance parameters of the pier are increasing with a large rate before the retainers were destroyed,and the increasing after the damage was small.(7)For 30% strength of the retainers,the retainers on the high-pier is still in normal operation when it is at a PGA = 1.0g;and when it is on the short-pier and PGA = 0.6g,the retainers is basically completely destroyed.The results is that no damage to all the bearings on the high pier at each PGA,and the bearings on the short-pier does not breakdown within 0.4g of the PGA,and slight damage occurs at 0.7g.(8)In the seismic vulnerability analysis of typical components,with the increase of PGA,the probability of surpassing the damage state of each pier and the surpassing probability of the damage state of each bearing are increasing.And in the same ground motion intensity,the probability of occurrence of a low-grade damage state is greater.With the development of the damaged state of the piers and supports,the state of damage gradually increases,but the probability tends to be gradual.In the vulnerability analysis of the bridge structure,with the increase of the PGA,the probability of surviving the damage state of the system is increasing;although there are differences in the surpassing probability of different damage states among the components,the differences between the individuals have an effect on the overall system of the bridge.The influence of the damage state beyond the probability is small,and the bridge system is more prone to damage than any other component.