Near-filed Seismic Response And Seismic Isolation Analysis Of Diagonal Continuous Girder Bridge

The rapid development of China’s economy has gradually improved the transportation network,and skew bridges are increasingly widely used in the vast western region of China.In the western region,fault activity is frequent,and near fault ground motions often occur.Due to its unique structure,skew bridges are often subjected to more complex forces,and the bending moment coupling effect is stronger under earthquake action.The degree of damage in major earthquakes around the world far exceeds that of orthogonal bridges.In order to study the response law of skew bridges under seismic action,this article first analyzes the dynamic characteristics of skew beam bridges,explores the influence of skew angle,pier height,and whether pile soil interaction is considered on the dynamic characteristics of skew beam bridges.Secondly,it studies the influence of different skew angles and pier heights on the internal force at the pier bottom and displacement at the pier top under ordinary and near fault pulse seismic actions,Finally,by optimizing the parameters of five types of lead core rubber bearings that meet the design requirements,the bearing with the best seismic absorption rate is selected through analysis.This is used as a seismic isolation device to explore the impact of increasing pier height and oblique angle on the seismic absorption rate of bridge structures.To provide a reference basis for similar bridges,the specific research content is as follows:(1)Taking a skew continuous girder bridge in the west of China as the research background,the dynamic characteristics model of the structure is established by using the finite element analysis software Midas Civil,and the variation law of the vibration mode characteristics and natural vibration period of the bridge structure under the action of three key factors,including different skew angles,with or without pile soil interaction and pier height change,is considered.The research results show that the increase of the angle of the skew box girder bridge will change the frequency of the structure,Overall,there is a trend of decreasing with increasing angle,with the order of torsional deformation advancing and the degree of deformation increasing.The increase in pier height significantly reduces the frequency of the bridge structure,affecting the stiffness of the bridge piers.The degree of torsional deformation of the bridge piers increases significantly with the increase in pier height.This bridge type is a skew bridge with middle and lower spans.Because the height of the pile foundation is very low,resulting in a large stiffness of the structure itself,when considering the pile soil interaction,except for a slight difference in the frequency of the first order,the frequency ratio of the second order is close to one,so the impact of the pile soil interaction will not be considered in the subsequent research.(2)The effects of different angles and pier height changes of skew box girder bridge on the internal forces at the pier bottom under the action of ordinary ground motions and near fault pulse ground motions are studied by inputting the ground motions into the model along the bridge direction and across the bridge direction respectively.The results show that the bridge structure exhibits significant changes under both types of seismic actions.However,when subjected to near fault pulse ground motions,an increase in the angle of inclination will make the internal force form of the bridge more complex.The maximum difference in the internal force at the bottom of the transverse pier is much smaller than that in the longitudinal direction,making the structure more prone to damage in the longitudinal direction.When the pier height increases,the displacement of the pier top of the skew bridge also increases.If the lateral displacement of the pier top is greater than the longitudinal displacement,the lateral stiffness is less than the longitudinal stiffness,which is more likely to cause the beam to roll over.(3)Based on the actual situation of the bridge type,five types of lead core rubber bearings that meet the design requirements are selected according to the specifications for parameter optimization,and the bearing with the highest shock absorption rate is selected as the seismic isolation device of this bridge to explore the impact of changes in pier height and oblique angle on it.Research data shows that the post yield stiffness is the main influencing parameter of lead rubber bearings,and it shows a decreasing trend with the increase of post yield stiffness.The increase of pier height makes the bridge structure become flexible as a whole while reducing the shock absorption rate of lead rubber bearings.Therefore,this factor should be carefully considered when adopting skew box girder bridge with high piers.The increase in oblique angle will cause the shock absorption of lead rubber bearings to first increase and then decrease,and the shock absorption efficiency reaches its maximum at 30 °.The shock absorption rate is above 30%,which has good shock absorption effect and is suitable for various angles of skew bridges.