Dynaminc Response Analysis Of Shelijia Bridge Under Vehicle Moving Loads

Because of the economical cost,graceful shape and short build timescale,steel box tied arch bridges are widely built in China.But the dynamic vibration problem of this type of bridge is more prominent because of its light dead weight and small stiffness.In particular,the throughtype arch bridge’s suspender is too long,the integrity of the bridge is poor,and the live load is relatively large.In addition,the large number of structural systems of this bridge type makes the vibration mechanism under the vehicle moving loads more complicated.It is very necessary to study the dynamic performance of this type of bridge under moving vehicles.Base on the Shelijia Bridge,the spatial solid model is established,dynamic characteristics and modal parameters are analyzed.The equation of vehicle and bridge coupling vibration is established base on the modal synthesis method.,An analysis program is coded to solve the equation.An in-depth study of the dynamic performance of the bridge due to single-vehicle and multi-vehicles loads is performed.The local dynamic vibration of key components of through steel box tied arch bridge under vehicle moving loads are studied.The main research work and conclusions are as follows:(1)The spatial solid model of Shelijia bridge is modeled by ANSYS software.The three-axle truck was modeled as a three-dimensional,nine independent degree of freedom system.The displacement and impact factor of the bridge are obtained by numerical method and modal synthesis method,which reduces lots of calculation time.(2)The vibration mode of shelijia bridge is mainly manifested as arch rib out-of-plane vibration,in-plane vertical bending vibration,and spatial torsional vibration.The higher order,the more complex modal shape is.Coupled vibration such as torsional Deformation and arch rib transverse bending appears in the high-order mode.The first vibration modal shape of the bridge is the out plane modal with a frequency of 1.2237 Hz.The first vertical flexural modal shape of the bridge occurred in the second modal with a frequency of 1.3998 Hz.It means that the out of plane stiffness of shelijia bridge is less than its vertical flexural stiffness.Therefore,the problem of out plane stability of shelijia bridge must emphatically considered.(3)The influence of vehicular speed,road surface condition(RSC),lane position,vehicular weight,structure damping on the dynamic performance for shelijia bridge due to single moving vehicle is studied comprehensively.It is found that vehicular weight,structure damping,road surface condition(RSC)and vehicular speed have a great effect on the dynamic performance of shelijia bridge and lane position has less effect on that.The impact factor of the bridge is quite different in deflection and internal force.In some vehicular speed,the impact factor of the bridge is outweigh 0.05-which regulated by the Chinese design code.It is found that the existing design code underestimates the dynamic impact for this bridge.(4)The influence of vehicular speed,suspender connection model and RSC on the dynamic performance for the through steel box tied arch bridge due to single moving vehicle is studied comprehensively.The results are as follows: the internal force impact factor of some components are outweigh than the entirety impact factor.The impact effect of internal force on some key components is less affected by the suspender connection model.The local dynamic performance of bridge increases with the RSC degree,and some local components are more sensitive to the change of road roughness level.Therefore,it is unreasonable to use only one overall impact factor to reflect the dynamic performance of the bridge.The corresponding local impact factor should be selected according to the design needs and different research objects.(5)The influence of lane position,number of transverse loaded vehicles,vehicle driving direction,number of longitudinal loaded vehicles,RSC and vehicular distance on the dynamic performance for the through steel box tied arch bridge due to multi-vehicles is studied comprehensively.The results are as follows: number of transverse loaded vehicles,vehicle driving direction,the number of longitudinal loaded vehicles and RSC have a great influence on the dynamic performance of shelijia bridge.Lane position,vehicular distance has less influence on that.The single vehicle condition is most sensitive to changes in road surface condition level.In the multi-vehicles condition,the longitudinal multi-vehicle condition is more sensitive to changes in RSC level.The impact factor of the bridge under multi-vehicle load is less than the single vehicle condition.It is safe to select impact factor of the bridge under single vehicle condition for bridge design.