Research On Vehicle-induced Vibration Response Of The Wide Steel Girder Bridge

In order to solve the increasing congestion condition of the urban traffic,the width of steel box beams are increasing constantly.This kind of bridge structure has the characteristics of large width-span ratio,central bracing,less deadweight,and so on,for such structure: on the one hand,due to the large width-span ratio and central bracing,the spatial effect of bridge will be remark,the torsional modal contribution to the vertical vibration response of the structure also will significantly increase,especially when traffic jam occurs or several overloaded trucks travel on one side of the bridge will cause serious offset load effect,even endanger the safety of the bridge.On the other hand,due to less deadweight,the large mass ratio of vehicle to bridge,small damping ratio,coupling vibration effect of vehicle-bridge will be significant and attenuates slowly.Therefore,it is very meaningful to study the vibration of this kind of bridge.Based on one wide steel box beams under construction,the main work in this paper is as followed:(1)A sophisticated 3-D finite element model is presented for wide steel box-girder bridge,the second order response surface method based on dynamic characteristics obtained from the field ambient vibration is adopted to updating the FEM,the influence of the paving,equivalent masses of adjacent bridges,the stiffness of longitudinal joints,safety barrier to bridge’s natural frequencies are discussed.(2)Vehicle-bridge coupling vibration analysis model is established,the solving program is programmed using ANSYS and FORTRAN.(3)The impact coefficient under design load of wide steel box girder bridge is discussed using the solving program,the influence of partial load distance,speed,road roughness,damping ratio of bridge to dynamic response of the bridge are discussed,the contribution of torsional mode to vertical dynamic response is analyzed.Through the above work,the following conclusions are drawn:(1)The FEM prosed by this paper is quite accurate,the paving will lead to the huge decrease of natural frequency,equivalent masses of adjacent bridges have significant effect on the lateral and torsional frequencies,safety barrier have finite effect on the natural frequency,the longitudinal expansion joints have significant effects on bridge longitudinal mode only.(2)The inhomogeneity in the transverse direction of the impact is presented,when calculating the impact coefficient,approximately equal to design load should be adopted,employing the outside lane on the partial load side;the road roughness,the damping ratio of bridge,the distance of partial load have significant influence on the dynamic response of bridge.As the distance of partial load increases gradually,torsion modal contribution to the vertical dynamic response increases gradually,even more than the contribution of the first order vertical bending mode.