Displacement Response And Vibration Reduction Of Large Span Suspension Bridge Based On Random Traffic Flow

There are more than 30 suspension bridges with a span of over 1,000 meters in China,and the construction of long-span suspension bridges is still booming.As an indispensable key component of long-span suspension bridges,large-scale expansion joint devices are expensive,and their design specifications are closely related to the amount of expansion and contraction.For the design of expansion joint,the vehicle load accounts for an important part.At present,the calculation of this part is still considered according to the highway I-level load,which leads to the design of the expansion joint size being too large,which directly increases the overall cost of the bridge.In addition,health monitoring data shows that the expansion joints have major diseases during the operation process,resulting in many later maintenance costs.The premature failure of the expansion joint is closely related to the massive cumulative displacement of the girder end,and the repeated action and impact of the vehicle load are the key factors causing the massive cumulative displacement.Therefore,the study of girder end displacement based on random traffic flow has essential engineering significance for reducing the specification of expansion joints and improving their durability.With a long-span bridge taken as an example,the girder end displacement response and vibration reduction measures are systematically studied based on random traffic loads.The main research contents and conclusions are as follows:(1)According to the measured traffic flow data of a large-span bridge,a statistical analysis is carried out on the proportion of traffic flow in each lane,the proportion of vehicle types in each lane,the vehicle weight of each vehicle type,the distribution ratio of the axle load of each vehicle type,and the longitudinal spacing of vehicles.The results show that the vehicle weight obeys the Gaussian mixture distribution,the axle weight distribution ratio obeys the normal distribution,and the vehicle spacing obeys the log-normal distribution.Furthermore,the corresponding distribution model parameters of the vehicle weight,the axle weight ratio,and the longitudinal vehicle spacing are further given.After that,based on the Monte Carlo method,a random traffic load simulation program is compiled with MATLAB,which provided the analysis basis for the subsequent research.(2)With a long-span suspension bridge taken as the engineering background,the structure’s natural vibration characteristics are first analyzed.And then combined with the random traffic load program,the girder end displacement under the random traffic load for a month is calculated based on the principle of influence line loading.Taking the 30-day result as the basic data of unit time,the extreme value of the girder end displacement under different return periods is obtained by the extreme value extrapolation method of the Rice formula.The results show that the girder end displacement obtained by extreme value extrapolation method is only 50% of the code calculating value.Using Combin40 elements to simulate the longitudinal limit bearing,the finite element model of longitudinal limit constraint is established.For safety considerations,the highway I-level load is adopted to calculate the longitudinal limit force under different limit gaps,which provides a basis for reasonably reducing the design amount of expansion joints.The results show that with the extrapolated extreme value and the longitudinal limit,the design amount of expansion joint under temperature and vehicle load can be reduced by about 30%,and the limit force is about2700 k N.(3)Using the transient analysis function of ANSYS,the dynamic displacement response of the girder end under the longitudinal floating system is studied.And the results show that the cumulative daily longitudinal displacement of girder ends can be as high as 500 meters without longitudinal restraint.The finite element models of three different vibration reduction measures,including viscous damper,central buckle,and cable setting between tower and main cable are established.After that,the corresponding vibration reduction measures’ parameter sensitivity and optimization analysis are carried out.The results show that the damper has an excellent vibration reduction effect on the longitudinal displacement of the girder end,followed by the vibration reduction effect of the cable setting between tower and main cable and the central buckle.In terms of vibration reduction effect,dampers should be used in combination with cable setting between tower and main cable,and dampers should not be used in combination with central buckles.