Preliminary Study On Impact Coefficient And Stiffness Index Of Long-span Suspension Bridge Based On Vehicle-bridge Coupling

The rationality of the load impact coefficient of highway vehicles is very important for bridge design.However,the impact coefficient specified by the current code is mainly for conventional span bridges and is used for the overall calculation of the structure.For the super-span bridges,due to the significant change of structural dynamic characteristics and the variability of the distribution of the bridge surface,the coupled vibration of the bridge The problem has a great influence on the local components of such bridges(such as stay cables and booms).At this time,the applicability of the impact coefficient specified by the current regulations needs further study.Bridge stiffness often plays a controlling role in the design of long-span track suspension bridges,and reasonable stiffness limit is a comprehensive problem involving engineering safety and economy: the stiffness is too low,it is difficult to ensure the safety of trains and Comfort;too high stiffness will greatly increase the difficulty of construction investment and construction.However,the existing regulations on the stiffness limit of rail bridges are mainly for medium and small span bridges,and are not suitable for long span track suspension bridges.The paper analyzes the impact coefficient and stiffness value of the public rail dualpurpose suspension bridge design based on the main girders of the steel truss main beam.Based on the existing theory of vehicle-bridge coupling analysis,the following aspects are completed:(1)The large-scale finite element software ANSYS was used to establish the shell element bridge deck and the equivalent beam bridge deck model respectively.The difference between the static and dynamic characteristics of the double-span suspension bridge under different modeling modes was studied.The bridge deck simulation method has no significant influence on the static and dynamic characteristics of the bridge.In the study of the coupled vibration of the axle of the double-deck suspension bridge,the equivalent beam can be used to simulate the bridge deck.(2)The displacement and internal force of the main members of the beam end,1/8,1/4,3/8,and 1/2 sections are taken as control items.According to the influence line loading,the most unfavorable fleet layout corresponding to each control item is calculated.The most unfavorable fleet layout was loaded on the bridge deck,and the dynamic response of the bridge under the uneven road conditions of A,B and C was carried out.The results show that the road surface roughness is an important factor affecting the coupled vibration of the axle.The coupling vibration of the axle system will be more severe with the unevenness of the road surface,and the impact of the vehicle on the whole and the part of the bridge is more obvious.(3)The impact coefficient of 91 projects focused on double-deck suspension bridges under the most unfavourable fleet layout was carried out.The results show that the standard impact coefficient value of 1.05 can not envelop the local impact coefficient of the bridge;the local impact coefficient of the boom is negatively correlated with the length of the boom;the internal force impact coefficient is significantly larger than the displacement impact coefficient;the impact coefficient of different parts is different,and the parts are The impact coefficient is not the same for the unevenness of the road surface.When the A-level pavement is uneven,the maximum displacement coefficient of the bridge is 1.215.The maximum impact coefficient of the internal force of the main beam is 1.13,the maximum impact coefficient of the axial force of the boom is 1.077,and the impact coefficient of the internal force of the cable is less than 1.57.1.05,the bottom axial force and the vertical bending moment impact coefficient are all less than 1.05.Based on the measured data,the local impact coefficient of 1.23 can completely envelop all the displacement and internal force impact coefficients.(4)The influence of bridge member stiffness on structural dynamic characteristics,the sensitivity analysis of bridge coupling response and the detailed analysis of stiffness performance are carried out.The main frequency range of the power spectrum of flexible long-span suspension bridge due to the main frequency away from vehicle vibration is obtained.The conclusion that the bridge stiffness has no obvious influence on the train vibration response is of great significance for further research on the reasonable stiffness limit of long-span rail transit bridges.