Research On Dynamic Response Of Military Beam Temporary Cover System Under Vehicle Load

When subway stations are under construction in busy traffic areas,in order to meet the needs of construction and ensure the traffic capacity of important traffic sections,half-cover excavation methods are often used as the construction method as a temporary cover system for the upper part of the envelope structure.The stability under the action is related to the overall safety of subway station construction.In this paper,the stability of the military beam temporary bedding system in the semi-cover excavation construction method under the action of automobile load is studied from the following aspects:(1)Use the 941 b vibration pickup and COINV acquisition instrument to conduct on-site measurements of the vibration of the temporary bedding system under the action of driving,and then perform software analysis on the collected vibration frequency to obtain the impact coefficient and the impact coefficient of the temporary bedding system under the test.(2)Use Midas civil software to model the temporary bedding system,analyze the load on it,and calculate the displacement,internal force and stress of the road slab and the 64-type military beam under the static force of the temporary bedding system The change shows that the military beam temporary bedding system meets the bearing capacity requirements under load.The upper chord is the largest in terms of internal force,and the middle-span and lower chord is the largest in terms of stress.(3)The modal analysis of the temporary bedding system using Midas civil software shows that the error between the natural frequency of the finite element model and the measured natural frequency is within the allowable range,and the first-order natural frequency of the military beam temporary bedding system is2.74063.The natural vibration frequency is low,which indicates that the overall structural rigidity of the temporary bedding system is relatively weak,so it is necessary to conduct a dynamic response analysis.In addition,the continuous variation of the frequency of the military beam temporary bedding system is small,the changes are uniform and the distribution is relatively dense,so the dynamic characteristics of the temporary bedding system can be obtained is more complicated,and the high-order mode shape needs to be considered when calculating the structure.influences.(4)The time history analysis of the finite element model of the temporary bedding system is carried out,and the influence of different vehicle speeds and road unevenness on the stability of the temporary bedding system is analyzed.It is obtained that within a certain range,the vertical displacement of the mid-span node increases with the increase of vehicle speed.Increase.The maximum vertical acceleration increases with the increase of vehicle speed,reaching the maximum value at 100km/h,but the vertical acceleration amplitude decreases after 100km/h.This is because the faster the moving load,the shorter the load on the temporary bedding system,the lower the interaction between the vehicle-bridge vibration and the lower the vertical acceleration,so it is necessary to limit the speed of the vehicles driving on it.Regulations.At the same time,the time history analysis of the dynamic displacement of the mid-span node when the car is running at 40km/h on different road levels shows that with the continuous decrease of the road level,the maximum dynamic displacement of the mid-span node gradually increases,and the road level becomes worse.The more frequent the vibration of the temporary covering system of military beams caused by the driving of the automobile.