Structural Behavior Of The Road Diaphragm Of Continuous Truss Of Rail-cum-road Bridge

The steel truss girder of rail-cum-road bridge has many advantages,such as light weight,high stiffness,strong bearing capacity,full use of natural resources,saving money and strong span ability.In our country,many of the rail-cum-road bridges are built after the founding of the people's Republic of China.The related technologies in the early stage of the design and construction are not yet mature,and there is no specific code for the rail-cum-road bridge.With the rapid development of economic construction,the traffic volume of the bridge is increasing rapidly and the number of heavy vehicles is increasing abruptly.There are many problems to be solved urgently.In this paper,the structural characteristics and the stress performance of the rail-cum-road bridge are mainly studied,which provide valuable experiences for the design and construction of the similar bridges in the future.This thesis mainly introduces the development situation,development trend and calculation method of the steel truss girder of rail-cum-road bridge around the world.Taking a five span continuous steel truss girder of rail-cum-road bridge as the engineering background,the finite element software Midas/ Civil is used to establish the whole bridge unit model,and the whole structure of the bridge is simulated and analyzed.On the basis of whole bridge analysis,the local finite element model of the highway bridge deck system and its subsidiary structure is established on the basis of the whole bridge analysis,and the boundary situation of the whole analysis is applied to the local finite element model.The mechanical properties of the steel beam under various main conditions are analyzed.The thesis first calculated the displacement and stress conditions of steel crossbeam,steel longitudinal beam and its subsidiary structure,and the support of the block on the flange of the steel beam under the constant load,the most unfavorable load of the vehicle,the load combination and overloading.The calculation and analysis show that under the action of dead load,the displacement on both sides of the flange and the counterforce of the cushion are equivalent,and there is no torsion deformation.The vertical displacement difference and the longitudinal displacement difference on both sides of the end cross beam flange are large under the most unfavorable load of the end cross beam.The side beam of the end cross beam has a serious partial load effect,which causes the steel transverse beam to twist to the vehicle load side,and forms the stress set middle point at the stiffening rib of the steel crossbeam web,which leads to the repeated load.Fatigue cracking,while the middle beam partial load effect is not obvious,will not produce larger torsion deformation.Then,the stress situation of the end cross beam and the middle beam under the load combination and overload is analyzed.The calculation results show that the stress concentration of the end cross beam is serious under normal operating conditions;the overloading effect makes the peak of the stress concentration area increase and accelerates the appearance of fatigue crack.According to the time stress cycle curve of the vulnerable point,the crack disease of the tapping beam is caused by fatigue,which is based on the time stress cycle curve of the vulnerable point.Finally,according to the calculation result and the cause of disease,the transformation plan is put forward,and the rationality of the retrofit plan is analysed and discussed through the improvement of stress and fatigue.