Experimental Study On Fatigue Performance Of Orthotropic Steel Bridge In Urban Rail Transit

In recent years,with the rapid development of rail transit,and a number of rail transit bridges have emerged.The main beam structures of large-span rail transit bridges are almost all in the form of steel structures.Most bridge decks use orthotropic steel bridge decks.The load of rail transit vehicles is unique,which is not only different from road vehicles,but also different from railways.Compared with road vehicles,the axle load is greater and the frequency of departure is higher than that of railways.At present,the research on orthotropic steel bridge decks is mostly focused on highway bridges and railway bridges,and there are few studies on rail traffic bridges.Therefore,it is very necessary to study the stress of orthotropic plates under the load of rail traffic.In this paper,based on the construction science and technology project of chongqing city,"research on transverse stiffness and steel box fatigue design of urban rail transit bridge".Firstly,the stress analysis of the orthotropic steel deck of the urban rail transit bridge is carried out,and then the fatigue test of the full-size model is carried out.The stress distribution and fatigue performance of the bridge deck and the connection position of the U rib,the connection position of the U rib and the diaphragm plate,and the opening position of the diaphragm plate under the load of the rail transit bridge are emphatically studied.The specific contents of the paper are as follows:(1)The axle load selection of rail vehicles is studied,and it is determined that the fatigue load factor of 0.8 is used as the standard fatigue axle load during the fatigue calculation,and the rationality of this factor is verified.Taking a rail transit bridge as a research background,a finite element model was established,and the stress on the parts of interest was analyzed in 13 working conditions to grasp the stress distribution characteristics of each part.The calculation results show that the bridge panel,u-rib and diaphragm plate are the most disadvantageous to be connected in two or three ways,and the stress concentration is easy to occur at the opening edge of diaphragm plate.(2)With reference to the structural form and finite element analysis results of the special bridge for a rail transit,a fatigue test model was designed,fatigue test research was conducted,and a finite element analysis was conducted for the test model.The test results show that when the external load cycle reaches the end of 3.25 million times,a crack occurs at the connection between the bridge deck and the U rib.When the external load cycle reaches the end of 3.5 million times,the crack is found in the first crack symmetry position.According to this suggestion,in actual engineering,the rails should not be arranged directly above the U ribs.(3)Based on the fatigue test results,the improvement measures were studied.By adding a U-ribbed internal partition to reduce the stress at the connection between the bridge deck and the U-rib,three types of internal partition layout were selected during the study.The calculation results show that the stress concentration of the bridge deck can be improved when the inner partition is connected to the bridge deck.