Study On The Effects Of The Structural Damage On The Mechanical Properties Of The Long-span Railway Steel-concrete Composite Trussed Beam Bridge

Steel-concrete composite trussed beam bridge is a bridge structure developed on thebasis of the ordinary combinations beam bridge, which can give full play to the performanceof the material, and is suitable for large span and heavy load structure. In the recent forty orfifty years, because of the good performance in force and its economic condition,combinations beam bridge has been paid more attention by the designers. The maximum spanof the bridge of this type in the world before is51.8m. There are three cross high-speed bridgemade of steel-concrete composite truss bridge of the railway from Xian to Pingliang inChina. The span of the bridge is80meters, which is currently the world’s largest span. Such alarge-span steel-concrete composite truss bridge is built for the first time in China and evenin the world. Therefore, the researches from all the aspects on such type of bridge arevacancies. Taking80m steel-concrete composite truss bridge as engineering background,this paper studies the possible damage of the bridge, and makes an analysis on the changes offorce performance of the damaged bridge by producing the damage models. The main contentconsists of the following parts:(1) Make an analysis on the major external factors that cause the damage of the steel-concrete composite truss bridge. The main damage part is the junction of the node concreteand the steel webs. The damage of such bridges is caused under such external conditions asenvironmental corrosion, train load and temperature effect.(2) Make an analysis on the damage mechanism of the steel-concrete structure. Calculateand analyze the main complex stress distribution area of combining nodes by establishing thenon-linear stress model of steel-concrete composite node. Make a simulating analysis on thedamage process of nodes, and study the development of the nodes as well as the process ofthe stress changes. Based on the above-mentioned study, analyze the damage mechanism ofsteel-concrete composite structure.(3) Make an analysis on the theories and models of the steel-concrete structure. Theassumption of Mazars’s theory is the initial damage that doesn’t exist, while the Lolandmodel and the assumption of the piecewise linear theory are the existing initial damage. Thestress and strain as well as the relative curve between damage and strain are separately given.Analyze and study the integrated theory of virtual crack (FCM) and damage theory.(4) Make a study on the effects of the structural damage on the mechanical properties ofsteel-concrete composite truss bridge. Firstly, analyze and study the value simulation of thedamage structure. Secondly, make an analysis and study on the changes of bridge mechanicalproperties after damaging the bridge structure by establishing the analyzing model of thefinite element damage of the whole bridge. Respectively analyze the static performance from such three aspects as girder cross-section stress, girder cross-section deflection and websstress changes. Use these two dynamic characteristics--the natural frequencies and modeshapes of the structure as an indicator to make a structural dynamic performance. Thirdly,make an analysis and study on the effect of the adjacent nodes after damaging the nodes, andcalculate by establishing separately the model that ventral rod is considered and the modelthat ventral rod is not considered. The result shows that using ventral rod to transfer energydoes have an affect on other nodes after damaging the nodes.