Mechanical Analysis Of High Speed Railway Bridge With Long Span And Three Main Trusses

Research of transverse distribution of internal forces i of great importance in studying characteristics of high-speed railway bridge with three main trusses, and optimization analysis method is an effective way to improve research efficience for long span bridge with three main trusses. Some achievements listed as bellow have obtained in this dissertation:(1) Transverse distribution of internal forcesWith the method of frame analysis, formula for calculating vertical displacement difference on steel truss bridge with two main trusses, have been derived. The vertical displacement difference on steel truss bridge with three main trusses acting by offset load can be calculated by the formula of girder with with double chamberes in its box section, and on the acting of full load, the formula of girder with with one chamber in its box section can be referenced. The transverse distribution of internal forces in bridge with three main trusses is much more complex than that in bridge with two main trusses.Results obtained from FEM show that transverse distribution of internal forces and transverse displacement coordination in arch bridge with three main trusses lie on the stiffness of cross linking system, so keeping the nodes of floor beam fixed is a guarantee to the stiffness of cross linking system. Truss arch bridge can also get better displacement coordination among three trusses by adjusting the tension of hanger rod.Cable tension plays a key role in keeping displacement coordination among three trusses in cable-stayed bridge with three main trusses. The best bridge cable tension, which makes maximum rotational angle of section under various loads can meet demand, is analized by cable tension function method and frame analysis method.(2) Analizing model of five-span continuous beamTo a seven-span continuous beam with length of 120m+5×168m+120m, although the difference between the spans is more than 28 percent, the calculating results show that the seven-span beam can be analized by the modeled of five-span continuous beam (120m+3×168m+120m).(3) Analysis of the deckTo the deck with opening rib and stringer, inneral forces of the main beam are very close to each other in three analysizing models: plate element model, beam element model, and larger size beam element model. Both the stress value and its distribution of deck occur with same features in the three models. All of those show that the deck with opening rib and stringer can be analysized by submodel.To the deck with large closed rib, inneral forces of the main beam are very different in two analysizing models: plate element model, plate and beam element model. It inferrs that the deck with large closed rib should analized by plate element model. To structure with many same parts, it can be studied by substructure FEM.(4) Spatial analysis modelFrom energy point of view, the ratio of of moment energy and force energy is studied. Studied results show the moment energy in most bars can be negected, that is to say, the majority of bars can be modeled by link element instead of beam element. This model can reduce the total number of degrees of freedom and shorten the calculating time.(5) Automation of calculationA fast calculation method for the influence line of railway bridge as well as method for statement generated automatically by computers are given in the dissertation to reducing the workforce and improve work efficiency.(6) Analysis of foundationThe Semi-analytical and semi-numerical (SASN) method has a high efficiency in analizing foundation. The fundamental solution of soil in SASN method can be easily obtained by axisymmetric FEM. Axisymmetric FEM is a kind of 2D algorithm with many advantages as numerical method does, so it can be used to impove the efficiency of studying the fundamental solution of layered soil by existing commercial FEM software.The work of this dissertation can be used for the engineering design of Nanjing Dashengguan Yangtze River Bridge and Zhengzhou Yellow River Bridge, but also as reference for the mechanics analysis of bridge with three main trusses.