Structure Optimization Of The Spatial Truss Compound Girder Bridge Made Of Steel Pipe Concrete

With the fast development of economic in recent two decades, long-span bridges spring up, the concrete structure's application is restricted in long-span bridges because of its big weight,easy to crack, and need higher-cost formwork supports. Concrete filled steel tube structure is characteristic of good bearing capacity, good ductility and toughness, anti-seismic capability and easy construction which fully combines steel's tensile performance and concrete's compressive performance characteristics. Spatial truss structure of concrete filled steel tube is a new structure type and been commonly used for bridge which is progress from traditional box girders bridges, and possess both the light weight high strength material-concrete filled steel tube-and most advantages of box girders, furthermore get rid of the disadvantage. However, this brand new structural form's force-analysis is complex so there is no unified design construction standard, design and construction works are been exploring, problems should be proving and optimizing so as to form a unified standard.In this paper, taking a Space truss girder bridge concrete filled steel tube in Sichuan province for the engineering background, based on domestic and external researches, optimize the design and construction of Spatial truss structure of concrete filled steel tube. The main research contents of paper are as follows:(1) Build four models with deferent pouring length of concrete in lower tube by ANSYS, and analyses the impact of concrete pouring length act on the structural displacement and local stress distribution under static loading, witch including four cases:only gravity, distributed load fully loaded bridge deck, and eccentric load loaded on the lateral lanes of the left half bridge or the right. Analysis the overall stability and local stability of structure by buckling calculation, analysis the maximum displacement and the greatest stress of structure. Through comprehensive contrast, optimal concrete pouring length in lower tube is 1/3 span.(2)Using birth-death element analysis technology in the optimal ANSYS model above, simulate eight different pouring sequences of lower tube, upside tube and bridge deck, by comparing structural displacements and local stresses of eight deferent construction conditions, it can work out the optimal pouring sequence:firstly concrete in lower tube, then higher, secondly concrete of bridge deck in the bearing span -1/2 span-and then mid-span which is also 1/2 span.(3) Analysis and calculation from the above provide guidance to construction of this project, and provide reference for design and construction of other similar structure form of bridge.