| Try using ultra-high performance concrete (UHPC) in girder bridge, taking fulladvantage of its high material strength, excellent durability and ultra-low shrinkageand creep performance, and designing new form of bridge structure, in order toachieve lighter structure and solve the problems that conventional concrete girderbridge usually faced, such as the too big dead-weight, the excessive long-termdeflection in the centre span, easy cracking, and hard to break300m span. The salientfeature of the new structure is its comprehensive thin-walled box girder, meanwhileintensive diaphragm plates is proposed to diminishing deterioration of the distortionand shear lag effect caused by comprehensive reduction of plates, and also improvingthe transverse force of the box girder and only setting longitudinal prestressing so asto facilitate the construction. Intending a engineering background with the400m mainspan continuous girder bridge, and research the reasonable value of the bridgeparameters (side span ratio, height of the beam, plates thickness, parameters of theintensive diaphragm plates and so on) by optimal design. The main research carriedout in the thesis and its conclusions as follows:(1) Building the beam element model by using the MIDAS software to simulatethe continuous thin girder bridge with main span400m, and optimize the overallparameter of the bridge, such as side span ratio, the height of the beam, platesthickness, prestressed reinforcement. Based on the influence degree of the parametersto the overall performance of the bridge and their own characteristics, the relativelyappropriate objective function and constraints is selected to optimize the bridgerespectively, and the latter parameter optimal analysis is on the basis of the result ofthe preceding optimization.After a series of optimization analysis can be obtained:①the best optimal ratioof side to main span is0.6, and reasonable ranges from0.55~0.65;②the bestoptimal ratio of fulcrum section height to the main span is1/22.2, reasonable rangesfrom1/20~1/25;③the best optimal ratio of center section height to fulcrum sectionheight is1/1.8077, and reasonable ranges from1/1.8~1/2.3;④the best optimal ratioof the fulcrum bottom thickness to the main span is1/500, and reasonable ranges from1/300~1/500;⑤reasonable thicknesses of the roof plate, the center bottom plate andthe center web plate is the minimum20cm restricted to construction, and thereasonable thickness of the fulcrum web is35cm. (2) The long-term deflection growth is suggested to be1.3, while designing thenew type UHPC girder bridge after the preliminary analysis of creep performance, andthe thickness of the fulcrum bottom is not recommended for too small, whileconsidering the circumstances that it is affect the long-term deflection to a greatextent.(3) Building solid model of the half-bridge by using finite element analysissoftware—ANSYS, and the intensive diaphragm is optimized through two steps: thespacing of the intensive diaphragm and the height of upper diaphragm, bottomdiaphragm and the width of side diaphragm. In order to obtain optimum spacing rangeof the diaphragm plate, Comprehensive analysis of the impact is conducted on howthe spacing of the diaphragm plate affect the distortion, the shear lag effect and thelocal stress of the bridge deck. The optimization on the size of the intensivediaphragm is considered for the contribution that reasonable size distributionameliorate the local stress of the bridge. Optimized analysis diaphragm plate getoptimum spacing ranges3~5m; The top heights and the thickness of the diaphragmplate should be appropriate increase when distribute its size, in order to improve themechanical state of the local box girder bridge. |
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