Study On Full Loading Process Performance Of Simply Supported Continuous P.C. Multi-box Bridge

Simply supported continuous P.C. multi-box bridges are widely used nowadays. With the development of science and the improvement of the suspend capacity, there has been a noticeable trend in the enlargement of span range and the standardization of medium and small-span bridge design. But the test researches and the whole loading process analysis on the simply supported continuous P.C. multi-box bridges both inland and overseas are relatively laggard, which has stunted the healthy development of this type of bridge badly. According to the item of "Analysis and Experimental Study on the Mechanical Behavior of P.C. Multi-box Girder Bridge" which is a science and technology project item of Ministry of Communications, Zhejiang Province, detailed test analysis and theoretic research are done. And the primary achievements are listed as follows.1) Polymethyl methacrylate structural model test is done, focusing on simply supported continuous P.C. multi-box bridges, and the applicability and the exactitude of the solid degenerated virtual laminated element theory and program are verified.2) The Pre-stress spatial effect calculation method based on virtual laminated element is researched. Then a 5 X 25m multi-box girder bridge in the highways is adopted as the engineering antitype, and its mechanical behavior is analyzed for the whole process from the construction stage to the finish state. The spatial effect of a single box and the workability changes because of transverse connections are discussed in detail. The results show that the side girder put up apparent spatial stress distribution because of free torsion, and the transverse and the lognitudinal link of the girders can reduce the effects to some degree. No spatial effect such as shear lag effect exists except for free torsion.3) To the simply supported-continuous construction techniques bifurcation about the sequences of post-connection concrete cast, the pre-stress wires tension and the temporary support removal, the stress and displacement of the key points in different construction sequences are fetched with the FE model constructed with virtual laminated element, then a most rational construction sequence is put up.4) Based on present 3-demension solid degenerated virtual laminated element program, the non-uniform hardening plastic relationship of Ottenson 4-parameter failure criterion is deducted and the material muster of the program is enlarged; the live-dead blocks technique is developed for pre-stress wires based on the construction characteristics of the USAP model, which expands its applicable extension. A standard designed 5 X 25m multi-box girder bridge in the highways is adopted as the engineering antitype, the ultimate loading capacity in various loading cases are calculated. The safety of the structure with different numbers of spans is investigated; the mechanical behavior changes and the load transverse distribution coefficient changes in increasing loadings are discussed; the force re-distribute disciplinarian when the structure is in plastic stage and the influence of middle diaphragm are discussed. Besides, the influence of some design parameters such as pre-stress degree, pre-stress amounts, hoop steel areas, bottom plate steels area, upper plate depth, bottom plate depth and web depth on the ultimate loading capacity of the bridge is analyzed. Some useful conclusions are made based on the ultimate loading, failure characteristics, displacement-load diagrams and safety coefficients calculated, etc, which also provide the theoretical foundation for the optimization of the structure design.