The Theoretical Analysis Of Space Truss On Torsion Limit Bearing Capacity Of Twin-Cell Box Girde

At this stage, The application of bridge in engineering is more and more widely, from the form of the cross section of the bridge, As its good torsional bearing capacity and flexural tensile of box girder bridge, and its integrity and so relatively strong to adapt to a variety of situations of construction, so the box girder bridge is more and more application to factual bridge construction. This paper studies under the Natural Science Foundation of China which are Space Mechanics and Finite Segment Method of Thin-Walled Multi-cell Box Girders, and combined with the model test and numerical simulation, focuses on several questions in theoretical analysis in thin-walled twin-cell box girders, the main research contents followed:(1) For the thin-walled twin-cell box girders under the effect of external torque, using closed form analysis method to analyze the shear flow of the chamber and top floor and each web torsional, get the conclusion bellow: under the external torque,the shear stream of each plate is different in multi-cell box girder. For double-cell box girder, the shear stream of the medium web is about 7% of the floor, the medium web plays a relative small role than the side web in the resistance of external torque in twin-cell box beam. Therefore, it can be considered that in the resistance to the external torque of the twin-cell box girder, the main resistance is the whole section of the box beam.(2) Compared with single-cell box girder, the concrete plastic resistant of the twin-cell box girder changes due to the presence of the web, with the approximation of the torsion center of of twin-cell box girder, the concrete plastic resistance of twin-cell box girder is concluded.(3) According to the theory of truss, when the box girder is cracked, the concrete and the steel bar combined with together to resist the external force and torque. As the web plays a little role than that of the top, bottom plate and side plate of the box girder in the process of anti torsion, then when the box girder cracked, the effect is like single-cell box girder. As the medium web does not participate in the truss system, so the reinforced coefficient of the calculation formula of torsional bearing capacity of two-room box girder is adopted in the code of highway given 1.2. As the change of the plastic resistance moment of cross section concrete, the coefficient of the concrete needs to be revised.For the design of reinforced in concrete box girder under torsion, the present method is is the method of More and More Recognized. In this paper, the theory of softened truss is used to deduce, collect and organize the relevant formulas of the reinforcement process. As to test the the calculation of the design flow, using MATLAB to prepare the calculation program, and then through the example, the calculation formula of the coefficient of concrete of the single-walled twin-cell box girder is drawn. At the same time, torsional bearing capacity calculation formula of the single-walled twin-cell are for highway bridges, then for the railway, it can also be obtained by the strength conversion of the steel bar and the concrete.(4) This paper focuses on the single-walled twin-cell box girder, puts forward the vertical bending and local torsion combined deformation mode of a single-walled twin-cell box girder under symmetrical vertical load according to the section equivalent load. The equivalent load and the formula of the local torsion effect are obtained based on the equilibrium of the shear flow of the section, Then through the comparison of the results of numerical simulation and model test of twin-cell box girder, verify the correction of the calculation formula of partial torsion effect presented in this paper, analyzed the local torsional rules of the single-walled twin-cell box girder.(5) For the current standard of railway 32 m single box double room simply supported beam bridge, when the double track train live load effect in box girder of two side webs roof near the side webs and a cantilever plate parts and the stress of the elementary beam calculation stress sign consistency, and far away from the load of the bilge plate stress and elementary beam calculation should force of opposite sign. The local torsional stress distribution and the l/4 cross section of the cross section are different along the direction of the beam length. The top and bottom plate are in close proximity to the web, which is the compressive stress, the side plate and the cantilever plate.(6) For the existing railway 32 m standard single box double room simple supported beam bridge, when the box girder cross section action double line live load, the local torsion longitudinal stress of box girder with the increase of the high span ratio. Compared with the cross section, the warping ratio coefficient of the cross section is smaller than that of the cross section, and the warping ratio of the cross section is smaller than that of the corresponding control point. The local torsional longitudinal stress at the end of the roof flange of box girder is greatly influenced by the high span ratio, whether it is cross section or cross section. The warp ratio of the cross section is not more than 20%, and the warping ratio of the section is not more than 5%. It shows that the high span ratio of the current bridge good control of the local torsion stress of box girder under double line load, so the high span ratio of the current bridge is reasonable.