Study Of Large Curvature Continuous Structural Performance For Steel Bridge

The curved steel box girder has many advantages such as succinct and beautiful appearance, light structure weight, best stress performance, good torsion rigidity performance, manufacture process simply and construct in a short time, well meet the demand of the terrain limitation, also, the general cost is not very high and etc.. Therefore, it is widely used in city viaducts and crossroads. Especially in cross lines, cross ground crack such special occasions with brilliant development prospect. Then, there are important realistic meanings in the study on this kind of bridge.In this paper, it has fully research on the ultimate load carrying capacity and the shear-lag effect of the continuous steel box girder with large curvature. First, there is a discussion about the concept of the structure load carrying capacity, type, stability, analysis principle, calculating method and the method to solve the ultimate load carrying capacity, the basic concept of shear-lag effect, etc.. Second, by using the finite element to analyzing the structure ultimate carrying capacity through the whole process. Including analysis of load carrying capacity under the allowable stress control, steady bucking eigenvalue, nonlinear stated ultimate load carrying capacity. Divide the stiffener area to the box girder cover plate equally, and then simplify the steel box girder to the ordinary box girder. Adopt calculus of variations to solve the problem and compare with space finite element. Thus, put forward the approximate calculation of shear-lag coefficient for the non-cantilever plate steel box girder. Next, according to space size, material characteristic, connection way of the original bridge, make the 1/10 of the proportions model bridge. By analyzing the result of experiment and theory calculation to research the rules of the mode of failure, the ultimate load carrying capacity, and the spear-lag effect. At last, according to the experiment and theory results to draw some related conclusions. The most unfavorable section of the carved steel box girder is 5000mm span middle section. There are 2-5mm cracks in width appeared in bottom board weld of the middle section, the outside web weld and the inside web weld in that section when the model bridge is destroyed. Under the concentrated load condition, the minimum load carrying capacity of Model Bridge is 63kN; under the uniform distributed load condition, the minimum load carrying capacity is 45kN/m2; although, the maximum stress of the model bridge which correspond in actual bridge design load test is 29.61MPa. It can be known from elastic range that structure load carrying is over than design load. Considering the factors such as material nonlinear and geometry nonlinear that under the concentrated load condition, the actual ultimate load carrying capacity of structure is 156.7kN, under the uniform distributed load condition, the actual ultimate load carrying capacity is 111kN/m2.The design load of actual bridge correspond in model bridge test load is 11.41kN. In the other word, the safety coefficient of the model bridge is up to 13.7. The structure of the model bridge may lose stability partly in stability analysis. Usually in web and cross board. With highly safety factor, it will not appear lose stability phenomenon. Because of the structure feature of non-cantilever plate steel box girder, the changing range of steel box girder section's vertical normal stress along with cross section is not very obvious. And the changing rule is more complicated; Due to the compressive region error between theory value and test value, the suggestion is adoptβ-λ, as the compressive region to enhance the stress coefficient. Also this text includes the study of shear-lag effect of the model bridge in elasticity, elasticity and plasticity, complete plasticity.Under the complete plasticity state, the span middle section has the best performance of shear-lag effect, and therefore, the bottom board has not obvious performance through the whole process; On the other hand, the pivot top section board has best performance of shear-lag effect under the elasticity state, the bottom board does a good job on the complete plasticity state either. No matter under the action of concentrated load or uniform distributed load, as the same section, plus or minus shear-lag effect can appear at the same time. Every joint along the bridge vertical direction, plus or minus shear-lag effect may appear at the same time. Under the action of concentrated load or uniform distributed load, there are not much differences between single,double compartments models and three,four compartments model of shear-lag effect actually. The shear-lag effect of three,four compartments model is much low; As the opposite stress of the third compartments model is much strong, thus, we need to enhance structure design at the rack. For the single box forth compartments section model, the two definitions of the curved girder shear-lag effect coefficient-λ1,λ2 are nearly same, but bothλ1,λ2 will not become the same with the number of compartments had been added.This text can offer references in calculating of design for the continuous steel box girder with large curvature and offer the technical data for criterion revision of steel bridge.