Methods Study Of Applying Prestress In Steel-concrete Composite Continuous Beam Bridge

Currently, the steel-concrete composite beam bridge is an important branch of the bridge constructions. This kind of bridge can connect the upper concrete deck slab with the lower beam through the shear connector, which will make full use of the tensile strength of steel and the compressive strength of concrete. Those multi-span composite beam bridges, the span more than 25 m, always employ the continuous beam structure. However, the pivot of the steel-concrete composite beam bridge is in the negative moment region, which will make the upper concrete deck slab under tension, the lower steel beam under pressure. This kind of forcing conditions are not advantageous. Therefore, some measures would be taken to improve this situation in the negative moment region of steel-concrete composite beam.This paper briefly introduces some common ways of implementing prestress in the steel-concrete composite beam bridges and elaborates on the calculation theories. This paper takes a three-span steel-concrete composite beam bridge as example, the Xiaoxihu overpass bridge in Lanzhou. The whole construction process is calculated through the Midas Civil software which establishes the finite element model. The prestress of steel box beam, the prestress of bridge deck slab, and the deflection will be obtained through analysis of the calculation results, which will show the change rule of the stress and the displacement of every construction stage.This paper changes the parameter of the example finite element model and then analyze it in order to study the influences of the different ways for applying prestress on the performance of composite beam bridge. This study changes the parameters of jacking force, the location of the jacking force, the tensile force of the prestressed steel bars, the whole casting at time of the bridge deck slab or not, the filling concrete or not in the steel box bottom deck of the pivot negative moment region. Compared with the structure prestress, the calculation result of the stress and the displacement, there are some conclusions that can be obtained. These conclusions are as follows: 1. The jacking force of the span has relatively big influence on the stress and the displacement, and the force condition in jacking point is not favorable. 2. The prestressed steel bars will increase the deck stress, which will improve the force condition of the concrete deck slab. 3. Casting by stages of the bridge deck slab will decrease the pulling stress, but the division of the casting should connect with the arrangement of the steel bars. 4. Filling in concrete in the bottom slab and the pier top of pivot negative moment region, which will obviously decrease the stress of steel box beam.