Abstract: Steel structure bridges are constructed in large sections and are prefabricated in factories. The precise setting out of the line shape of the plates is the most important for the precise control of the line shape of the steel structure manufacturing. The flying geese shaped steel structure arch rib curve is complex, and the height of the arch rib section changes linearly with the arch axis, which brings great difficulties to the manufacture and processing of the steel structure. The theoretical solution of the design of the bridge arch ribs to the bridge line and the pre-curvature line can provide the theoretical support for the subsequent processing and manufacturing of the steel structure arch rib top and floor, and the precise layout of the plates, and provide the guarantee for the stability of the steel structure arch rib after the bridge completed. The theoretical manufacturing line shape of prefabricated steel box arch ribs is an important technical indicator to ensure the smooth installation of the parabolic parabolic deformed section steel box arch bridge and the reasonable stress on the bridge during the service period.
Through the software MIDAS, the bridge theoretical calculation model was established, and the influence of construction process transformation on the arch rib bridge line shape, such as tensioning the prestressed tie bar, removing the arch rib mounting bracket, tensioning the suspender, removing the main beam under the bridge support, secondary tensioning suspender and so on, was analyzed. And the theoretical camber value of steel arch rib system transformation during construction and erection was obtained. Combined with the calculation equation of the arch axis of the special-shaped steel box arch rib given in the design drawings, the coordinate system of any point O point on the arch axis and the coordinate system B of the adjacent point B on the arch axis that was infinitely close to O point through the coordinate conversion method 2, and the original coordinate system of the whole bridge established the connection between the three. The triangle similarity relationship between the three was determined through the relationship between the position coordinate of point O in the original coordinate system, the position coordinate of point B, and the cross-sectional height H at point O in combination with coordinate system 1 and coordinate system 2. In order to obtain the geometric relationship between the top, bottom, diaphragm and hanger manufactured by the special-shaped steel box arch rib under the bridge state and the arch axis calculation equation, the independent bridge line shape of the steel box arch rib top and bottom plate determined the calculation equation.
The curve of the arch rib formed by this calculation formula was in good agreement with the design line given by the design institute. When x₂-x₁=0.5 m, the maximum deviation is 2 mm, which proved the correctness of this method. Then, through the calculation equations under the bridge completion state, combined with the pre-camber value of each point of the arch rib curve calculated by the MIDAS model, the calculation equations of the roof, bottom plate, diaphragm, and hanger of the steel structure arch rib without stress were solved. The curve state determined by this calculation equation was the line shape of the rigid arch rib without stress. Using this calculation result, the curve of the unstressed state was 80 mm longer than the design line of the completed bridge. This calculation method effectively solved the problem of precise setting out in the unstressed linear manufacturing process of the prefabricated factory of special-shaped steel box arch ribs.