Research on Torsional Characteristic and Stiffness Reinforcement of Main Girder of Half-Through Truss Bridge

Abstract

The stronger stability of a half-through truss bridge can improve the bridge performance for resisting extreme loads, such as earthquakes and shock. To improve the bridge stability, it is necessary to improve the torsional stiffness of the half-through truss bridge. To study the torsional characteristics of the main girder of the half-through truss bridge, the half-through truss is equivalent to an open slot thin-walled member, and the calculation formula of the free torsional moment of inertia of the main girder is deduced. Because the main truss can resist warping deformation through bending, it has a great contribution to the torsional stiffness. Based on the vertical bending action of the main truss, the calculation formula of the correction of the torsional moment of inertia of the main girder is deduced. Taking a half-through truss pedestrian bridge as an example, the torsional moment of inertia of the bridge under different width-span ratios is calculated by theoretical and finite element analysis. The results show that when calculating the torsional moment of inertia of the main girder of the half-through truss bridge, the free torsional moment of inertia calculated by the equivalent open slot section is very different from the actual torsional stiffness, and the bending correction value must be considered. The theoretical solution after taking into account the corrected value is well-fitted with the finite element results. The theoretical formula can be used to explain the torsional mechanism of this kind of bridge. According to the mechanism research, the method of installing X-shaped longitudinal supports between the upper transverse girders to improve the torsional stiffness is finally formulated. Installing the X-shaped longitudinal supports not only can keep the size of the half-through truss bridge unchanged but can also have a considerable enhancement effect, which will significantly improve the torsional stiffness and stability of existing bridges.