Modified Deflection Theory for Preliminary Design of Self-Anchored Suspension Bridges

A modified deflection theory is developed for preliminary design of self-anchored suspension bridges. The proposed theory modifies the questionable approach of the existing theory considering the initial fabrication camber and overcomes the limitation that the hangers are assumed inextensible, which results in a stiffer bridge system and thus underestimation of the main cable and girder deflections. In addition, in order to avoid the inconvenience of solving a system of nonlinear equations iteratively for the preliminary design, the tower flexural stiffness is neglected rationally to obtain a system of linear equations only. With the aid of all force equilibrium and deformation compatibility conditions for the entire bridge system, the modified deflection theory is formulated. Its solution procedure is presented, which leads to a complicated sixth-order variable-coefficient ordinary differential equation, and a practical approximate solution to the equation is sought. To verify the proposed theory, a bridge example is investigated, and the results are compared to those from the previous deflection theory and complex finite element analysis. The comparisons demonstrate the effectiveness of the modified deflection theory.