Calculation Method for Deformation of Three-Tower Cable-Stayed Bridges

The structural deformation induced by live loads represents a significant consideration in the design of three-tower cable-stayed bridges. The study proposes a deformation calculation method for three-tower cable-stayed bridges, which can be used to assess whether the structural stiffness meets requirements during the preliminary design stage. Based on the elastic foundation beam theory, analytical expressions for the longitudinal constraint stiffness of the cables and the main girder on the middle tower are derived. Furthermore, analytical formulas for the longitudinal displacement at the top of the middle tower and the midspan deflection of the loaded span under live load are established. Finite element analysis demonstrates strong concordance between the theoretical values and the results obtained from the model. In addition, the influence of cable and girder design parameters on their longitudinal constraint effects is analyzed based on the proposed analytical expressions. The study indicates that once the cable stress level reaches 600 MPa, further increases in stress yield diminishing returns in enhancing constraint stiffness; increasing the cable cross-sectional area is more effective in improving longitudinal constraint stiffness than enlarging the main girder’s moment of inertia.