Live load response assessment for double-cable triple-tower suspension bridges: A continuum model-based analytical method and case study

Double-cable suspension bridge is a novel concept to addressing the middle tower effect in multi-tower suspension bridges, offering broad application prospects. This study develops an analytical continuum model for the double-cable triple-tower suspension bridge (DTSB) based on the deflection theory. The model incorporates the effects of hanger expansion, the flexural stiffness of the stiffening beam, and the lateral stiffness of the tower. Differential equations for the coupled vertical displacements of the main cable and stiffening beam are derived from stress analysis under dead and live loads, with horizontal cable force increments eliminated using the longitudinal compatibility equation. The equations are then simplified using the Galerkin method. A case study with a DTSB layout of 860 m+ 1070 m is conducted, and the analytical results are validated against the finite element method, demonstrating the method's accuracy. A parametric analysis explores the effects of structural layout and structural stiffness on the maximum deflection of the stiffening beam and lateral displacement of the middle tower. It is found that the sag-to-span ratio of the lower cable significantly affects the structural response, while the dead load distribution in the upper and lower cables has little impact. Unequal span lengths aggravate the stiffening beam’s maximum deflection and the middle tower’s lateral displacement, while higher axial stiffness of the main cable, hanger, and tower reduce them. Neglecting hanger expansion results in an underestimation of the calculation results.