Antislip Safety of Double-Cable Multispan Suspension Bridges with Innovative Saddles

Compared with suspension bridges with a single main cable in each cable plane, adding a cable with a different sag may increase the vertical stiffness, but also increase the demand of frictional resistance at the saddles. To ensure antislip safety, the frictional resistance must be greater than the unbalanced cable tension. This study presents an innovative saddle to accommodate two main cables and analyzes the frictional resistance through mechanical analyses that were validated by finite-element analysis. A nonlinear finite-element model of a double-cable three-tower suspension bridge is established to determine the maximum unbalanced cable tension. The effects of key design parameters on antislip safety are investigated. The results reveal that the proposed saddle structure increases the frictional resistance. Strategies to enhance antislip safety include increasing the flexural stiffness of the middle tower, the ratio of dead load distribution, and the sag of the top cable. Decreasing the sag of the bottom cable helps improve the antislip safety of the top cable but compromises the safety of the bottom cable. This study provides new insights into the design and evaluation of multispan suspension bridges.