Calculation Method for Torsional Angle of Main Cables of Suspension Bridges with Spatial Cables

In suspension bridges employing spatial cables, the main cables undergo torsion during the construction process. Clarifying the distribution pattern of the main cable torsional angle can guide the positioning and installation of cable clamps and mitigate issues such as wire waving. This paper provides a theoretical calculation method for the distribution law of the torsion angle of the main cable. Firstly, it is assumed that the load form that causes the torsion of the main cable is the uniform load along the cable length and the span length. The theoretical calculation formulas of the torsion angle are derived, respectively, and the two formulas are compared. Analysis shows that under a uniformly distributed load, when the main cable is deflected at a certain angle, the torque is non-uniformly distributed along the cable, and the torsional angle follows a fourth-order parabolic curve along the span. A model test on spatial cable deflection was conducted, and the measured torsional angles were compared with theoretical results. The findings indicate that the measured torsional angle variation along the span is generally consistent with theoretical calculations. When the deflection angle of the spatial cable is large, the theoretical value exceeds the measured value. Furthermore, a finite element model was employed to calculate the torsional angle, torque, and bending moment during cable deflection. The results reveal that the distribution of the torsional angle depends on the ratio of the moment of inertia and the polar moment of inertia of the main cable section. The smaller the polar moment of inertia relative to the moment of inertia, the closer the torsional angle is to the spatial deflection angle. When the polar moment of inertia is relatively small, except in the end regions, the distribution of torque obtained from simulations is largely consistent with the theoretical values.