Load Transfer and Recovery Length in Parallel Wires of Suspension Bridge Cables

A new simplified contact model aimed at capturing the load transfer and recovery length in parallel steel wires, commonly used in main cables of suspension bridges, is presented. The approach is based on placing elastic–perfectly plastic spring elements at the contact region between the objects. These springs have varying stiffness (Model I) or yielding (Model II) depending on their proximity to the clamping loads. Their stiffness or yielding is highest when they are closer to this force, and it decays when they are farther away from the clamp. This decayed behavior is assigned according to Boussinesq’s well-known solution to a point load (applied on a half space). Both models converge quickly compared with a full contact model and recover Coulomb friction law on a two-dimensional (2D) benchmark problem. Moreover, when the same properties are chosen for all springs (disregarding Boussinesq solutions), the models reduce to the classical shear-lag model, which for high clamping (point) loads gives inaccurate results. The spring models are validated experimentally on a seven-wire tightened strand. In this case study, the outer wires are axially pulled, whereas the middle wire, slightly shorter than the outer wires, experiences no direct applied axial load. However, because the strand is radially fastened at several locations, the axial load is transferred to the inner wire by an interfriction mechanism between the wires. The strains at the center points of the outer and inner wires are measured via neutron diffraction for different clamping loads, showing that the inner wire is capable of recovering most of the load.