Tension-bending coupled fatigue life study of semi-parallel steel wire cables using a developed LEFM method

Semi-parallel steel wire cables, specifically their anchorage segments, endure tension-bending coupled cyclic loads due to traffic and wind actions in existing cable-supported bridges. The fatigue life deterioration of spiral steel wires remains ambiguous in semi-parallel steel wire cables under such coupled cyclic loads because of its substantial diameter and helical configuration. To address this, the axial stress experienced by spiral steel wires located at cable anchorage segments was determined using a previously proposed analytical method for semi-parallel steel wire cables under coupled load in tension and bending. Subsequently, a corresponding fatigue life assessment methodology was developed, grounded in the principles of linear elastic fracture mechanics (LEFM). The developed methodology innovatively encompasses the crack propagation life within both the near-threshold and steady growth stages for steel wires inside bridge cables. The theoretical prediction of fatigue life for spiral steel wires inside bridge cables demonstrates strong agreement with relevant experimental results documented in the literature, with the relative difference being less than 11.1 %. Notably, the fatigue life of spiral steel wires inside bridge cables exhibits a nonlinear decrease with increasing cyclic load ranges both in tension and bending, respectively. The two cyclic loads emerge as the most detrimental load combination at a 0 phase difference situation for fatigue failure of bridge cables. Furthermore, the cyclic loads in tension and bending mutually suppress each other's effects for phase differences ranging from 0 to π/2. Apart from fluctuations in chord form, the fatigue life of spiral steel wires inside bridge cables generally increases along the longitudinal direction in a global trend. Remarkably, the fatigue life reaches its minimum values at the anchorage device end for spiral steel wires inside bridge cables, with the outermost steel wire exhibiting the shortest fatigue life. © 2024 Institution of Structural Engineers