Restrained Bending Fatigue Design of Bridge Cables

In previous work, certain shortcomings of traditional design approaches against restrained bending fatigue of axially preloaded spiral strands used in cable stayed structures (e.g. bridges) based on the extreme fibre direct stresses have been identified and subsequently resolved. Restrained bending fatigue life of such spiral strands clamped at the end(s), is shown to be governed by interlayer fretting fatigue. Interlayer fretting is found to be greatest near the so-called neutral axis and not the extreme fibre position, where, during tests, initial wire failures have invariably been found to occur. A new parameter has thus been developed for design against such rather common and often very costly fatigue failures. The reliability of any restrained bending design procedure is based on a reasonably accurate estimation of the minimum critical radii of curvature at the fixed end(s) with such values of curvature then used as an input into the fatigue design model. The present paper makes significant progress in resolving the longstanding debate in the literature as to whether the traditional method of assuming a constant effective bending stiffness for estimating such critical curvature(s) is a practically reasonable one.