Simple determination of the maximum axial and torsional energy dissipation in large diameter spiral strands

By using an extensive series of theoretical parametric studies, covering a wide range of realistic spiral strand constructions, simplified (hand-based) procedures are developed for obtaining the maximum values of axial and/or torsional frictional specific loss (hereafter referred to as axial and/or torsional specific loss) in fully bedded-in and axially pre-loaded multi-layered spiral strands subjected to steady cyclic loading. The theoretical parametric studies, which are based on a previously reported orthotropic sheet model, have also led to the development of equally simple procedures for estimating the values of critical (axial load range/mean axial load) and range of twist at which maximum axial and torsional specific loss occur. It is shown that, over a wide range of strand mean axial strains, the axial specific loss may be significantly increased by quite modest increases in the lay angle (within the current manufacturing limits). For a given strand construction, increasing the lay angle is, however, shown to lead to a reduction in the magnitude of maximum torsional specific loss. Guided by the previously reported experimental observations, the possible practical limitations of the proposed formulations are critically discussed. The present work should prove of value to those involved with the design against aero- or hydrodynamic instability of cable supported bridges and offshore platforms, as well as overhead transmission lines.