FREE BENDING CHARACTERISTICS OF AXIALLY PRELOADED SPIRAL STRANDS

Spiral strand plane-section bending behaviour in connection with large radii of curvature is analysed initially, and theoretical results are presented for bending stiffness and overall hysteresis which are amplitude dependent. Owing to interwire friction, plane-section bending stiffness is found not to be constant. The theory is capable of estimating the upper (no-slip) and lower (full-slip) bounds to plane-section bending stiffness, and the transition between the two limits as a function of the imposed radii of curvature. For small radii of curvature, interlayer slippage can occur on the trellis points of contact, and plane-sections do not remain plane during the bending cycle. Using a corrected and subsequently extended version of a previously reported theoretical model, an insight is given into the mechanism of interlayer slippage with associated substantial reductions in the effective bending stiffness. This has been achieved by developing two rather different methods which provide a theoretical double check, and both of which take geometrical non-linearities and effects of line-contact (hoop) interwire forces (previously ignored in available literature) fully into account. The present model should prove useful in connection with aerodynamic or hydrodynamic analysis of axially preloaded spiral strands in, for example, offshore platform, bridging and guyed mast applications.