Birdcaging and the collapse of rods and cables in fixed-grip compression

D.M. Stump & G.H.M. van der Heijden

Wound cables and straight rods exhibit lateral instabilities when loaded under compression and rotation in fixed-grip conditions. In a multi-strand cable made from helically wound strands, this produces a `birdcage' structure where the constituent strands separate to leave a central void region. For a straight rod, a similar instability occurs when the planar elastica becomes unstable under significant axial compression. The large deflection theory of linear elastic rods is used to explain these behaviours in terms of the standard concepts of the theory of buckling, post-buckling, and imperfection sensitivity. The problem provides an excellent vehicle for the use of Euler parameters (quaternions) which remove the singularities normally associated with an Euler angle formulation.

keywords: birdcaging, wound cable, lateral instability, post-buckling behaviour, imperfection sensitivity, Euler parameters, perturbation analysis

Int. J. Solids Struct. 38, 4265-4278 (2001)