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

Wound cables and straight rods exhibit lateral instabilities when loaded un der compression and rotation in fixed-grip conditions. In a multi-strand ca ble made from helically wound strands, this produces a "bird cage" structur e where the constituent strands separate to leave a central void region. Fo r a straight rod, a similar instability occurs when the planar elastica bec omes unstable under significant axial compression. The large deflection the ory of linear elastic rods is used to explain these behaviours in terms of the standard concepts of the theory of buckling, post-buckling, and imperfe ction sensitivity. The problem provides an excellent vehicle for the use of Euler parameters (quaternions) which remove the singularities normally ass ociated with an Euler angle formulation. (C) 2001 Elsevier Science Ltd. All rights reserved.