BIRD-CAGING IN WIRE ROPE

Wire rope is a structural element that is generally used to resist relatively large axial loads in comparison to bending and torsional loads. In many cases, rope is subjected to impact loads that send axial and torsional responses up and down the rope. A theory is presented that predicts the contact force between an outer strand and a core strand in a rope (or an outer wire and a core wire in a strand) subjected to an axial impact load. When the contact force remains positive, no separation occurs. If, however, the contact force becomes negative somewhere along the rope, the outer strands will separate from the core strand. When this separation strains the rope material beyond its elastic limit, instability or bird-caging occurs in the form of a permanent deformation. This theory predicts an interesting situation in which bird-caging can occur even when the rope remains under a positive axial strain. Hence, the rope does not have to go into compression for bird-caging to occur. © ASCE.