The effect of specimen length on testing of parallel-element ropes

Parallel-element ropes are used as mooring lines on floating platforms in deep water. Individual yarns, strands, or subropes are arranged as parallel components. This produces a very efficient and compact rope structure. There is much interest in testing these ropes for strength, extension, and damage-tolerance properties. By necessity, the rope test specimen is much shorter than the rope mooring line, but rope length can affect important rope properties. Unbalanced element lengths cause a large force imbalance in a short specimen but this effect is minimal in much longer ropes. Damage to a portion of an element may greatly reduce the force in that element in a short rope but may have little effect on that force in much longer ropes. This paper analyzes potential length-related effects and presents equations and graphs comparing the effects. The paper will interest planners of rope test programs and designers who must use short-rope test results to design long-rope systems.