Measuring and calculating the six change-in-length properties of fibre rope

This paper describes the methods for measuring and calculating the six change-in-length properties of fibre rope. These six properties completely represent how the length of fibre rope changes under various tension conditions and histories.

 The properties are: original stiffness, static stiffness, dynamic stiffness, construction strain, polymer strain, and working strain. These 6 properties are measured in a multi-step test program. The measured properties apply to the fibre rope material and construction. They are generally independent of rope strength and can be scaled to different rope sizes.

 The properties are not unique to a particular pattern of rope loading. Thus the tests need only be performed once for a particular rope design. They can be used to predict rope performance under any tension condition and history. Thus the tests need only be performed once for a particular rope design.

The test method was developed in the DNV industry-sponsored JIP “Improving Fibre Mooring Design Practices”. That research discovered or confirmed several important characteristics of fibre rope change-in-length properties. Those findings simplified the testing procedures and greatly reduced the number of necessary tests.

Author(s): Flory, J.F. & Ahjem, V.