Frequency order and modal shifts in sagged cables

The free vibration of uniform isotropic cables has wide application in various engineering fields. In this study, the natural frequencies and modes shapes of vibration of sagged cables fixed at the same level are investigated using both numerical models and experimental results. The axial and torsional characteristics of the cable element are fully considered and a generalized cable finite element with six degrees of freedom model is formulated to describe the coupled dynamic motion of cable line in which longitudinal, vertical, and transverse translations and rotations included. The finite element model is applied to two cables that are replicated by experimental work. Results from the proposed finite element model are compared to the analytical solution of Irvine and Caughey [1]. Special focus is given to the influence of the non-dimensional parameter lambda 2, which defines the combination of geometric and material properties that influences frequency order. Excellent agreement found with experimental results that indicate significant levels of modal coupling that do not appear in analytical solutions.