Dynamic excitation of cables by deck and/or tower motion

Large-amplitude cable vibrations have been observed on many major cable-stayed bridges. One possible source of excitation is movement of the deck and/or tower. Of particular concern is parametric excitation, whereby small deck/tower motion at one frequency can cause large cable motion at half the frequency under certain conditions. More commonly, deck/tower motion causes direct excitation of the cable at the same frequency in the same plane. Since cables have low damping, the response amplitudes can be large and geometric non-linearities can become important. Current design guidelines treat the axial and transverse components of end motion separately, but for an inclined cable subject to vertical deck motion at the lower anchorage and/or in-plane horizontal motion at the upper anchorage, both components occur simultaneously, modifying the behaviour considerably. This paper gives simplified results of non-linear mathematical modelling of inclined cable dynamics, with experimental validation, with the aim of providing more reliable guidelines for use in design. The proposed guidelines are summarised an appendix.