Nonlinear dynamic response of a three-dimensional guyed mast

Abstract

Guyed masts are examples of structures extensively used in Civil Engineering. During the service life of the structure, the guys tension values can vary due to various circumstances. The consequences can range from operational difficulties to failure of the structure or some of its components. Thus, a study of the sensitivity of the dynamic response of a guyed mast to the initial pretension of the guys becomes relevant. A three-dimensional guyed mast is herein represented by a beam-column and one level of three nonlinear inclined cables, with a prescribed dynamic lateral load acting on the mast. The second order effect of the axial load due the cables pretension on the mast is also considered. The load is designed to avoid resonance effects and meet the maximum displacements limits within the Euler-Bernoulli theory used in the beam-column model. The guys behavior is represented with cable nonlinear equations that account for the extensibility and the initial deformed state due to gravity. The governing system is discretized using finite elements and solved in the time domain through Newmark and Newton-Raphson algorithms. An ad hoc algorithm was developed by the authors as a tool to analyze 3D guyed masts with an arbitrary number of guys and levels of guys. A natural vibrations study shows that a single eigenvalue could be associated to local cable or mast modes or global cable-mast modes, depending on the initial pretension. The displacements of the mast at two strategic points exhibit a rich range of dynamic responses, which can turn from periodic to nonperiodic motions (among other bifurcations) within small ranges of variation of the initial pretension.