Nonlinear dynamic interaction between cables and mast of guyed-tower systems subjected to wind-induced forces

Guyed towers are special structures widely used in communication industry as antenna-supporting structures. A guyed tower is a nonlinear structural system in which the mast, consisting of single beam-column or multiple members (trusses) is supported elastically at various points along its height by inclined pretensioned cables with their ends anchored to the ground. As a result of the overall slenderness and flexibility of the system, guyed tower exhibit a high degree of nonlinearity and dynamic sensitivity to turbulent wind excitation. Thus to obtain reliable structural responses of the vibrating tower, a 3-D nonlinear dynamic analysis is mandatory.

This research work comprehensively investigates the important subject of dynamic interaction between the mast of a guyed tower and its supporting cables when the tower is excited by turbulent winds. To achieve this objective, a comprehensive set of analytical studies are pursued and relevant mathematical models are obtained. In the following a brief description of each of these studies is given.

The first study involves a new and general nondimensional finite difference formulation that considers all the important parameters influencing the vibration characteristics of guy cables. The second study complements the first one by investigating the stability and convergence of the Newmark-p; step-by-step integration technique and their dependence on both spatial and temporal discretization parameters.

The third study proposes new dynamic and quasi-static computational procedures to model the wind-induced forces on cables and bars. The procedures utilize generation techniques for wind speed records and take into consideration the major characteristics of both the exciting wind and the vibrating cable. It also implements experimentally obtained data for the drag and lift force coefficients for different wind angle of attack.

The final study provides a comprehensive description of a new methodology for the nonlinear dynamic analysis of guyed towers. This methodology implements the mathematical models and computational procedures obtained from the above-mentioned studies to perform a time domain analysis. This analysis provides a complete description of structural behavior of the guyed tower in terms of its nodal responses and mast member forces, in addition to guy cable tensions. The study also provides useful comparisons between different analyses using static and dynamic models for the guying cables as well as comparisons between static and dynamic analyses of the whole guyed tower.

The research outcomes are of great value for both researchers and engineers involved in the nonlinear dynamic analysis and design of guyed towers. Moreover, the analytical models and methodologies involved in this research can be extended to other cable-supported structures applications.