Damping Behaviour of Slender Telecommunications Structures

During the last two decades, the development of mobile telecommunications (‘telecoms’) technologies has resulted in an increased number of antennas to be accommodated around us on different kinds of structures. From new, short monopoles to old high guyed masts, all are considered sensitive flexible structures under wind, many of which are required to hold more equipment than their initial design loading capacity. The dynamic analysis of these structures has been neglected for years, in part as it is clearly a field that requires further investigations with new modern methodologies and knowledge. Within the industry, damping is the topic that provides the most uncertainty between existing expert consultants. The complex nature of damping arises from the high deviation between similar structures and the number of involved sources that modify this behaviour, from boundary conditions to aerodynamic effect, or nonlinear amplitude and frequency dependence relationship. In this PhD research, several projects related to response-data acquisition were used to determine how damping behaves for each selected typology structure (monopoles, lattice towers and high guyed masts). Old and new estimation techniques have been applied after human and wind-ambient excitation to provide reliable data to verify current approaches of assessing damping and provide new clues and perspective about understanding damping in this kind of structures. The research counts on a study of the generic structural damping component on short structures compounded by soil-foundation component and material-connection defined by free decaying responses. A study of non-linearities exist on the response that help to determine sources of damping, and finally, diverse studies of monitoring systems under wind excitation were carried out to allow the research to study actual service response to extract aerodynamic damping, and the accuracy of current drag factors for different wind effects. This new perspective provides essential knowledge to structural engineers when designing current and future structures, advising on the effectiveness and feasibility of external damping providers, not just as an option to minimise aeroelastic vortex shedding effects, but also to reduce the buffeting response with the consequential structural capacity improvement. Results also show the deficiency of current standards and recommendations in the estimation of dynamic properties, especially on damping matter