The Analysis of Masts and Towers

Abstract

For many years both guyed masts and self-supporting towers have been used for supporting antennas for mobile and other communications. The choice between masts and towers has often been determined by the tradition. However masts have its clear advantages in the open country, whereas the towers are more likely to be chosen in the urban areas.

Masts and towers are often used for broadcasting of radio and television or antennas for cellular phones. The masts and towers consequently are situated on the top of hills and mountains, where the climate often is extreme with respect to wind load and in some cases due to atmospheric icing. Since the wind is turbulent and the masts and towers are flexible and sensitive to dynamic load, the dynamic response becomes important in the analysis of towers and guyed masts. However there are some differences in the analysis of masts and towers.

The wind resistance for lattice sections is dependent on the type of members, the solidity of the sections and for tubular members also dependant on the Reynolds number. Furthermore, latest research within the IASS Working Group for Masts and Towers has shown that the wind resistance of tubular sections is dependent on the turbulence of the wind.

The masts act strongly in non-linear fashion since the guy ropes are varying from slackened to a taut string. Over the years different methods have been used for analysing guyed masts making the methods more and more realistic: starting by a gust factor method, over the IASS patch wind method to the Eurocode patch wind method, which gives results close to the results from a stochastic analysis and the time domain analysis.

The towers do not act as non-linear as the masts. However, the towers are also sensitive to the dynamics of the wind and a dynamic factor should be applied depending on the turbulence of the wind, the height of the structure etc.