Monitoring of the Dynamic Behaviour of a Telecommunication Tower

The dynamic behaviour of an almost 200 m tall telecommunication tower has been monitored for about eight years. It consists of three structural sections: a reinforced concrete shaft that carries a tubular steel section and a hollow glass fibre reinforced plastic cylinder at the top. Beside the structural response at different levels, also the temperatures at different locations of the steel section as well as wind speeds and directions have been measured. Based on the acquired data, the modal parameters of the structure have been continuously identified by means of an automated procedure. From the identified results, several conclusions concerning relations between environmental conditions and the dynamic behaviour of the system could be drawn.

These relations do not only concern seasonal changes of the natural frequencies due to varying temperatures. Also system changes, such as icing of the structure, can be identified from modal parameters. Additionally, very interesting non-linear dependencies of natural frequencies and modal damping ratios on the vibration amplitudes have been observed. It is very likely, that these system nonlinearities are caused by the bahaviour of the tuned mass damper installed at the tower’s top. Further analyses are carried out for the sake of an enhanced interpretation of the findings from the monitoring data.