A MATLAB Toolbox for Experimental and Operational Modal Analysis

Example: Steel transmitter mast

In the design process of a steel transmitter mast, the damping ratios of the lower modes are important factors. Dynamic wind load is the main loading condition of such a mast. To prevent malfunctioning of the antennae, the rotation at the top has to be limited. A vibration experiment was performed on a steel transmitter mast in order to determine these damping ratios. The mast is located in Antwerp, Belgium and is part of a cellular phone network. Since it is impossible to measure the true dynamic wind load acting on the structure, only response measurements were recorded and the mast constitutes an excellent real-life example to validate output-only system identification methods.

Pictures

Processing data

Time data (top) and power spectrum (bottom)

Identification results

Seventien modes were identified from the measurement data. Two of them are shown below.