Telecommunication structures are designated as post-critical facilities that must remain operational after a design-level earthquake has struck. Since it is difficult to obtain experimental results on the response of these structures when subjected to measured wind and earthquake loads, numerical simulations based on detailed finite element models are the most common way to predict their dynamic response. Many such studies have been published, which in spite of having been conducted with care and expert knowledge, have not been validated with experiments. The degree of uncertainty in modeling complex structures is difficult to assess, even in controlled laboratory conditions. Tall guyed masts exhibit nonlinear geometric response that is difficult to replicate in reduced laboratory models, and full-scale investigations are preferred. This study reports ambient vibration test results obtained on a 111.2 m guyed telecommunication tower owned by Hydro Quebec and located in St. Hyacinthe, Quebec. Acceleration measurements in the guy wires allowed determining the cable tensions while ambient velocity data collected for the mast allowed extracting the dominant natural frequencies and mode shapes (and corresponding damping estimates) for the guyed mast. These experimental results were compared with those obtained from the numerical eigenvalue analysis of detailed finite element models of the tower with various adjustments in cable tensions in the numerical model. The results confirmed that cable tensions are a very influential parameter on the global mast frequencies and the study underlined the importance of considering a range of realistic tension values in numerical models to obtain bounded values of natural frequencies and dynamic response.
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