BUFFETING RESPONSE OF TOP-MOUNTED ANTENNAS ON GUYED MASTS

摘要

Top-mounted antennas cantilevered above guyed masts are vulnerable to increased levels of dynamic response due to turbulent buffeting from wind. In addition to the effects of gusts acting on the antenna itself, wind-induced vibration of the flexible mast below can further excite the antenna, producing a whip-like action capable of generating large dynamic bending stresses at the base the antenna. While the dynamic sensitivity of cantilevered antennas is not explicitly recognized in most guyed mast design standards, it has been linked to at least one major guyed mast collapse. In the current study, the dynamic response of guyed masts with top-mounted antennas is investigated numerically using frequency domain analytical methods for a range of mast and antenna configurations. The results indicate that the mast-antenna system is highly coupled, with dynamic behavior depending on a number of factors including the relative stiffness, mass and span lengths of the mast and antenna, as well as on the overall structural characterisitcs of the guyed mast assembly. Furthermore, cantilevered antennas deemed to be slender relative to the mast below were found to exhibit significantly higher levels of dynamic response than those typical for the mast as a whole. In large part, the increased dynamic response could be attributed to elevated resonant participation of vibration modes dominated by flexural motion of the antenna.