Modal response of a tapered lightning tower subjected to vortex-induced vibrations

This study experimentally investigates vortex-induced vibrations (VIV) on a cylinder and a tapered cylinder model of a lightning rod mast with high slenderness. The cylindrical model exhibits a narrow, well-defined VIV peak, while the tapered cylinder displays multiple broad peaks due to the variation of diameter along the body, leading to an extended lock-in range. The lower-order modes contribute marginally to the response, while higher-order modes dominate the dynamics. Ramp up and ramp down tests showed no hysteresis behaviour for both structures. These findings highlight potential limitations of Eurocode approaches that focus mainly on the first mode. Future work will include experimental testing of intermediate geometries of the mast and enhanced instrumentation to provide detailed measurements and further validate the observed trends.