Identification of Vortex-Induced Vibration on the Osman Gazi Suspension Bridge Tower and Mitigation by an Active Mass Damper

This paper describes a study on identifying vortex-induced vibration (VIV) of the Osman Gazi Bridge tower during construction and in-service conditions and its control strategy using an active mass damper. In the wind tunnel tests conducted before bridge construction, tower VIV was identified in the first out-of-plane tower bending mode despite the presence of aerodynamic corner cuts on the tower cross section. Bridge towers are made of steel boxes with inherently low damping, resulting in a VIV amplitude exceeding the limits for the workability and safety required in the design specification. An active mass damper (AMD) was proposed to mitigate tower VIV during construction and in-service conditions. The investigations of tower aerodynamic characteristics related to VIV in wind tunnel tests, design considerations, and implementation of AMD in construction and in-service conditions are presented. Unlike active control systems on other long-span bridge towers that were removed after construction completion, the AMD systems on the Osman Gazi Bridge tower continue to function even after bridge construction completion. This makes the AMD on the Osman Gazi Bridge the world's first application of a full active control system on a long-span bridge tower for in-service conditions. The AMD system was found effective in controlling the vibration under both conditions by providing additional damping higher than the requirement in the design specification. The robustness and effectiveness of the active control system are demonstrated in a 1-year full observation of AMD performance via a structural monitoring system. In general, the RMS of tower VIV accelerations under AMD control is lower than 15 cm/s2 or approximately 50% smaller than the corresponding accelerations without AMD control.