A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 2000

During design period, a 90-m-tall steel stack was found to have large across-wind response due to vortex resonance at low wind speed at which service life of the stack was sharply reduced. A pendulum Tuned Mass Damper (TMD) was chosen to be installed with the stack in order to provide additional damping, which is beneficial to control the response at resonance. It was designed to have a ring-shape mass in order to let it oscillates in any direction around the stack. Because the relative motion of the stack and the pendulum TMD was excessive at the optimal condition, the mass and the damping of the pendulum TMD had been increased to keep the relative motion within acceptable level without any losses in performance. To ensure that the pendulum TMD would be tuned with the stack, the parameters of the stack and the pendulum TMD were separately investigated. Geometric non-linearity of the cable and spring constant of the damper were also observed. The natural frequency, predicted by the finite element model, showed a good agreement with the measured value. It was observed that significant increases in damping level are produced by the pendulum TMD. The full-scale measurement of wind-induced responses of the stack and the pendulum TMD was set up four months after installation to monitor the performance of the pendulum TMD in service conditions. The responses of the stack had been recorded for almost two months together with wind speed and direction data. No significant reduction in the performance of the pendulum TMD in service conditions was found. The oscillation of the stack showed well defined along-wind and across-wind responses. Unfortunately, the vortex resonant response was not detected during the measurement due to very low wind speed.