Monitoring of Tall Buildings to Assist the Design of Supplementary Damping Systems

Unlike visco-elastic and hydraulic damping systems, which are effective over a broad band of frequencies, TLDs, TLCDs and TMDs are tuned systems whose design requires accurate information on the periods of vibration of the building. The effectiveness of such devices is therefore much improved if they are tuned to the "as-constructed" periods of vibration which can differ appreciably from analytical estimates. Full-scale monitoring of a tall building towards the end and/or after the completion of construction provides valuable information on the "as-constructed" dynamic properties. Measured periods of vibration provide an important input to finalize the design of tuned supplementary damping systems. The effectiveness of such damping systems in reducing wind-induced building motions to acceptable levels also depends on good estimates of the inherent structural damping. Nominal values of the likely structural damping are used in the design of tall buildings. These can differ from the structural damping actually achieved for a constructed building. Consequently, measured values of the structural damping provide a valuable input for sharpening the estimated performance of the building under the action of wind. This paper summarizes monitoring procedures used at the BLWTL and provides examples of information obtained in such studies. Information from such monitoring is often for small amplitude motions and its applicability during stronger wind events requires interpretation. This requires interaction with the structural engineers. This early information on the `as-built' dynamic properties of a tall building is important for assuring effective operations of tuned supplementary damping systems.