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Tall buildings, due to their significant flexibility in horizontal direction, exhibit very limited inherent damping. As such, their resonance or near-resonance excitations induced by wind loads may result in lateral structural response values that exceed the serviceability limit states of the structure. A mass damper when attached on a tall building can significantly mitigate the near-resonance lateral response of the structure. Tuned liquid column dampers (TLCDs) which consist of one or more U-shaped vessels with partially-filled water are known as a common type of mass dampers. In the conventional type of these dampers, an orifice is located at the horizontal portion of the vessel to dissipate the energy of the oscillating liquid within the damper. In the new type of these dampers, the orifice is replaced by a coated steel ball that is immersed in water at the horizontal portion of the vessel to dissipate the oscillating energy of the liquid within the damper. The latter damper is termed as tuned liquid column ball damper (TLCBD). In this paper the performance of a set of different TLCDs and TLCBDs in response mitigation of a tall building (of 75-stories) under harmonic wind loads have been investigated. A large set of time history analysis runs have been performed to study the role of different damper design parameters on the lateral response of the tall building. The design parameters investigated in this paper include geometrical and mass properties of the liquid dampers, inherent damping of structure, and the frequency of input excitation. The outcome of analysis runs has been compared to highlight the cons and pros of TLCDs and TLCBDs in wind-response mitigation of the building. Results of this study indicate that both damper-types are effective in response mitigation of the original structure. The peak roof displacement is decreased by 50% to 88% as a result of using the liquid dampers in the structure. Given the mass and geometrical properties of dampers, the performance of TLCBDs will be superior to that of TLCDs in response mitigation of tall buildings. Based on the analyses conducted in this paper the attenuation of building deformations in a system equipped by a TLCBD is 5% to 25% larger than the case where the same system is equipped by a TLCD. However, the performance of TLCBDs is more sensitive to the frequency of input excitations. An increase in the mass of the damper, in both TLCD and TLCBD systems, results in an increased response mitigation. For instance, when the mass ratio of damper is increased from 1% to 5%, the peak lateral displacement of structure, depending on the type and geometry of damper, is further decreased by 30% to 50%. The length of the horizontal portion of the U-shaped vessel of the damper was found also to be significantly influencing the response mitigation efficiency of damper in both TLCD and TLCBD systems. When the length of the horizontal portion of the damper is increased from 0.5 to 0.9, the roof displacements experience approximately 30% to 40% further reduction.

Keywords: tall buildings, tuned liquid column dampers, tuned liquid ball dampers, vibration control, wind load

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