An experimental study on the equivalent nonlinear model for a large-sized tuned liquid damper

A fire-suppression water tank is usually required at the top of a tall building. It would be economical to design a fire-suppression tank as a tuned liquid damper (TLD) during preliminary building design. A TLD has obvious advantages in terms of economy, maintenance, and damping efficiency with small vibrations. The sloshing nonlinearity of a TLD increases design difficulty. The purpose of this study is to investigate the nonlinear dynamic response of a large-scale TLD and provide an equivalent model for the TLD under small excitation suitable for the vibration comfort control of tall buildings. The nonlinear dynamic response was investigated through shaking table experimental results. An experiment was conducted with a TLD with a rectangular tank size of 2500 mm x 1750 mm and a sloshing period of 3.2-6.2 s. A series of TLD tests were performed with different flow-damping devices, water depths, and excitations. The time history of the water sloshing wave height was obtained using a video recognition method; the base shear force of the tank was measured simultaneously. A new nonlinear stiffness and damping model (NSD-h) was proposed that simplified the TLD as a nonlinear tuned mass damper (TMD) to predict the tank base force. In the NSD-h model, the equivalent wave height was introduced to describe the sloshing amplitude of the TLD. The nonlinear frequency and damping ratio of the TLD were calculated using the equivalent wave height. Verified in wind conditions, the NSD-h model demonstrated significantly higher accuracy than the nonlinear stiffness and damping model (NSD) with similar simple equations.