Seismic Vibration Control of a Building by Overhead Water Tank Designed as Slender Tuned Sloshing Damper

Abstract

The possibility of detuning resulting from liquid depth fluctuation and low damping characteristics for being deep tanks hinder the utilization of overhead water tanks (OWTs) as tuned sloshing dampers (TSDs). This paper proposes a slender TSD (STSD) that can effectively serve as OWT as well. Unlike conventional TSDs, in an STSD, the liquid depth is allowed to fluctuate within any practically feasible range maintaining the condition h/D≥1, where h is the liquid depth and D is the tank dimension along excitation. For h/D≥1, the frequency and the lumped mass representative of the fundamental sloshing mode become independent of h. To improve damping, STSDs are provided with equally spaced horizontal ring baffles. It is shown that the effective damping ratio of the STSD with equally spaced horizontal ring baffles also becomes practically constant for h/D≥1. Thus, a consistent damper performance is possible despite liquid depth fluctuation. The mathematical model of the damper system is described followed by the design of OWT cum STSD for a real-life apartment building. Significant seismic vibration control of the building by the damper is demonstrated through a numerical study that shows consistent performance by the STSD despite 66.7% liquid depth fluctuation in the tank. The performance of the STSD is found to be comparable with conventional TSD.