Adaptation of a Deep Liquid-Containing Tank into an Effective Structural Vibration Control Device by a Submerged Cylindrical Pendulum Appendage

Abstract

Due to a high proportion of impulsive liquid mass and low inherent damping, liquid-containing deep tanks, such as conventional overhead water tanks, are generally not considered for design as tuned liquid dampers (TLDs) for passive vibration control of structures under lateral excitation. This paper presents a novel concept to convert deep tanks into effective vibration control systems through the incorporation of a submerged cylindrical pendulum appendage (CPA). The CPA is placed in the impulsive liquid zone of the tank and its oscillating frequency is tuned to the dominant frequency of the primary structure. When laterally excited, the primary structure transfers vibrational energy to the CPA, thereby setting it into oscillation. The motion of the CPA is opposed by the drag exerted by the surrounding liquid on it, which leads to dissipation of the vibrational energy. This particular design utilizes impulsive liquid mass in the energy dissipation mechanism, while allowing fluctuation in the liquid level in the upper region of the tank, thereby fulfilling the functional requirements of the tank. In this paper, the mathematical model and working principle of the deep tank with CPA (DT-CPA) damper are developed. The equations of motion of a two degree-of-freedom (2-DOF) structure-damper system are derived. The design of the DT-CPA damper is illustrated considering an example structure and the performance of the damper is examined by subjecting the structure-damper system to pre-recorded seismic base excitations. The sensitivity of the performance of the proposed damper to tuning ratio is further studied. Results indicate that the DT-CPA damper is effective in controlling structural vibrations and its performance is comparable to that of a conventional tuned mass damper (TMD) and even slightly superior to that of a conventional TLD system of the shallow tank configuration. The proposed concept thus holds potential for the utilization of deep tanks as energy dissipation devices with minimal interference to their usual functionality.