Study of a Tank-Pipe Damper System for Seismic Vibration Control of Structures A.D. Ghosh & P.C. Saha Bengal Engineering and Science University, Shibpur, Howrah, India B. Basu Trinity College Dublin, Dublin 2, Ireland SUMMARY: This paper examines the theoretical model of a tank-pipe (T-P) damper, consisting of two tanks and a connecting pipe with orifice(s), which can control three modal responses of the structure. A transfer function formulation of a base-excited multi-degree-of-freedom (mdof) structure with attached T-P damper is presented. Numerical studies in the frequency domain are carried out to demonstrate the effectiveness of the proposed damper. The supplemental equivalent viscous damping and optimal orifice damping coefficient are studied. Comparisons are made with the liquid column damper (LCD). Results indicate that the T-P damper has lower performance sensitivity and greater robustness. It provides a better option than the LCD for the reduction of responses with significant higher mode participation. Moreover, for ground motions with energy content that excite modes other than the mode to which the LCD is tuned, the tank-pipe damper achieves considerable vibration suppression while the LCD may be rendered practically ineffective. Keywords: tank-pipe damper, seismic excitation, transfer function, LCD 1. INTRODUCTION Liquid dampers are popular passive control devices for civil engineering structures due to their low capital and maintenance costs, easy installation, effectiveness even in low vibration amplitudes and for the versatile use of the water in the damper such as for firefighting, etc. There are chiefly two types of liquid dampers, namely sloshing dampers and column dampers. Kareem and Sun (1987) and Fujino et al. (1992) were amongst those who carried out pioneering work on the liquid sloshing damper and expounded the importance of having shallow liquid height and of tuning the sloshing frequency to the structural fundamental frequency. Some researchers like Koh et al. (1994, 1995) and Banerjee et al. (2000) demonstrated the effectiveness of the device in controlling the seismic response of structures. Tait et al. (2008) investigated both unidirectional as well as bidirectional tuned liquid dampers (TLD) and provided performance charts for the same. Tait and Deng (2010) studied different tank geometries of the TLD and reported that a horizontal-cylindrical TLD is the most robust. The liquid column damper (LCD), which dissipates energy by the movement of an oscillatory column of liquid through orifice(s) provided in the cross section of a U-shaped container, scores over the sloshing damper due to its higher volumetric efficiency, consistent performance over a wide range of excitation levels and a very specific damping mechanism. Originally proposed by Saoka et al. (1988) and experimentally verified by Sakai et al. (1989), it has been extensively investigated for the mitigation of wind-induced vibration such as by Xu et al. (1992), Balendra et al. (1999), Shum and Xu (2004), Wu et al. (2005) and Min et al. (2009), amongst others. The applicability of this device as a seismic vibration control device has been explored by Sun (1994), Won et al. (1996), Reiterer and Ziegler (2005), Ghosh and Basu (2008), etc. Studies have also been undertaken on several variations of the conventional LCD, with either different geometric configuration such as the V-shaped LCD by Gao and Kwok (1997) or with non-uniform column cross-section called the liquid column vibration absorber (LCVA) by Hitchcock et al. (1997), Wu et al. (2009), Konar and Ghosh (2010), etc., with encouraging results.