Seismic Response Reduction of Eccentric Structures Using Liquid Dampers

Abstract

The installation of vibration absorbers on tall buildings or other flexible structures can be a successful method for reducing the effects of dynamic excitations, such as wind or earthquake, which may exceed either serviceability or safety criteria. Tuned liquid column damper (TLCD) is an effective passive control device by the motion of liquid in a column container. The potential advantages of liquid vibration absorbers include: low manufacturing and installation costs; the ability of the absorbers to be incorporated during the design stage of a structure, or to be retrofitted to serve a remedial role; relatively low maintenance requirements; and the availability of the liquid to be used for emergency purposes, or for the everyday function of the structure if fresh water is used (Hitchcock et al., 1997a, 1997b). A TLCD is a U-shaped tube of uniform rectangular or circle cross-section, containing liquid. Vibration energy is transferred from the structure to the TLCD liquid through the motion of the rigid container exciting the TLCD liquid. And the vibration of a structure is suppressed by a TLCD through the gravitational restoring force acting on the displaced TLCD liquid and the energy is dissipated by the viscous interaction between the liquid and the rigid container, as well as liquid head loss due to orifices installed inside the TLCD container. Analytical and experimental researches on this type of vibration reduction approach has been conducted, in which viscous interaction between a liquid and solid boundary has been investigated and used to control vibration (Sakai et al., 1989; Qu et al., 1993). Their experiments, defining the relationship between the coefficient of liquid head loss (as well as its dependence on the orifice opening ratio) and the liquid damping, confirms the validity of their proposed equation of motion in describing liquid column relative motion under moderate excitation. A variation of TLCD, called a liquid column vibration absorber (LCVA) has also been investigated, which has different cross sectional areas in its vertical and horizontal sections depending on performance requirements (Gao and Kwok, 1997; Yan et al., 1998; Chang and Hsu, 1998; Chang 1999). Yan et al. presented the adjustable frequency tuned liquid column damper by adding springs to the TLCD system, which modified the frequency of TLCD and expended its application ranges (Yan and Li, 1999). Multiple tuned mass damper (MTMD) which consists of a number of tuned mass damper whose natural frequencies are distributed over a certain range around the fundamental frequency of the structure has been proposed and investigated (Kareem and Kline, 1995). The results showed that an optimized MTMD can be more efficient than a single optimized TMD and the sensitivity of a MTMD to the tuning ratio is diminished. A multiple tuned