ABSTRACT
Modern tall building are more lighter and slender with a lower natural frequency and damping ratio, so these tall buildings are more sensitive to windinduced vibration. One way of mitigating such an excessive wind-induced vibration of tall buildings is by using vibration control devices. Passive Tuned Mass Damper (PTMD) is a classical vibration control device, which consists of a mass, a spring, and a damper supported on the main vibrating structure (Den Hartog 1956). The original idea of PTMD was proposed by Frahm in 1909, who invented a vibration control device called a vibration absorber using a spring-supported mass without damper (Frahm 1909). It was effective when the absorber’s natural frequency was close to the excitation frequency. However, it was difficult tuning the absorber’s natural frequency to the excitation frequency. This control device was improved by introducing a damper in the spring-supported mass (Ormondroyd et al. 1928). Later, Den Hartog derived optimum tuning frequency and damping ratio for the undamped main structure under harmonic load (Den Hartog
was called Active Tuned Mass Damper (ATMD) (Housner et al.1997). In 1972, Yao introduced the modern control theory into vibration control of a civil engineering structure, and many auxiliary control devices combining with modern optimal control theory have been developed for mitigating the excessive wind-induced vibrations of tall buildings (Yao 1972). One way of ATMD design for reducing wind-induced vibration of tall building using assumed deterministic harmonic wind loading was presented by Chang and Soong in 1980 (Chang et al. 1980). That was the first active control study for mitigating wind-induced vibration of tall buildings with ATMD using a Linear Quadratic Regulator (LQR) controller. Since then, many studies have been advanced for obtaining optimal control force for reducing wind-induced vibration of tall buildings on the basis of the modern optimal control technique (Ankireddi et al. 1996, 1997). However, the fact that ATMD is superior to PTMD reducing wind-induced vibration of tall buildings is still question (Ricciardelli et al. 2003). From the viewpoint of the modern optimal control theory, fluctuating across-wind load acting on a tall building can be treated as a stationary random process, and a constant power spectrum could be considered as a system noise. Then, many advanced studies for mitigating wind-induced vibration of tall buildings on the basis of the modern optimal control theory, including Linear Quadratic Gaussian (LQG), H2 and H⊥ have been developed, and a number of tall buildings are currently implemented with active control device systems (Yang et al 2002, 2003). Nishimura and Wang et al. pointed out that the disadvantage of a single PTMD is its error in tuning the natural frequency of PTMD to that of the main structure and fitting the optimum damping ratio of PTMD. The size restriction of PTMD limits the vibration control effect (Nishimura et al.1994, 1998, Wang et al. 1999).
