Figure : Working Process of Active Protection System[12].
  1. ACTIVE TUNED MASS DAMPER
One of the earliest approaches to active control of vibrations in structures has been Active Tuned Mass Damper (ATMD) systems. This system is also known as an Active Mass Driver (AMD). In an ATMD system, an actuator placed between the structure and the TMD system applies a computed force in real time. The tuned mass damper has been suggested to be connected to electrohydraulic servomechanisms to form an active mass damper. Both the active control forces and the inertia forces resulting from motions of the mass damper can be used beneficially for reducing the dynamic response of a structures. Such a control system has been shown to be very efficient for tall buildings under strong earthquake loads. Out of these, active mass/tuned mass dampers have been implemented for the response reduction of tall buildings in controlling wind-induced vibrations. Yamamoto et al. [35] present the performance results of ATMD systems installed in four actual steel-frame high-rise buildings in Japan, ranging in height from 58.0 to 189.7 m (11–34 stories). The ATMD systems for three of the buildings utilized existing masses, such as ice thermal storage tanks (used for air conditioning) and a heliport as the controlling masses. To verify the control systems, they carried out forced vibration tests on each building before completion, using the ATMD system itself to shake the building. After the ATMD system shook the building for a period of 10 s, it was activated to suppress the response of the building. The authors also monitored the response of the completed buildings under minor seismic events and wind loading. Their results showed that the installed ATMDs were effective at controlling the response of the buildings. The majority of research published on TMD systems is limited to a single ATMD. A few researchers have advocated the use of multiple ATMDs in a given structure. Li et al. [40] advocate the use of multiple ATMDs for control of vibrations due to ground motions and show that several smaller ATMDs perform better than a single large ATMD. Ikeda et al. [39] discuss the performance of an ATMD system actually installed in a ten-story, steel-frame building in Tokyo in 1989. The system utilizes two AMTDs to control both lateral and torsional vibrations and the LQR control algorithm. Since its installation, the building has been subjected to actual earthquake and typhoon wind loadings, with 26% and 11% reductions in lateral and torsional vibrations during earthquakes, and a 33% reduction in peak response due to wind loadings.