Figure : Friction controllable bearing tested by Feng.
  1. HYBRID MASS DAMPER
The hybrid mass damper (HMD) is the most common control device employed in full-scale civil engineering applications. The HMD is a combination of a TMD and an active control actuator. The ability of this device to reduce structural responses relies mainly on the natural motion of the TMD. The forces from the control actuator are employed to increase the efficiency of the HMD and to increase its robustness to changes in the dynamic characteristics of the structure. The energy and forces required to operate a typical HMD are far less than those associated with a fully active mass driver system of comparable performance.
  1. HYBRID BASE ISOLATION
Another class of hybrid control systems that has been investigated by a number of researchers is found in the active base-isolation system, consisting of a passive base-isolation system combined with a control actuator to supplement the effects of the base-isolation system. Base-isolation systems have been implemented on civil engineering structures worldwide for a number of years because of their simplicity, reliability, and effectiveness. Excellent review articles of base-isolation systems are presented by Kelly (1981, 1986), Buckle and Mayes (1990), and Soong and Constantinou (1994). However, base-isolation systems are passive systems and are limited in their ability to adapt to changing demands for structural response reduction. With the addition of an active control device to a base-isolated structure, a higher level of performance can be potentially achieved without a substantial increase in the cost (Reinhorn et al. 1987), which is very appealing from a practical viewpoint. Since base isolation by itself can reduce the inter-story drift and the absolute acceleration of the structure at the expense of large absolute base displacement, the combination with active control is able to achieve both low inter-story drift and, at the same time, limit the maximum base displacement with a single set of control forces. A robust control for uncertain linear base-isolated structures was proposed by Kelly et al. (1987), and more recently by Schmitendorf et al. (1994) and Yoshida et al. (1994).
  1. LOCK UP DEVICES
  2. COMMONLY USED SEISMIC PROTECTION SYSTEMS IN BANGLADESH
Chapter 3