FORUM State of the Art of Structural Control B. F. Spencer Jr. system is to reduce building vibration under strong winds and Nathan M. Newmark Professor, Dept. of Civil and Environmental Engi- moderate earthquake excitations and consequently to increase neering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801. comfort of occupants of the building. E-mail:
[email protected] Hybrid-control strategies have been investigated by many re- searchers to exploit their potential to increase the overall reliabil- S. Nagarajaiah ity and efficiency of the controlled structure ͑Housner et al. 1994; Associate Professor, Dept. of Civil and Environmental Engineering, Rice Kareem et al. 1999; Nishitani and Inoue 2001; Yang and Dyke Univ., Houston, TX 77005. E-mail:
[email protected] 2003; Casciati 2003; Faravelli and Spencer 2003͒. A hybrid- In recent years, considerable attention has been paid to research control system is typically defined as one that employs a combi- and development of structural control devices, with particular em- nation of passive and active devices. Because multiple control phasis on alleviation of wind and seismic response of buildings devices are operating, hybrid control systems can alleviate some of the restrictions and limitations that exist when each system is and bridges. In both areas, serious efforts have been undertaken in acting alone. Thus, higher levels of performance may be achiev- the last two decades to develop the structural control concept into able. Additionally, the resulting hybrid control system can be a workable technology. Full-scale implementation of active con- more reliable than a fully active system, although it is also often trol systems have been accomplished in several structures, mainly somewhat more complicated.