Ground Motions and Structures - Earthquake Engineering for Structural Design - page 358

358 Earthquake Engineering for Structural Design

8.5.8Active Control Systems

The philosophy of the earthquake-resistant system mentioned until now is based on a
passive response to the earthquake action. In contrast, there is another expanding class
of systems, which are referred to as smart or active control systems (Fig. 8.55) . These
systems differ from the passive systems in the sense that they control the seismic
response through appropriate adjustments within the structure, as far as the seismic
excitation changes. In other words, active control systems introduce elements of
dynamism and adaptability into the structure, thereby augmenting the capability to
resist exceptional earthquake loads. A majority of the proposed techniques involves
adjusting lateral strength, stiffness and dynamic properties of the structure during the
earthquake to reduce the structural response. In spite of this very promising solution to
control the structural response, many serious problems exist with respect to the time
delay in control actions, structural nonlinearity and very high operational costs (Rai,
2000).
The basic configuration of an active control system consists of three elements: (i)
Sensors to measure external excitation and/or structural response; (ii) Computer
hardware and software to compute control forces on the basis of observed excitation
and/or structural response; (iii) Actuator to provide the necessary control forces.

Figure 8.55 Active control systems (after Rai, 2000)