Ground Motions and Structures - Earthquake Engineering for Structural Design - page 355

Ground Motions and Structures 355

8.5.6Base-isolatedSystems

Base isolation is believed to be the most powerful tool in earthquake engineering,
pertaining to the passive structural vibration technologies. It is meant to enable a
building structure to survive a potentially devastating earthquake without important
damages (Wikipedia, nd).
Conventional earthquake-resistant structural systems, presented in the previous
section, are considered fixed at the ground level. Their earthquake resistance is derived
from the ability to absorb seismic energy in specially designed regions of the
structures, the so-called “dissipative zones”, such as at the beam ends near beam-
column joints. These regions should be capable of deforming into inelastic range and
sustaining large reversible cycles of plastic deformations, all without losing strength
and stiffness. These inelastic activities also mean large deformations in primary
structural members, resulting in a significant amount of damage in structural and non-
structural elements. Contrary to this behavior, the base-isolation systems provide the
superstructure to be isolated from the foundation by means of certain devices, which
reduce the ground motions transmitted to the structure (Fig. 8.53). These devices
absorb the seismic input energy by adding significant damping. In comparison with the
conventional fixed-base systems, this technique considerably reduces the structural
response as well as the damage to structural and non-structural elements (Rai, 2000).

Figure 8.53 Base-isolated systems (after Rai, 2000)

(a)