Engineering and Construction

In areas where strong earthquakes are  common, buildings are sometimes placed on base isolators. When signifi cant ground movement occurs, the  base isolators flex or yield to absorb a  significant portion of this movement;  as a result, the building and its sub- structure move significantly less than  they would otherwise, reducing the  forces acting on the structure and  lessening the potential for damage.

A frequently used type of base isolator is a multilayered sandwich of rubber and steel plates (Figure 2.52).

The rubber layers deform in shear  to allow the rectangular isolator to  become a parallelogram in cross section in response to relative motion  between the ground and the building. A lead core deforms enough to  allow this motion to occur, provides  damping action, and keeps the layers  of the sandwich aligned.

Figure 2.52 Base isolation.