Page 238 - Forensic Structural Engineering Handbook

7.22 CAUSES OF FAILURES

FIGURE 7.15 Severe damage to parking garage during Northridge earthquake.
(Credit: Degenkolb Engineers.)

In general, the lowest levels of buildings can receive the most serious damage during an
earthquake. Depending on the dynamic characteristics of a building and the frequency con-
tent of the earthquake, the stiffness of the lowest levels of the building may be low enough
that the mass on the upper levels is not easily excited by the higher-frequency components
of ground motions. While this can promote the survivability of the upper levels, it can be
disastrous for the lowest levels. If the lowest levels of the building are not designed to with-
stand the large differential movements that occur as the ground moves and the upper levels
remain relatively stationary, serious failures can occur (Fig. 7.16). In the most dramatic
instances, failure at the lowest levels can cause total collapse (Fig. 7.17).

FIGURE 7.16 Earthquake damage to second level of Santa Monica Hospital,
Northridge earthquake. (Credit: J. Dewey, U.S. Geological Survey.) (Source: Geologic
Hazards Photos, a compilation by the National Geophysical Data Center of the U.S.
Department of Commerce, National Oceanic and Atmospheric Administration.)