Page 240 - Forensic Structural Engineering Handbook

7.24 CAUSES OF FAILURES

FIGURE 7.18 Loma Prieta Damage to upper-level of Clay Building,
Oakland, California. (Credit: C. Stover, 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.)

The resulting eccentricities between vertical loads and their supporting elements tend to
amplify overturning moments. Building response to seismic loads, with large inelastic dis-
tortions an inherent characteristic, normally involves greater potential for significant P-
delta response than does elastic building response to wind loads. The amplification of
moments can be unstable when the inelastic frame stiffnesses and strengths cannot resist
the amplified movements and forces.
Structures with insufficient internal ties can fail when structural distortions exceed
movement capacities of supports. Beams sometimes drop from their supports because con-
nections have insufficient strength to resist forces due to differential movements at