9.2.1 Overturning

The ratio of the effective horizontal dimension, at the foundation level of the seismic-resisting system, to the building height (base/height) exceeds 1.4 A_v.

For conforming buildings, the evaluator may consider this condition as mitigated, and no calculations are necessary. The deficiency is the concentration of seismic inertial response into narrow elements by the seismic-resisting system, which may overcome the ability of the foundation elements, either structure or soil, to provide adequate resistance. For shallow foundations, evaluate the shear and moment capacity of the foundation elements for adequacy to resist calculated seismic forces. Evaluate the vertical bearing pressure of the soil under seismic loading conditions due to the total gravity and overturning loads and compare to two times the allowable static-bearing pressure. For deep foundations, evaluate the ultimate vertical capacity of the pile or pier under seismic loads. Compare the foundation capacity to the gravity loads plus the overturning loads.