9.2.2 Ties Between Foundation Elements
Foundation ties adequate for seismic forces exist where footings, piles and piers are not restrained by beams, slabs, or competent soils or rock.
For conforming buildings, the evaluator may consider this condition as mitigated, and no calculations are necessary. The deficiency is the possibility of significant differential lateral deformations of the foundations. Evaluate the lateral restraint to seismic forces provided by the foundation materials or the structural ties. For shallow foundations, evaluate the horizontal capacity of the foundation soils under seismic loading conditions (the lateral resistance of the footings due to passive resistance on affected sides of the footings plus the friction on the base of the footings) and compare to the base shear of the building. In the evaluation of base friction, consideration shall be given to the effect of the vertical component of ground motion.