The criterion for the design of foundations of earthquake resisting structures is that the foundation system should be capable of supporting the design gravity loads while maintaining the chosen seismic energy dissipating mechanisms of the structure. The foundation system in this context includes the foundation structure, consisting of reinforced concrete construction, piles, caissons and the supporting soil.
It is evident that for this criterion a suitable foundation system for a given superstructure can be conceived only if the mechanisms by which earthquake actions are disposed of are clearly defined. In most structures inelastic deformations during large earthquakes are expected. Consequently for these structures provisions are to be made for energy dissipation, usually by flexural yielding. It is vital that energy dissipation be assigned by the designer to areas within the superstructure or within the foundation structure in such a manner that the expected ductility demands will remain within recognized capabilities of the selected components. It is particularly important to ensure that any damage that might result in the foundation structure does not lead to a reduction of strength that might affect gravity load carrying capacity.
After defining design criteria in general for foundations of earthquake resisting reinforced concrete structures, principles are set out which govern the choice of suitable foundation systems for various types of shear wall structures. The choice of foundation systems depends on whether the seismic response of the superstructure during the largest expected earthquake is to be elastic or inelastic. For inelastically responding superstructures, preferably the foundation system should be designed to remain elastic. For elastically responding superstructures, suitable foundation systems may be energy dissipating, elastic or of the rocking type. Design criteria for each of these three foundation types are suggested.