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Part of a structural system that supports and anchors the superstructure of a building and transmits its loads directly to the earth. To prevent damage from repeated freeze-thaw cycles, the bottom of the foundation must be below the frost line. The foundations of low-rise residential buildings are nearly all supported on spread footings, wide bases (usually of concrete) that support walls or piers and distribute the load over a greater area. A concrete grade beam supported by isolated footings, piers, or piles may be placed at ground level, especially in a building without a basement, to support the exterior wall. Spread footings are also usedin greatly enlarged formfor high-rise buildings. Other systems for supporting heavy loads include piles, concrete caisson columns, and building directly on exposed rock. In yielding soil, a floating foundationconsisting of rigid, boxlike structures set at such a depth that the weight of the soil removed to place it equals the weight of the construction supportedmay be used.
This entry comes from Encyclopædia Britannica Concise. For the full entry on foundation, visit Britannica.com.