Slab-on-grade or floating slab foundations are a structural engineering practice whereby the concrete slab that is to serve as the foundation for the structure is formed from a mold set into the ground. The general purpose of a strap footing is alike to those of a combined footing, where the spacing is possibly limited and/or the columns are adjacent to the property lines.ĭiagrams of the types of shallow foundations. Conversely, when the load among the columns is unequal, the combined footing should be trapezoidal.Ī strap footing is when individual columns are connected to one another with the use of a strap beam. When the load among the columns is equal, the combined footing may be rectangular. Also, when property lines make isolated footings eccentrically loaded, combined footings are preferred. Utilized when the spacing of the columns is too restricted, that if isolated footing were used, they would overlap one another. When more than one column shares the same footing, these are called combined footing. This type of footing is used when the structural load is relatively low, columns are widely spaced, and the soil's bearing capacity is adequate at a shallow depth. Sometimes, an isolated footing can be sloped or stepped at the base to spread greater loads. Generally, each of its columns gets its footing to transmit and distribute the load of the structure towards the soil underneath. Isolated footing Īlso called single-column footing, it is a square, rectangular, or circular slab that supports the structural members individually. When the soil is so soft that not even friction piles will support the building load, these types of foundation are the final option and makes the building behave like a boat: obeying Archimedes' principle, buoyed up by the weight of the earth displaced in creating the foundation.Detail Section of a strip footing and its wall. The earliest precursor to the modern version may be the concrete rafts developed for the building of Millbank Prison in 1815 by Robert Smirke.įor a floating raft foundation – or simply 'floating foundation' – the foundation has a volume such that, if that volume filled with soil, it would be equal in weight to the total weight of the structure. It was a necessary innovation in the development of tall buildings in the wet soil of Chicago in the 19th century, when it was developed by John Wellborn Root who came up with the idea of interlacing the concrete slab with steel beams. JSTOR ( June 2019) ( Learn how and when to remove this template message)įloating raft is type of land-based foundation that protects against settlement and liquefaction of soft soil from seismic activity.

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Floating foundation wikipedia