building foundations
designed to provide buildings with support and stability, foundations are the first structural components install in most construction projects, spread-footing foundations are a common economical choice for project built on stablle ground. friction piles distribute weight along their entire length, unlike caisson piers, which transmit the buildin's load to the stable bedrock that only the ends of the piers contact. mat foundation are reinforced concrete slabs used when building loads are relatively large , and ground conditions are unstable; these foundations carry the downward load of a building as a unit 'floating' on the soil.
a mat, or raft, which is a single slab over the entire foundation bed, is often used. a bearing wall around the outer limits of the structure is supported by a continuous footing. separate footings may be use to support columns.
when the surface soil stratum is too weak to support the structure, piles and piers may be used to transfer the weight to stronger substrata. concrete piles are either pre-cast or cast insitu. the pre-cast type is formed of steel bars set in concrete, which is the driven into the soil. to construct the cast insitu type, a hole is first made into the soil at the desired location and then filled with concrete. it may or not be reinforced. this type is often preferred because it takes less time and requires no molding.
there are other types of strctures used in building bridges, piers, and docks.examples of these are the open caisson, the pneumatic caisson, the sheet piling, and the cofferdam.
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