Foundation (architecture)
From Free net encyclopedia
A foundation is a structure that transmits loads from a building or road to the underlying ground. A footing is a slab element that acts as the foundation, transferring loads from the superstructure to the ground.
Image:Leaning-tower-of-pisa-alternate.jpg Most foundations extend underground, and the foundations of large buildings often penetrate to the bedrock. One common type of foundation consists of walls that extend below the frost line and transfer the weight to wider footings. Other kinds of foundations include Slab-on-grade foundations, pier and beam foundations and piles.
The primary dangers to a foundation are movement and uneven support. Change in ground water table is a common cause of foundation failure. Also flowing water can remove supporting soil from underneath a bridge foundation and freezing water can heave the supporting soil in one direction and then in the other direction when it thaws.
Changes in soil moisture can cause 'reactive' clay soil to swell and shrink. This swelling can vary across the footing due to seasonal changes or the effects of vegetation removing moisture. The variation in swell can cause a footing sitting on the reactive foundation soil to distort, cracking the structure over it. This is a particular problem for house footings in semi-arid climates such as South Australia, Southwestern USA, Israel, and South Africa where wet winters are followed by hot dry summers. Raft slabs with inherent stiffness have been developed in Australia with capabilities to resist this movement.
When heavy structures are built in arctic areas where the ground is permanently frozen, special refrigeration units must be used to keep the pressure of the structure from melting the supporting soil.
Ground compaction
The final "foundation" being the ground, it may help to understand how compaction tests are done.
A sample of dirt is baked to remove moisture. A weight is then dropped from a set height onto this dirt. A small amount of moisture is added, homogeneously, and the weight is again dropped from the set height. The process is repeated until the soil stops compacting and instead begins to deform to encompass the weight. Foundations should be poured upon dirt which has an optimal content of moisture for that particular area, compacted in layers.
See also
de:Gründung (Bauwesen) es:Cimentación fi:Perustus nl:Fundering pl:Fundament sv:Fundament zh:基础