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Text A. Elements of a Building. Types of Foundation
The first houses were built for the purpose of protecting their owners from the weather and, therefore, were very simple - a roof to keep off the rain or snow, and walls to keep out the wind.
The building erected now can be divided into two broad classifications: they are either for housing or for industrial purpose.
As far as the material is concerned, the building can be divided into stone (or brick), wood and concrete types. The brick is an artificial material made of clay then burnt to harden it. The natural stone is used for footing and foundations for external walls carrying the load. The buildings made of stone or brick are durable, fireproof and have poor heat conductivity.
Materials and structural forms are combined to make up the various parts of a building, including foundations, load-carrying frame, skin and interior constructions. The building also has mechanical and electrical systems, such as lifts and escalators, heating and cooling systems, and lighting systems.
A building has two main parts, the substructure (the part below ground) and the superstructure (the part above ground). The substructure is usually called the foundation. It includes the basement walls, even though these may extend above the ground.
Both the substructure and the superstructure help to support the load (weight) of the building. The dead load of a building is the total weight of all its parts. The live load is the weight of the furniture, equipment, stored material, and occupants of a building. In some regions, the wind load of a building is important if the structure is to withstand storms. The snow load and earthquake shocks may also be important factors.
Foundations are the chief means of supporting a building. They carry both the dead and live loads. There are four main types of foundations: (1) spread, (2) pier, (3) pile, and (4) mat, or raft.
Spread foundations are long sections and rectangular slabs of reinforced concrete that extend beyond the outer edges of the building and under its walls and columns. Such foundations are not as firm as those based on solid rock. The footing areas in contact with the soil must be of sufficient size to spread the load safely over the soil and to avoid excessive or uneven settlement that would cause walls to crack or doors to bind.
Pier foundations are heavy columns of concrete that go down through the loose topsoil to a bed of firm rock. This bed may also be sand, gravel, or firm clay. If the bed consists of firm clay, the pier is usually belled out (enlarged) at the base, to increase the bearing area.
Pile foundations are long, slender columns of steel, concrete, or wood. Machines called pile drivers hammer them down as deep as 200 feet (61 meters) to a layer of solid soil or rock. These columns transmit the building load to the supporting soil. Most skyscrapers are supported by rock foundations.
Mat foundations, also called raft foundations, are thick slabs of reinforced concrete that span the whole area beneath a building. They are normally used in poor soil conditions where it is not possible or economical to drive piles or piers down to good soil or rock. In effect, they enable the building to "float" on the soft soils.
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