Text 1. Building Construction

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The construction of the homes and buildings in which people live and work has been a major industry ever since early human beings first made huts of sticks, mud, or rocks. Methods of building construction have been constantly improved since those first crude structures. Modern skyscrapers can be built within a year or two. Prefabricated buildings, with their various parts made in factories by assembly-line methods, can be built in a day or two, but are rarely as durable as traditionally made buildings. 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 may also be an important factor. In some areas, buildings have to be constructed to withstand earthquake shocks. Foundations are the chief means of supporting a building. They carry both the dead and live loads. There are three main types of foundations: (1) spread, (2) pier, and (3) pile.

Spread foundations are long slabs of reinforced concrete that extend beyond the outer edges of the building. Such foundations are not so 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. Any such settlement 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 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 60 metres to a layer of solid soil or rock. Workers can tell when the columns reach their proper depth by the number of blows the pile driver needs to drive the columns a few centimetres deeper. These columns transmit the building load to the supporting soil. Most skyscrapers are supported by rock foundations.

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