Demolition

Demolition is the tearing down of buildings and other man-made structures. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use purposes.

For small buildings, such as houses, that are only two or three stories high, demolition is a rather simple process. The building is pulled down either manually or mechanically using large hydraulic equipment: elevated work platforms, cranes, excavators or bulldozers. Larger buildings may require the use of a wrecking ball, a heavy weight on a cable that is swung by a crane into the side of the buildings. Wrecking balls are especially effective against masonry, but are less easily controlled and often less efficient than other methods. Newer methods may use rotational hydraulic shears and silenced rock-breakers attached to excavators to cut or break through wood, steel, and concrete. The use of shears is especially common when flame cutting would be dangerous.

The tallest planned demolition of a building was the 47-story Singer Building in New York City, which was built in 1908 and torn down in 1967–1968 to be replaced by One Liberty Plaza.

Before any demolition activities can take place, there are many steps that must be carried out beforehand, including performing asbestos abatement, removing hazardous or regulated materials, obtaining necessary permits, submitting necessary notifications, disconnecting utilities, rodent baiting and the development of site-specific safety and work plans.

The typical razing of a building is accomplished as follows:

Hydraulic excavators may be used to topple one- or two-story buildings by an undermining process. The strategy is to undermine the building while controlling the manner and direction in which it falls. The demolition project manager/supervisor will determine where undermining is necessary so that a building is pulled in the desired manner and direction. The walls are typically undermined at a building's base, but this is not always the case if the building design dictates otherwise. Safety and cleanup considerations are also taken into account in determining how the building is undermined and ultimately demolished.

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