Demolition
From Wikipedia, the free encyclopedia
- For other uses, see Demolition (disambiguation).
Demolition is the opposite of construction: the tearing-down of buildings and other structures. It contrasts with deconstruction, which is the taking down of a building while carefully preserving valuable elements for re-use. The tallest demolished building was the 47-story Singer Building of New York City, which was built in 1908 and torn down in 1967-1968 to be replaced by One Liberty Plaza.
For most 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.
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[edit] Building implosion
Large buildings, tall chimneys, and increasingly some smaller structures may be destroyed by building implosion using explosives. Imploding a building is very fast — the collapse itself only takes seconds — and an expert can ensure that the building falls into its own footprint, so as not to damage neighboring structures. This is essential for tall structures in dense urban areas. Any error can be disastrous, however, and some demolitions have failed, severely damaging neighboring structures. The greatest danger is from flying debris which, when improperly prepared for, can kill onlookers. Even more dangerous is the partial failure of an attempted implosion. When a building fails to collapse completely the structure may be unstable, tilting at a dangerous angle, and filled with un-detonated but still primed explosives, making it difficult for workers to approach safely. While controlled implosion is the method that the general public often thinks of when discussing demolition, it is extremely dangerous and is only used as a 'last resort' when other methods are impractical or too costly. The destruction of large buildings has become increasingly common as the massive housing projects of the 1960s and 1970s are being levelled around the world. At 439 feet and 2.2 million square feet, the J.L. Hudson Department Store and Addition is the tallest steel framed building and largest single structure ever imploded.[1]
[edit] Preparation
It takes several weeks or months to prepare a building for implosion. All items of value, such as copper wiring, are stripped from a building. Some materials must be removed, such as glass that can form deadly projectiles, and insulation that can scatter over a wide area. Non-load bearing partitions and drywall are removed.[2] Selected columns on floors where explosives will be set are drilled and nitroglycerin and TNT are placed in the holes. Smaller columns and walls are wrapped in detonating cord. The goal is to use as little explosive as possible; only a few floors are rigged with explosives. The areas with explosive are covered in thick geotextile fabric and fencing to absorb flying debris.[2] Far longer than the demolition itself is the clean-up of the site, as the debris is loaded into trucks and hauled away.
[edit] Traditional demolition
Prior to any demolition activities a multitude of steps needs to take place including but not limited to performing asbestos abatement, obtaining necessary permits and submit necessary notifications, disconnection of all utilities, rodent baiting and 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 means of 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 falls in the desired manner and direction. The walls are typically undermined at a building's base, but this is not always the case as building designs may dictate otherwise. Safety and cleanup considerations are also taken into account in determining how the building is undermined and ultimately demolished.
In some cases a crane with a wrecking ball is utilized to demolish the structure down to a certain manageable height. At that point undermining takes place as described above in first paragraph.
In order to control dust, fire hoses will be utilized to maintain a wet demolition. Hoses may be held by workers, secured in fixed location, or attached to lifts to gain elevation.
Loaders or dozers may also be used to demolish a building. These loaders and bulldozers are typically equipped with "rakes" (which are thick pieces of steel which could be an I-Beam or thick steel tube) that is used to ram building walls. Skid loaders and loaders will also be used to load materials out and sort steel.
Safety should always be paramount on each project. A site safety officer should be assigned to each project to enforce all OSHA and client specific safety rules and regulations.
[edit] Gallery
 An excavator is used to demolish a barn. |
 With heavy equipment, demolition of a house is a two man job that can be completed in a day or two. |
 Rotational Hydraulic shears and standard reinforced bucket attachments are common demolition tools. |
 High Reach Demolition Excavator. |
 Grain elevator demolition. Minneapolis, Minn.; United States. |
