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Demolition (also known as razing, cartage, and wrecking) is the
science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...
and
engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...
in safely and efficiently tearing down of
building A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and fu ...
s and other artificial structures. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for reuse 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 wrecking ball is a heavy steel ball, usually hung from a crane, that is used for demolishing large buildings. It was most commonly in use during the 1950s and 1960s. Several wrecking companies claim to have invented the wrecking ball. An e ...
, 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 52-storey 270 Park Avenue in
New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...
, which was built in 1960 and torn down in 2019–2021 to be replaced by 270 Park Avenue.


Manual

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. In some cases a crane with a
wrecking ball A wrecking ball is a heavy steel ball, usually hung from a crane, that is used for demolishing large buildings. It was most commonly in use during the 1950s and 1960s. Several wrecking companies claim to have invented the wrecking ball. An e ...
is used to demolish the structure down to a certain manageable height. At that point undermining takes place as described above. However, crane mounted demolition balls are rarely used within demolition due to the uncontrollable nature of the swinging ball and the safety implications associated. High reach demolition excavators are more often used for tall buildings where explosive demolition is not appropriate or possible. Excavators with shear attachments are typically used to dismantle steel structural elements. Hydraulic hammers are often used for concrete structures and concrete processing attachments are used to crush concrete to a manageable size, and to remove reinforcing steel. For tall concrete buildings, where neither explosive nor high reach demolition with an excavator is safe or practical, the "inside-out" method is used, whereby remotely operated mini-excavators demolish the building from the inside, whilst maintaining the outer walls of the building as a scaffolding, as each floor is demolished. To control dust, fire hoses are used to maintain a wet demolition. Hoses may be held by workers, secured in fixed location, or attached to lifts to gain elevation. Loaders or bulldozers may also be used to demolish a building. They are typically equipped with "rakes" (thick pieces of steel that could be an I-beam or tube) that are used to ram building walls. Skid loaders and loaders will also be used to take materials out and sort steel. The technique of Vérinage is used in France to weaken and buckle the supports of central floors promoting the collapse of the top part of a building onto the bottom resulting in a rapid, symmetrical, collapse. The Japanese company Kajima Construction has developed a new method of demolishing buildings which involves using computer-controlled hydraulic jacks to support the bottom floor as the supporting columns are removed. The floor is lowered and this process is repeated for each floor. This technique is safer and more environmentally friendly, and is useful in areas of high
population density Population density (in agriculture: Stock (disambiguation), standing stock or plant density) is a measurement of population per unit land area. It is mostly applied to humans, but sometimes to other living organisms too. It is a key geographical ...
. To demolish bridges, hoe rams are typically used to remove the concrete road deck and piers, while hydraulic shears are used to remove the bridge's structural steel.
Fred Dibnah Frederick Travis Dibnah, (29 April 1938 – 6 November 2004) was an English steeplejack and television personality, with a keen interest in mechanical engineering, who described himself as a "backstreet mechanic". When Dibnah w ...
used a manual method of demolition to remove industrial chimneys in Great Britain. He cut an ingress at the base of the chimney—supporting the brickwork with wooden props—and then burning away the props so that the chimney fell, using no explosives and usually hand-operated power tools.


Building implosion

Large buildings, tall chimneys,
smokestack A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typ ...
s, bridges, and increasingly some smaller structures may be destroyed by building implosion using explosives. Imploding a structure is very fast—the collapse itself only takes seconds—and an expert can ensure that the structure 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. One significant danger is from flying debris, which, when improperly prepared for, can kill onlookers. Another dangerous scenario 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. A third danger comes from air overpressure that occurs during the implosion. If the sky is clear, the
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
, a wave of energy and sound, travels upwards and disperses, but if cloud coverage is low, the shock wave can travel outwards, breaking windows or causing other damage to surrounding buildings. Controlled implosion, being spectacular, is the method that the general public often thinks of when discussing demolition; however, it can be 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 leveled around the world. At and , the
J. L. Hudson Department Store and Addition The J. L. Hudson Building ("Hudson's") was a department store located at 1206 Woodward Avenue in downtown Detroit, Michigan. It was constructed beginning in 1911, with additions throughout the years, before being "completed" in 1946, and named af ...
is the tallest steel framed building and largest single structure ever imploded.


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 Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
that can form deadly projectiles, and insulation that can scatter over a wide area. Non-load bearing partitions and
drywall Drywall (also called plasterboard, dry lining, wallboard, sheet rock, gypsum board, buster board, custard board, and gypsum panel) is a panel made of calcium sulfate dihydrate (gypsum), with or without additives, typically extruded between thic ...
are removed. Selected columns on floors where explosives will be set are drilled and
high explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
such as nitroglycerin,
TNT Trinitrotoluene (), more commonly known as TNT, more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene, is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reagen ...
,
RDX RDX (abbreviation of "Research Department eXplosive") or hexogen, among other names, is an organic compound with the formula (O2N2CH2)3. It is a white solid without smell or taste, widely used as an explosive. Chemically, it is classified as a ...
, or C4 are placed in the holes. Smaller columns and walls are wrapped in
detonating cord Detonating cord (also called detonation cord, detacord, detcord, primer cord, or sun cord) is a thin, flexible plastic tube usually filled with pentaerythritol tetranitrate (PETN, pentrite). With the PETN exploding at a rate of approximately ...
. The goal is to use as little explosive as possible so that the structure will fail in a
progressive collapse Progressive collapse is the process where a primary structural element fails, resulting in the failure of adjoining structural elements, which in turn causes further structural failure. Progressive collapses may be accidental, as the result of d ...
, and therefore only a few floors are rigged with explosives, so that it is safer due to fewer explosives, and costs less. The areas with explosives are covered in thick
geotextile Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in two basic forms: woven (r ...
fabric and fencing to absorb flying debris. Far more time-consuming than the demolition itself is the clean-up of the site, as the debris is loaded into trucks and hauled away.


Deconstruction

An alternative approach to demolition is the deconstruction of a building with the goal of minimizing the amount of materials going to landfills. This "green" approach is applied by removing the materials by type material and segregating them for reuse or
recycling Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
. With proper planning this approach has resulted in landfill diversion rates that exceed 90% of an entire building and its contents in some cases. It also vastly reduces the CO2 emissions of the removing of a building in comparison to demolition. The development of plant and equipment has allowed for the easier segregation of
demolition waste Demolition waste is waste debris from destruction of buildings, roads, bridges, or other structures. Debris varies in composition, but the major components, by weight, in the US include concrete, wood products, asphalt shingles, brick and clay ti ...
types on site and the reuse within the construction of the replacement building. On site crushers allow the demolished concrete to be reused as type 1 crushed aggregate either as a piling mat for ground stabilization or as aggregate in the mixing of concrete. Timber waste can be shredded using specialist timber shredders and composted, or used to form manufactured timber boards, such as MDF or chipboard. Safety is paramount; a site safety officer is usually assigned to each project to enforce all safety rules and regulations.


See also

* * *Excavator (Protection of excavators used for demolition) * (military tactic) * * * (UK) * * *


References


External links

{{Authority control Building engineering