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Critical Sequences in Demolition

Introduction

The definition of the phrase ‘demolish’ is deliberate and controlled collapse of a structure. In the late 1970’s Fred Dibnah became the most well known steeplejack in The British Isles when his work on demolishing large chimneys without the requirement of explosives was presented on Television. Fred was an entertaining character and became popular as an authority on repairing tall chimneys, so when it came to knocking them down he knew the way to acheive it. He would have to cut an niche at the base of the chimney, and then place wooden props to underpin the structure. By means of properly setting the props, the chimney would fall in the correct place when the wood was set alight and burned away. Once he was almost killed because he miscalculated somewhat, demonstrating how dangerous demolition work really is.

The particular phrase to demolish only came into being in 1570, and was used from then on to mean the deliberate taking down or destroying of a building or structure. Though in reality the task of demolition, in some manner or other, has been occurring for millenia. Buildings were demolished either by natural disruptions of the Earth’s crust or in the course of battles or attacks on communities for as long as there have been buildings. The leftover ruins were taken away and rebuilt or used for other properties close by and must be early types of recycling.

Preserving the Past – Preparing the Future.

To protect Britain’s history of agriculture the farm land between the built up areas of the villages and towns is shielded from expansion of urban sprawl. This farm land is known as Green Belt and is preserved for farming that is fundamental to the continuing economy of the country. By safeguarding the Green Belt, urban areas are being squeezed for the provision of housing, so developers end up being much more creative to uncover suitable sites.

Great Britain is a country with an extremely dense population per square mile. The amount of land available for development is small in comparison to other countries. Consequently there is always a healthy need for space on which to build. Taking down aged and abandoned structures and replacing them with new is one method to attempt to counter this general shortage.

Land which may be disused industrial and commercial sites, but could be polluted with hazardous waste or pollution, are called Brownfield sites. When the land has been cleaned up they can be potentially valuable for redevelopment. Both Glasgow and South Wales constructed gardens out of old industrial sites and installed Shopping centres to attract tourists and generate income.

Greyfield sites are distinct to Brownfield sites in that they don’t have the environmental concerns of toxic waste. The expression greyfield comes from the massive areas of asphalt which often had once been car parks of industrial urban buildings. Their advantage is incorporated in the fact that the facilities like highways, electricity, water, sewerage, and gas is already available. These kinds of urban areas that become under-utilised or abandoned and are valuable due to the fact they require little or no remedial work to be developed. Cities including Leeds and Manchester have experienced an enormous programme of changing the existing warehouses or factories into flats, shops and restaurants, retaining the original shell and refurbishing the interior into valuable accommodation.

The Demolition Process

Structures designated to be demolition ready, must have the following items considered.

• The design type and physical size of the structure.
• What elements have re-use value?
• What will the cleared site’s re-use be for?
• Where are the waste by-products likely to be disposed?
• What steps need to be made with regards electricity, water, sewerage and gas mains.

Hydraulic excavators and bulldozers may be used to undermine the walls at the foundation, so that the structure will topple; at the same time managing the manner and course of the fall. Questions of safety are extremely important, and clean-up plans are also considered when deciding how the property is going to be demolished.

Old fashioned Demolition

In the past the standard manner of demolishing a building was incredibly crude. Once all the services were shut off, the men and equipment would go in and simply knock down the walls. Then the entire building would fall and the resulting rubble could be piled on lorries and be dumped in landfill sites. Concrete footings were broken up by pneumatic drills and then the site would be cleaned of rubbish ready for the new work to start. However today demolition activities are at the mercy of rigorous planning, health and safety and monitoring polices and so are heavily controlled by the local council. How a building is constructed will mean that one part depends on the other for solidity and sturdiness. For instance the roof of a building is not really fastened down other than fixing tiles with nails to stop them slipping. The roof stays in position with its own weight because the beams are laid on the top of the walls as opposed to being fixed into them like they once were for much older homes. The cross beams and purlins then connect the entire thing together to tie down the frame of the roof. To this slats are laid as a frame for laying on the tiles or slates. Other areas of a building may also be interdependent so in terms of demolition these issues are taken into consideration in the sequence of deconstruction. In this way, like Fred Dibnah you need to be an expert in construction to know how to perform the deconstruction.

Deconstruction and Recycling

The modern method of demolishing buildings is known as deconstruction – an environmentally friendly approach. Landfill sites are in limited supply therefore the aim when demolishing a building is to diminish the amount of waste materials leftover.

Modest structures like two or three storey homes may be taken apart quite simply. The work can be a painstaking task of dismantling manually – brick by brick – or beam by beam but by proceeding very carefully expensive materials are preserved for re-use. The value of deconstruction is that 90% or even more of waste material is prevented from going into landfill sites and reclaimed resources can be re-used and recycled for upcoming buildings. The farmer opposite my family home sold his barns inside the farm yard for construction; when the contractor demolished the barns he cleaned up the bricks and reused them to make the wall around the farmhouse hence retaining the character of the farm.

Contemporary techniques and equipment allows demolition companies to efficiently segregate waste product types on or off-site. Quality materials are recycled and re-used whenever practical in the new construction making considerable reductions in project costs not to mention being good for the planet.

Concrete can now be quickly broken up with a giant guillotine.

Creating 6f2 recycled material is extremely cost effective as it avoids the expense of hauling the building waste to landfill sites. Crushed material from the demolition can be used as a sub-base for the new building foundations or used on other sites where construction is underway.

Copper pipes, lead, roof tiles or slates, floor tiles, wiring and exterior doors, and wood panelling are useful items which might be preserved for recycling to be re-used. Many specialist businesses offer reclaimed old or traditional building products in the majority of towns and cities.

Taller Structures

Tower blocks and chimneys are the kind of tall buildings which might need to be demolished. The demolition of tall buildings necessitates skilled procedures. The tallest building to be demolished lawfully was in 1967/8 for the Singer Building in New York. The fall of the World Trade Centre after the 9/11 assault in 2001 demonstrates the terrible devastation that develops when the demolition is out of control and haphazard.

In the demolishing of high properties and big structures a wrecking ball on a crane can be employed, but is hardly ever used because the swinging ball is rather uncontrollable. The closeness of other buildings is often a determining factor which inhibits the usage of explosives to implode a tall building. So ‘High Reach’ demolition excavators are widely-used where other solutions will not be possible to demolish the top portion of a tall building. Once it is down to a manageable height demolition can continue in the usual way. The various methods of demolishing tall buildings are by implosion using explosives, controlled collapse and piecemeal. To control the dust produced in demolition, water hoses and spray equipment are sometimes used and then it is called a wet demolition.

Explosions

The use of explosives in demolition is extremely specialist work and getting it wrong could be devastating. If for instance there exists atmospheric pressure from low cloud above the implosion site, the shockwave may spread outwards instead of upwards causing the wave of energy and sound to break glass windows. If an implosion is not prepared correctly the danger may be damage to surrounding properties where flying debris may cause injury to spectators.

For many people when they think of demolition they will often have in mind the usage of explosives in the spectacular collapse of a tall building. This method is in fact called implosion using explosives. Implosion is vital for dense urban areas since it brings down a tall building so that the surrounding environment is damaged as little as possible. The collapse takes only a few moments for the building to crash into its own footprint.

Because of the dangers of dealing with explosives they are only used when other methods are too costly or impractical. Where there is a partial collapse of a building and there are still primed explosives that did not go off, workers will be in great danger since the remaining structure is very unstable. On the other hand the demolition has to carry on and secure the safety of the site.

Health and Safety

The work of demolition is an infinitely more technical and complicated process than most people would appreciate. The job is very dangerous and requires experienced and skilled operators to handle the job. It is essential that personnel working in the market are appropriately trained. Health and safety awareness is crucial in demolition services so a good idea is for operatives to have gained a certificate of Competence in Demolition to guarantee safety for both workers and public alike. All demolition jobs are regulated by way of the Construction, Design and Management Regulations.

These are some of the elements that go into the demolition process that an expert demolition company will have the expertise to put into place and gain the required planning approval.

Sequence of Demolition

An incorrect sequence of dismantling can lead to accidental collapse of the building because the stability of any structure is reliant on the interdependence of the component parts. Think of a house of cards and what happens if one of the supporting cards is taken away.

There is a strict sequence of events before any demolition can take place. Councils all over the country will have their particular specific list for planning approval within their area, but a typical order would be as follows:-

• Provision of data
Information has to be provided about the construction of the structure to be demolished. Details of its previous use and the appropriate demolition methods to be used, including disposal of hazardous substances, need to be submitted by the demolition company.

• Survey of Demolition
A thorough survey of the site to spot any structural problems, in addition to risks associated with hazardous or flammable substances, should be discussed in detail with the authorities. (E.g. A disused garage where petrol was stored is a potential fire hazard so preventative measures will likely need to be taken).

• Preferred and Safe Method of Work
A good demolition company should be able to select the correct method of disposal showing the outline dismantling process. Planning is essential for assiduous monitoring. The authorities will need an in depth statement of the safety procedures to used, and all parties involved need to agree the techniques before any demolition can take place.

• Preparation and Planning
Issues such as asbestos abatement, rodent baiting, dealing with hazardous substances, disconnecting utilities, and making safe any electric, gas or other services must be shown in the planning stage. There is a great deal of preparation to be done before even starting work on demolishing the property itself.

• Protection of the Public
Safety cannot be compromised so wherever you can find heavily populated areas around the demolition site the protection of the public is paramount. Any health hazards will need to be assessed and temporary services arranged, and people affected will need to be informed.

Conclusion

The aim in demolition is always to eliminate an unwanted structure as safely and quickly as possible and in our modern environment efforts are made to recycle or re-use most of the old material. This may not be a brand new idea even though the word itself is relatively modern. On the borders between England and Scotland after the Romans left, a substantial part of Hadrian’s Wall was hauled away and use was made of the beautifully dressed stone to construct the new buildings in the towns and villages nearby and several are still standing today.

Demolition work by its nature is a very risky business and demolishing any building is a complex and skilled process. The next time you observe demolition work occurring on a building give a thought to the people who work in a dangerous situation daily and how much is involved in the meticulous planning, regulations compliance, care and skill that goes on to carrying out the project to clear the path for our future.

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