Building Demolition

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10 March 2013
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Building Demolition

Building demolition is achieved by a variety of means and methods, using many kinds of equipment and tools. Demolition experts can recommend which methods are appropriate for particular projects. For simplicity, demolition methods can be grouped under the cate- gories of mechanical, implosion, and special.

Mechanical demolition.

demolition-in-actionThe most widely used method of building demolition today involves the use of various specialized mechanized equipment and tools. While the crane and wrecking ball have long been the symbol of large, high-rise demolition projects, demolition contractors employ a variety of high-reach excavators equipped with tools for crushing concrete and shearing steel at heights up to 120 feet. These machines can operate in confined work areas and can separate the building materials as they “chew” the building apart. Excavators equipped with special attachments, including hydraulic breakers, shears, and concrete processors, are also the machine of choice for demolishing foundations and handling debris and scrap metals. Interior demolition and selective demolition are most often accomplished with small, skid-steer loaders and small excavators equipped with a variety of hydraulic attachments that include breakers for concrete, shears for cutting small steel, and material-handling buckets and forks. In the last twenty years, effective remote-controlled machines have been developed that can be used in hazardous environments, confined spaces, areas that have been damaged or are structurally weakened, and areas that are sensitive to noise or vibration. These machines are also being used for selective demolition in radioactive environments.

Implosion

Implosion methods are very effective for bringing down high structures that would be difficult to reach with equipment or too expensive to demolish one floor at a time. These methods use highly specialized explosives to undermine the supports of a structure so it collapses either within its own footprint or in a predetermined path. The

implosion process is especially suited for high-rise buildings (usually more than twelve stories) and a variety of special structures (e.g., cooling towers, nuclear reactor contain- ments, space launch towers, smokestacks, boilers, steel mill furnaces, and so on). Common explosives—usually various forms of dynamite and ammonium nitrate—are fre- quently used to blast heavy concrete such as that in bridge piers and machinery founda- tions. Only a handful of companies are qualified in this demolition method, and they almost always work as a subcontractor to a conventional demolition contractor.

Special demolition

Certain types of demolition require specialized handheld tools for cutting, chipping, drilling, and breaking small amounts of materials (e.g., removing concrete for a new door in an active hospital, cutting and removing a specified pipe in a rack containing piping that is in use, removing a terra-cotta arch for reinstalla- tion, etc.). The tools for these tasks are mostly powered by hydraulic or pneumatic sys- tems and can usually be moved by two men.

Special demolition projects are various.

A typical project might require the con- tractor to remove partitions and suspended ceilings in a building area that is partially occupied, or cut new openings in concrete walls and floors for mechanical chases and doorways. Another special demolition type is careful removal of significant historic fabric in existing buildings. Often this is required when building systems are upgraded but the historic fabric (e.g., terra-cotta, windows, carved moldings, etc.) must appear to have been undisturbed afterwards. This process requires documentation prior to demolition and proper removal, cataloging, and storage of the historic building fabric.

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