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Most construction scaffolding falls into one of three general categories: self-supporting, suspension, or special-use scaffolds. Self-supporting scaffolds consist of work platforms and the various structures that support them, with tube and coupler construction being the most common assembly method. Other self-supporting types include mobile, fabricated frame and pole scaffolds. Suspension scaffolds are suspended from above by ropes or other non-rigid methods, and include many job-specific variations. Similarly, special-use construction scaffolding takes many different forms dictated by the type and location of the work being performed.
Self-supporting scaffolds include those with fabricated welded tubular frameworks composed of end frames that have integral posts and horizontal bearers, plus intermediate members to support work platforms. Tube and coupler construction scaffolding is erected using couplings that join various members, including runners, braces, bearers, and uprights. Supported mobile scaffolds can be powered or nonpowered, are mounted on wheels or casters, and usually have a fabricated or tube and coupler frame. Single-pole scaffolds are supported on one side by a row of poles and other members, and on the other side by the building itself. The platforms on double-pole scaffolding are supported by a double row of uprights that are independent from the main supports.
Building codes and work safety rules in the U.S. generally require that suspension scaffolds and every component used in them be able to support at least four times their rated load weight. Ropes, cables, and other hardware used to adjust the scaffold's height must be able to withstand six times the load. Supporting hardware, such as cornice and roof hooks and parapet clamps, are made of high-strength steel or similar materials. Suspension construction scaffolding incorporates either a powered or manual hoist and brake that safely moves the work platform up and down. An automatic brake or locking pawl is designed to engage if the platform begins descending too rapidly.
Special-use construction scaffolding, as the name implies, is designed to deal with specific building conditions. Roof bracket scaffolds are supported from the rooftop using triangular supports and brackets that are appropriate for the roof's slope and construction, while outrigger scaffolds have platforms supported by outrigger beams that project beyond the building's wall while the inboard ends of the scaffold are secured to the building itself. Pump jack scaffolds have fixed vertical support poles with movable support brackets, whereas ladder jack and horse scaffolds are supported by ladders and horses, respectively. Aerial lifts are vehicle-mounted scaffolds with powered or non-powered platform lifting apparati, and include devices such as ladder and tower trucks as well as articulating and extensible boom platforms.
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