Scaffolding, also called scaffold or staging, is a temporary structure used to support a work crew and materials to aid in the construction, maintenance and repair of buildings, bridges and all other man-made structures.
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There are five main types of scaffolding
There are five main types of scaffolding used worldwide today. These are tube and coupler (fitting) components, prefabricated modular system scaffold components, H-frame / façade modular system scaffolds, timber scaffolds and bamboo scaffolds (particularly in China and India). Each type is made from several components which often include:
- A base jack or plate which is a load-bearing base for the scaffold.
- The standard, the upright component with connector joins.
- The ledger, a horizontal brace.
- The transom, a horizontal cross-section load-bearing component which holds the batten, board, or decking unit.
- Brace diagonal and/or cross section bracing component.
- Batten or board decking component used to make the working platform.
- Coupler, a fitting used to join components together.
- Scaffold tie, used to tie in the scaffold to structures.
- Brackets, used to extend the width of working platforms.
Specialized components used to aid in their use as a temporary structure often include heavy duty load bearing transoms, ladders or stairway units for the ingress and egress of the scaffold, beams ladder/unit types used to span obstacles and rubbish chutes used to remove unwanted materials from the scaffold or construction project.
Foundations
Good foundations are essential. Often scaffold frameworks will require more than simple base plates to safely carry and spread the load. Scaffolding can be used without base plates on concrete or similar hard surfaces, although base plates are always recommended. For surfaces like pavements or tarmac base plates are necessary. For softer or more doubtful surfaces sole boards must be used, beneath a single standard a sole board should be at least 1,000 square centimetres (160 in2) with no dimension less than 220 millimetres (8.7 in), the thickness must be at least 35 millimetres (1.4 in). For heavier duty scaffold much more substantial baulks set in concrete can be required. On uneven ground steps must be cut for the base plates, a minimum step size of around 450 millimetres (18 in) is recommended. A working platform requires certain other elements to be safe. They must be close-boarded, have double guard rails and toe and stop boards. Safe and secure access must also be provided.
Basic scaffolding
The key elements of the scaffolding are the standard, ledger and transoms. The standards, also called uprights, are the vertical tubes that transfer the entire weight of the structure to the ground where they rest on a square base plate to spread the load. The base plate has a shank in its centre to hold the tube and is sometimes pinned to a sole board. Ledgers are horizontal tubes which connect between the standards. Transoms rest upon the ledgers at right angles. Main transoms are placed next to the standards, they hold the standards in place and provide support for boards; intermediate transoms are those placed between the main transoms to provide extra support for boards. In Canada this style is referred to as “English”. “American” has the transoms attached to the standards and is used less but has certain advantages in some situations.
As well as the tubes at right angles there are cross braces to increase rigidity, these are placed diagonally from ledger to ledger, next to the standards to which they are fitted. If the braces are fitted to the ledgers they are called ledger braces. To limit sway a facade brace is fitted to the face of the scaffold every 30 metres or so at an angle of 35°-55° running right from the base to the top of the scaffold and fixed at every level.
Materials
The basic components of scaffolding are tubes, couplers and boards.
The basic lightweight tube scaffolding that became the standard and revolutionised scaffolding, becoming the baseline for decades, was invented and marketed in the mid-1950s. With one basic 24 pound unit a scaffold of various sizes and heights could be assembled easily by a couple of labourers without the nuts or bolts previously needed
Tubes are usually made either of steel or aluminium; although there is composite scaffolding which uses filament-wound tubes of glass fibre in a nylon or polyester matrix, because of the high cost of composite tube, it is usually only used when there is a risk from overhead electric cables that cannot be isolated. If steel, they are either ‘black’ or galvanised. The tubes come in a variety of lengths and a standard outside diameter of 48.3 mm. (1.5 NPS pipe). The chief difference between the two types of metal tubes is the lower weight of aluminium tubes (1.7 kg/m as opposed to 4.4 kg/m). However they are more flexible and have a lower resistance to stress. Tubes are generally bought in 6.3 m lengths and can then be cut down to certain typical sizes. Most large companies will brand their tubes with their name and address in order to deter theft.
