What is Scaffolding
Scaffolding Tubes are usually made either of steel or aluminium, although there is Composite material, 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 diameter of 48.3 mm. (1.5 Nominal Pipe Size|NPS). 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) and also their greater flexibility and so their lower resistance to force. 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.
Boards provide a working surface for scaffold users. They are seasoned wood and come in three thicknesses (38 mm (usual), 50 mm and 63 mm) are a standard width (225 mm) and are a maximum of 3.9 m long. The board ends are protected either by metal plates called hoop irons or sometimes nail plates, which often have the company name stamped into them. Timber scaffold boards in the UK should comply with the requirements of BS 2482. As well as timber, steel or aluminium decking is used, as well as laminate boards. In addition to the boards for the working platform, there are sole boards which are placed beneath the scaffolding if the surface is soft or otherwise suspect, although ordinary boards can also be used. Another solution, called a scaffpad, is made from a rubber base with a base plate moulded inside; these are desirable for use on uneven ground since they adapt, whereas sole boards may split and have to be replaced.
Couplers are the fittings which hold the tubes together. The most common are called scaffold couplers, and there are three basic types: ”right-angle couplers”, ”putlog couplers” and ”swivel couplers”. To join tubes end-to-end ”joint pins” (also called spigots) or ”sleeve couplers” are used. Only right angle couplers and swivel couplers can be used to fix tube in a ‘load-bearing connection’. Single couplers are not load-bearing couplers and have no design capacity.
Other common scaffolding components include base plates, ladders, ropes, anchor ties, reveal ties, gin wheels, sheeting, etc.
Most companies will adopt a specific colour to paint the scaffolding with, in order that quick visual identification can be made in case of theft. All components that are made from metal can be painted but items that are wooden should never be painted as this could hide defects.
Despite the metric measurements given, many scaffolders measure tubes and boards in imperial units, with tubes from 21 feet down and boards from 13 ft down.
Bamboo scaffolding is widely used in Hong Kong, with nylon straps tied into knots as couplers. Hong Kong Buildings Department, ”Guidelines on the Design and Construction of Bamboo Scaffolds”
The key elements of a scaffold are ”standards”, ”ledgers” and ”transoms”. The standards, also called uprights, are the vertical tubes that transfer the entire mass 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. Since scaffolding is a physical structure, it is possible to go in and come out of scaffolding.
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.
Of the couplers previously mentioned, right-angle couplers join ledgers or transoms to standards, putlog or single couplers join board bearing transoms to ledgers – Non-board bearing transoms should be fixed using a right-angle coupler. Swivel couplers are to connect tubes at any other angle. The actual joints are staggered to avoid occurring at the same level in neighbouring standards.
The spacings of the basic elements in the scaffold are fairly standard. For a general purpose scaffold the maximum bay length is 2.1 m, for heavier work the bay size is reduced to 2 or even 1.8 m while for inspection a bay width of up to 2.7 m is allowed.
The scaffolding width is determined by the width of the boards, the minimum width allowed is 600 mm but a more typical four-board scaffold would be 870 mm wide from standard to standard. More heavy-duty scaffolding can require 5, 6 or even up to 8 boards width. Often an ”inside board” is added to reduce the gap between the inner standard and the structure.
The lift height, the spacing between ledgers, is 2 m, although the base lift can be up to 2.7 m. The diagram above also shows a kicker lift, which is just 150 mm or so above the ground.
Transom spacing is determined by the thickness of the boards supported, 38 mm boards require a transom spacing of no more than 1.2 m while a 50 mm board can stand a transom spacing of 2.6 m and 63 mm boards can have a maximum span of 3.25 m. The minimum overhang for all boards is 50 mm and the maximum overhang is no more than 4x the thickness of the board.