The purpose of a working scaffold is to provide a safe place of work with safe access suitable for the work being done.
The basic components of scaffolding are tubes, couplers and boards.
The basic lightweight tube scaffolding that became the standard and revolutionized scaffolding, becoming the baseline for decades, was invented and marketed in the mid-1950s.
Tubes are usually made either of aluminium or steel. If steel, they are usually galvanised. The main difference between the two types of metal tubes is the lower weight of aluminium and their greater flexibility.
Boards provide a working surface for scaffold users. They are seasoned wood and the board ends are protected either by metal plates called hoop irons or sometimes nail plates. 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.
Couplers are the fittings which hold the tubes together. The most common are called scaffold couplers, and there are three basic types:
• Right angles couplers
• Putlog couplers
• Swivel couplers
Only right angle couplers and swivel couplers can be used to fix tube in a ‘load-bearing connection’.
To join tubes end-to-end, sleeve couplers are used.
The key elements of a scaffold are standards, ledgers and transoms. The standards, also called uprights, are the vertical tubes that 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. As well as the tubes at right angles there are ledger braces to increase rigidity, these are placed diagonally from ledger to ledger, next to the standards to which they are fitted.
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 lift height, ie the spacing between ledgers, is 2 m, although the base lift can be up to 2.7 m.
Scaffolds are only rarely independent structures. To provide stability for a scaffolding framework ties are generally fixed to the adjacent building/fabric/steelwork.
Independent Tied Scaffolds
An independent scaffold consists of a double row of standards, with each row parallel to the building. The inner row is set as close to the building as is practicable. The distance between the lines of standards should be the minimum necessary to accommodate the required number of boards and toe boards.
The standards should be connected with ledgers parallel to the building and fixed with right angle couplers. Transoms are then fixed to the ledgers with putlog couplers to support the recommended platform widths.
Sole boards and base plates should be used under each standard.
Ledger bracing is generally fixed to alternate pairs of standards and Sway bracing is required at intervals not exceeding 30m.
The scaffold should be tied into the building at the frequency recommended.
A putlog scaffold consists of a single row of standards, parallel to the face of the building and set as far away from it as is necessary to accommodate a platform of four or five boards wide, with the inner edge of the platform as close to the wall as is practicable.
The standards are connected by a ledger fixed with right angled couplers and the putlogs are fixed to the ledgers using putlog couplers.
In addition to the putlog couplers, there are also putlog tubes. These have a flattened end or have been fitted with a blade. This feature allows the end of the tube to be inserted into or rest upon the brickwork of the structure.The blade end of the putlog tube is normally placed horizontally on the brickwork being built, taking care to use the maximum bearing area.
Sole boards or base plates are usually fitted under each standard. The same number of ties applies as for an independent tied scaffold.
Sway bracing is required at intervals not exceeding 30m but, unlike independent tied scaffolds, ledger bracing is not required in the finished scaffold.
Access Birdcage Scaffolds
A birdcage scaffold consists of a mass of standards arranged at regular intervals in parallel lines, usually evenly spaced apart. These standards are laced together with a grid of ledgers and transoms at every lift height. The top lift is boarded to form the access platform for work on ceilings and soffits over an inside area.
The side bays of the birdcage may also be required to form a normal access scaffold to the walls supporting the soffit.
In the case of a birdcage scaffold covering a large plan area, the width of the edge bays may be reduced to three, four or five boards to meet the requirements for the particular type of access required round the edges.
Ledgers and transoms should be fixed to the standards with right angled couplers. In the top lift, transoms should be fixed to the ledgers with putlog couplers. Transoms to the working lifts in the side bays may be fixed to the ledgers to provide level support for the decking.
All birdcage scaffolds require to be braced and/or tied to ensure they are stable. The standards have to be adequately braced to be strong enough to carry the vertical loading. Birdcages should be stiff enough to resist lateral sway and horizontal loads and be safe from overturning. External birdcages should be braced to resist wind forces and anchored when necessary.
There must be no gaps in decking for the platform. Platforms should be no further than 150mm from the working edge, unless provided with guard rails and toe boards. Where scaffolds have more than 11 standards in line, it is not possible to rely on wall support only, because some standards will be too far from a support in at least one direction. Some bracing will be essential, but can be used in conjunction with tying and butting using intermediate parts of the structure.
The standards should be supplied with foot ties in at lease alternate bays in both directions to form boxes. Diagonal bracing of alternate boxes in two directions should be fixed. Ledgers or transoms should be joined with sleeve or parallel couplers.
Associated Scaffolding Towers
Free standing structures which are self-supporting and do not depend totally on other structures for their rigidity and stability.
Any ladder should be fixed to narrowest side of the tower, preferably inside the base area. It can be upright or angled.
Mobile Towers Only
Joints in standards should only be made with sleeve or parallel couplers.
Wheels or castors not less than 125 mm in diameter and fitted with brakes that cannot be released accidentally should be locked into the base of standards.
Mobile and Static Towers
Dimensions vary according to need, but standards should never be less than 1.2m or more than 2.7m apart.
Foot ties should be fixed approximately 150mm from the bottom of the standards.
Except for the working platform, ledgers and transoms should be fixed to the standards with right angled couplers.
Guard rails and toe boards will be necessary on all four sides, and the toe boards must rise at least 150mm above platform level. Guard rails must be at least 910 mm above the platform width with the distance between the top of the toe board and the guard rail not exceeding 470mm.