Scaffolding in New Zealand - Best Practice Guideline for
SECTION 3: GENERIC SCAFFOLDING REQUIREMENTS
3.1 Tools of the trade
The tools and equipment commonly used to erect, maintain and dismantle scaffolding are described in this section.
- Scaffold spanner: "Scaffold spanners" or "scaffold keys" are the preferred tool for tightening and releasing nuts on scaffold fittings or couplers.
- Swing over spanner: A standard scaffolding spanner with a head to fit 7/16" or ½" nuts with the head attached to the handle with a pin or ball and socket assembly. The handle is between 200mm and 250mm long.
- Ratchet spanner: A scaffold spanner similar to a standard socket set ratchet with the head to fit 7/16" or ½" nuts. The socket is either made as part of the ratchet or is secured to the ratchet. The handle is between 200mm and 250mm long.
- Podger hammer: The standard podger hammer is made of mild steel and has a straight handle between 200mm and 250mm with a tapering podger end of the handle between 30 and 45 degrees to the handle. Podger hammers are the preferred tool for general hammering, tapping in wedges on system scaffolding, locking and releasing the cups on cuplock scaffolding, twisting and tightening the wire on wire ties, etc. Podger hammers can be used for locating or aligning holes on steelwork.
- Adjustable wrenches (crescent or shifter): An adjustable wrench, crescent or shifter is normally used where an obstruction prevents the use of a scaffold spanner. A spanner fits over the nut; an adjustable wrench slides around a nut. The use of an adjustable wrench should be kept to a minimum as it has a tendency to round off the nuts. The arm of an adjustable wrench should be between 200mm and 250mm long.
- Spirit level: A spirit level is usually no longer than 300mm long with level bubbles showing vertical, horizontal and sometimes 45 degrees. They can be magnetic to assist in holding to metal tube during levelling. Spirit levels are used to check that scaffolding members are horizontal, vertical or at 45 degrees.
- Tape measures or rules: A standard retractable tape measure or fold out rule is a useful tool for measuring distance off walls, bay lengths, lift heights, etc.
- Industrial wire nips or cutters: A flat ended set of wire cutters also used to grab, twist and tension wire. These are useful for cutting lashing for planks and cutting and tensioning "steelies" wire for screening.
- Scaffold belts: A scaffold belt is used to carry scaffold tools safely and securely but still allow easy access to the tools. The belt should be made of sturdy leather, canvas webbing or similar. Leather, canvas or wire frogs should be used to secure scaffold spanners, podger hammers, adjustable wrenches and nips. Rules, tape measures, and spirit levels should be secured in pouches to prevent displacement (see figure 9).
Figure 9: Typical scaffolder’s belt
3.1.1 Inspection of used equipment
Used scaffolding equipment should be inspected to identify items that are unsuitable or that fail to comply with relevant standards. Use the supplier's or manufacturer's guidelines to determine the suitability of scaffolding equipment for further use.
Used scaffolding equipment should be checked and graded in the following scale:
- Checked and is suitable for normal operations.
- Repaired e.g. replacing bolts on couplers or replacing wedges on modular scaffolding.
- Reduce length or cut down e.g. shortening of tubes, planks cut down.
- Downgrading e.g. downgrading a scaffold plank to a soleboard.
- Scrapped - taken out of service and disposed of to prevent reintroducing sub-standard equipment back into service.
3.1.1.1 What to look for when equipment is defective
| Item | Flaw or defect |
|---|---|
| Scaffold tube | Outside diameter less than 47.5mmSteel wall thickness for galvanised steel less than 2.9mmAluminium wall thickness less than 4.2mmEnds cut not square to the axisEnds flame cutUnduly pittedHeavily corrodedDistorted, twisted, bent or split |
| Couplers | No manufacturer's or supplier's markDistorted, stretched or crackedBent or stretched rivets or pinsThreaded blind holesStripped threads on bolts or nutsSeized bolts or nuts |
| Baseplates | Bent or distorted to prevent an even bearingThickness less than 6mmSurface area less than 225 square cm (less than 150mm x 150mm)Spigot less than 50mm long |
| Adjustable leg/ baseplate/castor | Extension exceeds 600mmMissing fixed stop enabling less than 150mm length of spigot to remain in the standardClearance between the inside diameter of the tube and the outside diameter of the spigot of more than 5mmSpigot distorted causing it to jam in the tubeSeized nutsThread damaged |
| Castors | No manufacturer's or supplier's markSafe working load or working load limit not markedFitted with pneumatic tyresWheel diameter less than 125mmPintle length (spigot) either internal or external less than 150mmDiametrical clearance between the pintle (spigot) and the standard more than 5mmWheel brake ineffective or missingNo means to positively fix castor to the standard. |
| Prefabricated structural components | Ends flame cutButt welded within its lengthUnduly pittedHeavily corrodedDistorted, twisted, bent or splitWelds cracked, broken or missingLocking devices damaged, inoperative, unrestrained or missing |
| Timber planks | Width less than 225mmNominal thickness reduced by 10%Laminations in laminated planks are separatingWarped, twisted, broken, split or wornEnd fixings missing or damagedPainted or treated in any way that may hide defectsDeep burnsOil stains or slippery surfaceNails projectingRot of any kindSaw cuts |
| Metal scaffold planks | Width less than 225mmDistorted, twisted, bent, split or crushedHeavily corrodedWelds cracked, broken or missingRivet broken or missingEnd pieces crushed or missing |
| Steel wire ropes | Safe Working Limit not markedFor suspended scaffolding hoists, any visible broken wiresFor hung scaffolds, more than 10% of the visible wires broken in a length equal to eight rope diametersOne or more broken wires immediately below a metalled socketOuter wires worn more than 33% of the nominal diameterBird caging or bird nestingCore poppedWire rope grips or bull dog clips have been used on the ropeThimbles distortedEvidence of corrosion |
| Chains | Safe Working Limit not markedLinks deformed, chipped, nicked, cracked or stretchedNominal diameter or dimension reduced by more than 10%Evidence of corrosion |
| Shackles | Safe Working Limit not markedCrown or pin diameter reduced by more than 10%Bolt used in place of a shackle pinDistortion or overstraining evidentEvidence of corrosion |
3.2 Common scaffolding bends and hitches
Rolling hitch: The recommended hitch used to raise and lower tube when used in conjunction with a half hitch.
Clove hitch: The clove hitch has been superseded by the rolling hitch as the recommended hitch for raising and lowering tube. If used it should be used in conjunction with a half hitch.
Sheet bend: A simple method of securing two different sizes of ropes together.
Buntline hitch: Secure method of securing a rope to a ring or tube.
Timber or plank hitch: The recommended hitch used to raise and lower planks or timber. The ropes tail can be wrapped around the noose up to five or six times if required, depending on the thickness of the rope and in conjunction with a half hitch if required.
Single bowline: A very simple method of creating a temporary eye at the end of a rope.
Square lashing: Used to secure a ladder to a tube for example.
Figure 8 knot: A quick and convenient general purpose knot that is the basis of many other knots.
3.3 Foundations
The foundation of a scaffold needs to be adequate to carry and distribute the loads it will bear.
3.3.1 General information
The foundations of a scaffold must be adequate to carry and distribute the loads imposed at each standard and over the whole loaded scaffold. On hard level surfaces such as steel or concrete standards should be supported on baseplates, however soleboards may not be necessary if the surface does not require protection. When using soleboards, the ground conditions under the proposed scaffold should be checked to determine the soleboard dimensions required to provide an adequate contact area to support the total load transferred down the scaffold standards.
Common types of ground conditions include: concrete floor slabs, tarseal or bitumen drives / car parks, compacted fill, uneven ground / rough terrain, sloping foundations, soft soils / sand. Particular attention must be paid to:
- Scaffolds erected adjacent to trenches and on slopes. Pressure exerted by the scaffold foundation may lead to subsidence.
- Areas prone to run-off or flooding. Water movement or saturation may cause subsidence or undermining.
To determine the size of the soleboard required to support a standard, information on the bearing capacity of the ground and the total design load of the standard is required. The bearing capacity of the supporting surface may be determined using table 7 as a guide.
| Ground Conditions | Nominal Bearing Capacity (kg/m2) |
|---|---|
| Soft clay - moulded by light finger pressure | 2000 |
| Sand | 5000 |
| Stiff Clay - Moulded by strong finger pressure | 7500 |
| Hard Clay - difficult to indent with thumb | 10,000 |
| Rock | 50,000 |
If you are unsure of the ground bearing capacity, check with a chartered engineer or have the ground tested to give a pressure bearing capacity.
Two factors determine the total design load of the standard:
- The dead load of the scaffold. This includes the weight of the standard and all attached components including ledgers, transoms, putlogs, braces, ties, planks, guardrails, and attachments such as sheeting. The weight of common scaffolding components is given in table 1 (section 1.2.2.6).
- The live load on any one standard based on the worst possible loading configuration i.e. full duty loading in adjacent bays. The single standard live load is calculated as 2/3 of the scaffold duty loading.
3.3.2 Foundations on sloping ground
Figure 10: Use of sloping ledger on sloping ground
Alternatively the standards can be held in place by using a sloping brace connected directly to the standards with swivel couplers.
Figure 11: Foundations on sloping ground - how not to do it.
A. Standards not centred on the baseplate or soleboard
B. Soleboard not fully bedded
C. Standard not evenly bearing on baseplate, soleboard and baseplate not horizontal
3.3.3 Soleboards
Scaffolding foundations must be adequate to carry the combined weight of the scaffold, including the imposed loads. Soleboards, also known as baseboards or soleplates, need to be used under most standards in conjunction with baseplates or basejacks. Timber soleboards must not be less than 200mm wide x 500mm long x 38mm deep. The soleboards are used to distribute the load of the standard over a larger ground area than just baseplates or basejacks.
Soleboards must sit flat under the standard. This may necessitate digging into the ground or packing up the ground to give a horizontal bearing surface for the soleboard. Figure 12 shows some different combinations of soleboards and how they can be used to help distribute the point loading on standards.
Figure 12: Use of soleboards in different combinations
The formula to determine the ground contact area for the soleboard is:
Vertical Load ÷ Bearing Capacity + Minimum Contact Area
For example, assume the scaffold is being erected on a stiff clay surface and each standard has a design load of 860kg. The calculation would be:
860kg ÷ 7500kg/m2 + 0.115m2
Using a timber scaffold plank 225mm wide as a soleboard means the approximate length for this example is 500mm (0.225 x 0.5m = 0.1125m2).
Soleboards should ideally be made from timber such as pinus radiata, hardwoods or laminated ply. Such materials as stacked timber 100mm x 50mm, concrete blocks, bricks or pallets must not be used. It is generally accepted that standard scaffold planks cut to size can be used for light duty scaffold only. Note that these cut planks tend to split along the laminations if placed upon uneven surfaces.
When the foundation is levelled concrete of adequate thickness or a similar hard surface such as steel, soleboards can be omitted, but baseplates, screwjacks or castors must always be used at the bottom of all standards.
3.3.4 Baseplates
Steel baseplates must be used under all standards that do not have a castor or basejack (screwjack).
Baseplates must be made from steel (usually mild steel) and be a minimum of 225 square centimetres x 6mm thick.
The baseplate must have a central spigot a minimum of 50mm long to centre the standard. The spigot must be sufficient to locate the standard (recommended 16mm).
Generally baseplates have 2 or 4 holes drilled into the baseplate to enable the baseplate to be secured to a soleboard by nails or similar.
Baseplates should always be accompanied by a soleboard unless the baseplate is placed directly on concrete of the correct depth (minimum 100mm) and strength to take the imposed loads, or directly onto steel.
3.3.5 Basejacks
Adjustable basejacks, also known as screwjacks or adjustable baseplates, are used under standards to provide a baseplate with the ability to be adjusted vertically.
The baseplate part of the basejack has the same minimum conditions as the baseplate. The spigot or stem of the basejack which is fixed to the baseplate must not have more than 600mm threaded extension and must have a minimum of 150mm length of spigot or stem to be inserted in the standard. Longer extensions can be used, but these must be to manufacturer's specifications or be designed by a chartered engineer.
It is recommended that the threaded extension, while maintaining a minimum 150mm-spigot or stem in or over the standard, should have a maximum extension that does not exceed half of the total extension. For example a castor with 500mm extension should preferably be kept to a maximum of 250mm extension but can be used out to 350mm extension. The threaded spigot or stem has a threaded section with a positioning nut. The nut generally has a small handle on two or more sides of the nut to assist in turning the nut for adjustment. The spigot or stem must have no more than 5mm clearance between the inside diameter of the standard and the top of the spigot or stem. This is why spacer nuts are placed on the top of the spigot or stem when standard basejacks are used in 60mm outside diameter tubes like shoreload frames. This spacer nut keeps the spigot or stem concentric in the wider diameter standard.
Basejacks can be used in conjunction with a U-head plate to act as a Uhead jack.
Basejacks can also be used horizontally to place a scaffold in compression, as when they are used in conjunction with a tube in a window frame to form a reveal tie. Traditionally basejacks are more commonly used in proprietary system type scaffolds.