Scaffolding in New Zealand - Best Practice Guideline for
SECTION 4: TUBE AND FITTING SCAFFOLDING
4.1 Introduction
Tube and fitting scaffolds are generally not covered by manufacturer's specifications, engineer's certificates or producer statements, hence the need to have general scaffolding requirements for them. These general scaffolding requirements must also be used when altering proprietary scaffolds with tube and fitting components when the manufacturer's specifications or engineer's requirement do not include these alterations.
Figure 13: Standard tube and fitting scaffold showing general scaffolding terminology
[Inside guardrails have been omitted for clarity.]
4.1.1 General descriptions
Bay length
The horizontal distance between standards running parallel to the work face or in the longitudinal plane of the scaffold. Maximum bay length permitted for non proprietary scaffolds is 2.4m.
Bay width
The horizontal distance between standards running perpendicular to the work face or on the transverse plane of the scaffold. Maximum bay width permitted for non proprietary scaffolds is 1.575m.
Scaffold lifts
The vertical distance between structural ledgers or work platforms.
For clearance purposes a base lift should have a maximum height of 3.0m to the first work platform or structural ledger. Working lifts are generally 1.8m to 2.1m apart. It is recommended that a base lift (or kicker lift) should be used within 1.0m of the supporting structure.
A dummy lift is a level of structural ledgers that does not have a work platform. For instance if a scaffold has working platforms at 2.1m and 6.1m, the 4.1m lift between them is not planked and is called a dummy lift. The Top Working Platform (TWP) is also known as the Top Lift.
Scaffold area
The horizontal length of a scaffold in metres times the average height of the scaffold will give the scaffold area in square metres. So:
Length (m) x Average Height (m) = Area (m2)
The height of the scaffold may be taken from of the height of the top-working platform or alternatively from the top guardrail.
Example
A scaffold is 10.0m high to the top working platform at one end and 5.0m high to the top working platform at the other end. The scaffold is 24.0m long (see figure 14).
Length: 24m
Average height: 10.0m + 5.0m = 15m ÷ 2 = 7.5m
Area of scaffold: 24m x 7.5m = 180 m2
Figure 14: Calculating the area of a scaffold
4.2 Tube and fitting scaffolding components
4.2.1 Tubes
These are the most basic scaffolding components. Table 8 sets out the dimensions and properties of scaffold tubes from relevant standards. Tube loadings are dealt with later.
| Dimension and properties | Steel tubes to BS 1139 or AS/NZS 1576.3 | Galvanised steel tube to BS 6323 | Aluminium tubes to BS 1139; or AS/NZS 1576.3 |
|---|---|---|---|
| Outside diameter (mm) | 48.3 (± 0.5 tolerance) | 48.3 (± 0.5 tolerance) | 48.3 (± 0.5 tolerance) |
| Thickness (mm)seamless | 4.0 (± 0.5 tolerance) | 3.2 (± 0.48 tolerance) | 4.47 (± 0.56 tolerance) |
| Thickness (mm)welded | 4.0 (± 0.8; g - 0.4 tolerance) | 3.2 (± 0.32 tolerance) | |
| Mass per linear metre | 4.37 kg/m | 3.56 kg/m | 1.67 kg/m |
| Minimum tensile strength | 340 MPa | 360 MPa | 295 MPa |
| Yield strength | 210 MPa | 215 MPa | 255 MPa |
| Radius of gyration | 15.7 mm | 16.0 mm | 15.6 mm |
| Cross-sectional area | 557 mm2 | 453 mm2 | 615 mm2 |
| Moment of inertia | 138,000 mm4 | 116,000 mm4 | 149,000 mm4 |
| Elastic modulus | 5700 mm3 | 4800 mm3 | 6180 mm3 |
4.2.2 Fittings (couplers)
Right angle coupler (R/A), 90 degree coupler or double coupler: The most commonly used load-bearing coupler. Used to connect tubes at right angles. They come in many different designs that have their own preferred use in connecting standards to ledgers. Made of cast, forged or pressed steel. Permissible load (slip along a tube): 6.2kN (630kg)
Swivel coupler: Coupler used to connect two tubes together at any angle. Made of cast, forged or pressed steel. Permissible load (slip along a tube): 6.2kN (630kg). Not classified as a load bearing coupler due to the centre pin.
Putlog coupler or single coupler (two types): Coupler used to connect two tubes at right angles (putlogs to ledgers). Made of cast, forged or pressed steel. Permissible load; (force to pull tube axially out of the coupler): 0.59kN (60kg). The axial load permitted on a putlog coupler is 1/10 of the axial load permitted on a double coupler.
Two standard types of putlog coupler are the blade, half hand or pigs ear and the double flap or butterfly. The double flap type is not to be used to connect a putlog to a ledger if inside planks are to be used. Double flaps or butterflies can be used to connect timber to scaffolds.
Sleeve or external joiner: Coupler used to connect two tubes end to end. Each side of the joiner must be individually tightened. The joiner must have an internal partition or stopper to centre the fitting.
Pin or internal joiner: Coupler used to connect two tubes end to end. Has a pin arrangement, which expands in the tube. Must use same thickness tube and same inside diameter (ID). Tube must be circular and regular with the same nominal bore (NB).
| Description of fitting | Type of loading | Safe working load |
|---|---|---|
| Right-angle couplers | Slip along tube | 6.25 kN (640 kg) |
| Swivel couplers | Slip along tube | 6.25 kN (640 kg) |
| Joint pins (expanding spigot couplers) | Shear strength | 21 kN (2140 kg) |
| Sleeve couplers | Tension | 3.1 kN (315 kg) |
| Adjustable baseplate | Axial | 30 kN (3058 kg) |
4.2.3 Planks
Scaffolding platforms, erected to support workers and/or material are often made of planks. Refer to the following plank standards for quality criteria.
AS/NZS1576.1 Duty loads
AS/NZS 1576.3 Prefabricated platforms
AS 1577 Scaffold planks
AS/NZS 4357 Structural laminated veneer lumber (LVL planks)
AS/NZS 4576 Guidelines for scaffolding
In the absence of a NZ standard it is recommended that planks meet the requirements of AS 1577 or equivalent, with the exception of vertically laminated planks, which should have each laminate the full length of the plank.
Horizontally laminated planks should be manufactured to AS/NZS 4357 and must meet the performance criteria of AS 1577 or equivalent. All plank manufacturers should have a third party auditor to inspect their manufacturing and testing standards. All planks must bear the seal of an independent, nationally recognised third party inspection agency.
Planks in service should be tested in accordance with the manufacturer's specifications and/or the in service plank testing methods described below.
Width: Minimum 225mm wide
Depth: Minimum 38mm deep
Scaffold planks must be visually checked each time they are used on a scaffold. Look for:
- Twists or warping.
- Splits.
- Breaks.
- Wear and tear.
- Saw cuts.
- Notch cut out.
- Nails.
- Deep oil deposits.
- Build up of concrete and mortar.
- Deep burns.
- Rot.
4.2.3.1 General maintenance of planks
Planks should be fillet stacked after each use. This will allow the plank to dry before being stacked under cover ready for use. During the filleting a visual inspection and assessment of each plank can be made identifying any problems as listed above. Planks can be cut down to eliminate the affected areas.
In service plank testing
It is recommended that planks be tested annually through an approved testing machine. This is to ensure all practicable steps have been taken to see that the plank is suitable for its intended purpose. With the removal of NZS 3620 by Standards New Zealand annual testing of planks is recommended as the quality of planks may come into question.
There are three basic tests for planks in use:
- Simply supported impact test.
- Cantilevered impact test (refer AS/NZS 4576).
- Four point bending test as described below.
Four point bending test
A scaffold plank is placed over two rollers 2.4m apart. A UDL load of 2.2 kN (225kg) is applied over a cradle 300mm either side of the centre of the plank. The load should be applied for 1 to 3 seconds on either side of the plank.
The test is successful if the plank carries the load without signs of distress or permanent set. Please refer to the manufacturer's specifications/operating procedures to ensure compliance.
Thus, a scaffold plank should be capable of sustaining a total working load of 2.2 kN (225kg) applied to the full width of the plank at two equal loads 300mm on either side of the centre of the span when it is simply supported at 2.4m centres.
Figure 15: In service testing of scaffold planks for strength
Thus, a scaffold plank should be capable of sustaining a total working load of 2.2 kN (225kg) applied to the full width of the plank at two equal loads 300mm on either side of the centre of the span when it is simply supported at 2.4m centres.
4.3 Basing out tube and fitting scaffolds
4.3.1 Two pole return
Basing out a tube and fitting scaffold can lead to a variety of methods for the placement of standards in a corner or return. It is recommended that two standards are positioned at each corner or return. Figure 16 shows a light duty scaffold with both left and right returns and inside and outside corners. All are two pole returns with a minimum of two standards at each corner.
Rule of thumb: "If the scaffold turns to the right; two standards go on the left. If the scaffold turns to the left; two standards go on the right"
Figure 16: Basing out – two pole returns
4.3.2 Single pole return
Single pole (one standard) corners can be used if a set of standards in one direction are within 2.4m of the external single pole corner and within 1.575m in the other direction i.e. light duty (see figure 17).
Figure 17: Basing out – single pole returns
Longitudinal bracing (face bracing) must be used in both directions from as low as possible on the single pole return. The longitudinal bracing must run from the bottom of the single exterior standard angling up along each face of the scaffold.
This is to ensure that if the single pole is undermined or damaged the longitudinal bracing will support the corner of the scaffold and transfer the weight of the corner to the other sets of standards - one within 2.4m of the corner and one within 1.575m of the corner.
This method has the advantage of being able to dismantle one elevation or run of the scaffold and not having to add an additional standard to the scaffold. Generally on an external return the two inside standards are positioned approximately 300mm on either side of the building being scaffolded. If one elevation or run is dismantled, the two standards 300mm from the corner are used and only stop ends are required to complete the end of the scaffold. The end user of the scaffold can reach 300mm to the corner of the building.
4.3.3 Basing out over obstructions or trenches
Figure 18 shows how you can base out over an obstruction or trench by using longer soleboards to distribute the load on the standards closest to the trench and to spur up the standards closest to the trench. This will also transfer the load from these standards to standards not affected by the trench.
Figure 18: Basing out over a trench
4.4 Staggering of standards and ledgers
4.4.1 Staggering standards
On a tube and fitting scaffold, standards must be staggered if the top working platform is higher than the longest length of tube.
To stagger standards means to erect standards so that only one standard in a pair finishes in any one vertical lift. Ideally use one short standard on the inside with one long standard on the outside, then alternate that on the next set of standards - one long standard on the inside with one short standard on the outside (see figure 19).
Try to keep the standard joins as close as practical above the deck level. This will greatly assist the topping off or hemping of the next standard. Each set of standards should have a putlog within 300mm of the standards.
Figure 19: Staggering of standards and ledgers
4.4.2 Staggering ledgers
On a tube and fitting scaffold, stagger the ledgers so that, for example, one inside ledger finishes in a bay and the next ledger finishes in another bay (see figure 19).
Try to keep all ledger joins within 300mm of the standards. Guardrails should be staggered in the same way as standards and ledgers.