Scaffolding in New Zealand - Best Practice Guideline for
SECTION 6: PARTICULAR SCAFFOLDS AND SCAFFOLDING STRUCTURES - Continued
6.11 Mast-climbing work platforms
Mast-climbing work platforms are available for use as either freestanding units or in single or multiple tower configurations. Mast climbers are progressively tied to the building or supporting structure as they are erected.
When working with mast climbers:
- Always check manufacturer's specifications and instructions.
- If in doubt get a chartered engineer to check anchor points or the means of tying the mast-climber to the supporting structure.
- Check that the safe working load is clearly marked.
- Check the foundation can sustain the intended loads.
- Check that the base of the mast-climber has adequate protection.
- Ensure the mast is erected vertically and all approved ties are in place.
- Include testing requirements, pre-operational checks and servicing requirements.
Figure 84: Mast climbing work platform
6.12 Barrow ramps
Barrow ramps are a particular type of sloping platform. They contain cleats alongside an uncleated board or channel. This allows wheelbarrows or wheeled loads to be moved easily while guarding against slipping.
Figure 85 shows a typical barrow ramp erected using tube and fitting scaffold. Note the uncleated middle plank for the wheel of the wheelbarrow to run up and down.
Figure 85: Barrow ramp
For heavy loads such as wheelchairs or concrete laden wheelbarrows gradients of about 1:12 are appropriate. The maximum recommended slope for a cleated barrow ramp is 20 or 1 in 3.
6.13 Falsework or propping
Falsework or propping is used primarily to support a load. It is any temporary structure used to support a permanent structure while it [the permanent structure] is not self supporting.
6.13.1 Types of load
Dead Loads (self weight): The actual weights of the falsework structure, permanent materials (precast, concrete) and stored items (plant).
Live Loads (construction activity): The weight of personnel, impact e.g. heaping of concrete, and tools (small plant).
Environmental Loads (wind, earthquakes etc): Load added by environmental factors such as weather, earthquakes, etc.
Calculating total loading
When calculating floor loads for falsework the general loading used for live loads is 2kN/m (205kg/m). This is added to the combined dead load to give total loading and covers most applications outside the most severe weather conditions.
6.13.2 Units and loadings
| Physical Properties | Unit | Symbol |
|---|---|---|
| Length | Metre | m |
| Mass | Kilogram | kg |
| Area | Square metres | m |
| Volume | Cubic metres | m |
| Density | Kilograms per cubic metre | kg/m |
The mass of a 1 metric tonne (1,000kg) exerts a force of approximately 9.81kN (kilo Newton). Therefore:
1kg exerts a force of approx 9.81N (Newton)
100kg exerts a force of approx .981kN
To covert kg to N: #kg multiplied by 9.81
To convert N to kg: #N multiplied by 0.102
| General loading | |
|---|---|
| Sand dry/wet | 1680 kg per m/ 1920 kg/m |
| Timber pinus/m | 400 - 480 kg |
| Water per litre | 1.0 kg |
| Concrete wheel barrow approx 0.05m | 136 kg |
| Blocks concrete (400 x 200 x 200) | 19 kg per block |
| Worker average | 100.0 kg |
| Mass of concrete | kg/m |
| Average | 2300 |
| Heavy | 3200 |
| Average with 3% steel | 2550 |
6.13.3 Falsework design
When designing falsework establish:
- The structure to be supported.
- A proposed method(s) of falsework.
- By design, the integrity of the falsework to safely support all loadings associated with the work.
In determining what information to consult and how to approach falsework design, no single document provides all the answers. Sources of information for scaffolders, chartered and design engineers include:
- The manufacturer/designer loadings and proven test information (proprietary systems).
- Grade, quality and test results of scaffolding equipment (tube, clip, fittings).
- BS 5975:1996 Code of Practice for Falsework.
- AS/NZS 1170 parts 0 - 3 and NZS 1170.5
- Cement and Concrete Association of New Zealand Guidelines and documents.
- HERA (Heavy Engineering Research Association) publications on structural steel capacity, connections, loadings and use. Structural steel is used as, and/or in conjunction with, manufactured falsework equipment.
- HERA publication, Guide to practical aspects of composite floor system design and construction, including concrete placement. This includes information on controlling deflection of pumped concrete in composite floor systems.
- AS 3828 Guidelines for the Erection of Building Steelwork.
- AS 3610 Formwork for Concrete.
6.13.4 Standard falsework components.
Always follow the manufacturer's instructions and specifications, in particular the maximum safe working loads permitted.
Uhead jack and basejacks
- Maximum safe working load 53 kN (5405 kg) at 200mm extension.
- Maximum safe working load 41 kN (4180kg) at 450mm extension.
- Check manufacturer's specifications.
Adjustable props
Adjustable props consist of four parts:
- The outer tube (60mm OD) with welded baseplate.
- The inner tube (48.3mm OD) with welded top plate.
- The nut and handle.
- The prop pin.
Prop sizes range from 1050mm to 4900mm and can support a safe working load between 8kN (815 kg) and 42.5kN (4335kg) - 32kN (3265kg) on average. Refer to the manufacturer's specifications for safe working loads. Props must be adequately laced in one direction but preferably in two directions. It is recommended that lacing be positioned one third of the distance up the prop inner
Shoreload frames
Traditionally shoreload frames are 1220mm wide and range from 610mm high to 1830mm high. They are constructed from 60mm OD tube and give a safe working load of between 80kN (8160kg) and 100kN (10195kg) per frame. The shoreload frames are connected with frame braces of different lengths to form a tower. Frames can be stacked vertically on top of each other utilising frame joiners to give the desired height (see figure 86).
Figure 86: Typical shoreloading set up
Header beams
A number of beams may be used in falsework, including:
- Doka wooden beams.
- Rolled Steel Joist (RSJ).
- Laminated true form beams.
- Universal beams (UB).
- Aluminium A or I beams with a timber infill.
- Timber.
6.13.5 Concrete components
6.13.5.1 Precast
A concrete structure e.g. beam, panel, double T that is poured and set before being brought to the site. The precast can be pre-stressed in the case of shell beams and flat slabs. These traditionally only require propping to support the intended loads.
6.13.5.2 In situ
Concrete poured on site. This traditionally requires propping with primary and secondary beams to enable boxing to be formed to contain the concrete.
Basic propping can be used following the manufacturer's specifications. If there is any doubt concerning ground capacity, loadings etc you must get a chartered engineer to check the design and follow his/her recommendations. Falsework or propping should always maintain a factor of safety of 3 in all aspects of the design.
Traditional scaffolding (tube and fitting, kwikstage system, cuplock, rapid scaff and timber to name a few) can be used for propping. You must follow the manufacturer's specifications in all cases.
Please refer to the section on foundations. While propping is primarily to support a load, it also transfers it to the surface below - to the foundations. Thus, foundations are imperative when propping. In particular the ground capacity and seating of soleboards or bearers must be sufficient for the intended loads
Figure 87 shows how beams should be positioned in Uhead jacks (or similar) to keep the beam centred over the standard or support. The jacks must be rotated against the beam to centre the beam over the standard, prop or similar. The Uhead jack, prop, or similar must then be wedged or chocked to centralise the beam before being placed under load.
Figure 87: Positioning of Uhead jacks or similar
6.13.6 General falsework workmanship
The following are critical factors of falsework workmanship on site:
- The foundations should be satisfactory.
- The falsework should be constructed in accordance with the design, quality and quantity of components and the safe working loads as detailed in the manufacturer's specifications for components. This includes setting out.
- Tolerances should fall within allowable design limits.
- All connections should be properly constructed.
- Adequate access and egress must be assured.
Importance of detail
Constant emphasis is laid on the importance of careful attention to detail. Falsework usually consists of a comparatively large number of members to produce a supporting structure with multitude connections and junction conditions. The stability and integrity of the supporting structure should not be jeopardised by incorrect assembly of one of the many connections or junctions. Failure to get details right during the initial erection of the falsework could lead to local instability and may endanger the entire falsework structure.
Checking falsework
When dealing with falsework, check:
- The foundations before beginning erection.
- The proposed design of the intended falsework.
- Individual falsework components during the erection process.
- All connections and junctions during the erection process.
- Layout of falsework as per the design.
- All falsework for eccentricity of individual components.
- All falsework is positioned centrally under the intended loads.
- Falsework immediately before loads are applied.
- Falsework immediately after loads have been applied.
- Periodically after adverse weather conditions.
- Before dismantling that the structure is self-supporting.
Checking adjustable props
- Props should be undamaged and not visibly bent.
- Props should be plumb within 1.5 degrees of vertical (not exceeding 25mm out of vertical over a height of 1.0m).
- Props must be placed centrally under the member to be supported and over any member supporting the prop with no eccentricity exceeding 25mm.
- Props must be adequately laced in one direction but preferably in two directions.
- It is recommended that lacing be positioned one third of the distance up the prop inner.
6.14 Timber scaffolds
This section deals with standing scaffolds that comprise standards, ledgers, guardrails and putlogs made of timber.
Quality of timber and fittings
Radiata pine and Douglas fir are suitable timbers for use in timber scaffolding and must be either No 1 framing grade or standard building grade as specified in NZS 3631:1978 Classification and grading of New Zealand timber. Other types of timber may be used if they are of equivalent strength and quality.
All timber used in scaffolding should be preservative treated in accordance with an appropriate commodity specification of the Timber Preservation Authority. Commodity specification C7 is suitable for external scaffolding except when standards and sole plates are in direct contact with the ground in which case it is necessary to treat to commodity specification C3. For indoor scaffolding boron-treated timber is satisfactory. Untreated timber may be acceptable if the timber is sound and unlikely to deteriorate during the life of the scaffold.
Fittings used for connecting joints between standards ledgers and braces must be of adequate strength and be maintained in good condition.
Specific requirements
The design and construction of timber scaffolding for the support of both light-duty and heavy-duty working platforms must be carried out in accordance with sound engineering and trade practices and conform to appropriate New Zealand Standards. The requirements for single-standard (pole) light-duty scaffolds with putlogs cleated to wall or frame and for use up to 5m high are summarised below (see also figures 88 and 89):
Standards: 100mm x 50mm with a maximum spacing of 2.4m.
Putlogs: 150mm x 25mm or 100m x 50mm for a maximum span of 1.2m or 2/150mm x 25mm for a maximum span of 1.5m.
Bracing: Each standard must be tied to the wall by a putlog and braced longitudinally by a ledger and at least two diagonal braces for the length of the scaffold. An additional diagonal brace at 40 to 50 slope must also be provided for every 20m length of scaffold. The minimum size of the brace is to be 100mm x 50mm or 150mm x 25mm.
Guardrail and midrail: Minimum size 100mm x 50mm.
Kickboards: All timber scaffolds must have kickboards on all platforms
Platform width: A minimum of 675mm wide.
Figure 88: Single standard light-duty timber scaffold – general structure
Figure 89: Single standard light-duty timber scaffold - connection point detail
