Checking using BS 5975
There is often confusion surrounding the different categories of check that should be performed on a scaffold design. BS 5975:2008 is the only current British Standard that covers scaffolding and defines the requirements of each checking category.
Before looking at the design checks in detail it should first be noted that BS 5975:2008 gives recommendations and guidance on the procedural controls to be applied to all aspects of temporary works. This includes scaffolding!
The design check should be carried out before commencement of the construction work and should include checks on concept, adequacy, correctness and compliance with the requirements of the design brief. This means that every temporary works design should be preceded by a design brief. The items to be considered in the design brief are covered in section 8 of BS 5975:2008.
For clarification, the following information is taken from Table 1, BS 5975:2008, the 'scaffolding context' is the interpretation of 48.3.
Design Check: Category 0
Scope: Restricted to standard solutions only, to ensure the site conditions do not conflict with the scope or limitations of the chosen standard solution. Comment: This applies to the use of standard solutions and NOT the original design, which will require both structural calculation and checking to category 1,2 or 3, as appropriate. Independence of Checker: Because this is a site issue, the check may be carried out by another member of the site or design team. Scaffolding Context: This would be anything that constitutes a 'Basic Scaffold' as defined in TG20:08 which can be erected within the parameters of TG20:08 guidelines (or a system scaffold that conforms to the requirements of a standard solution in the User Guide for that system). As standard solutions, these scaffolds do not normally require a design, although one may be required by the main contractor or the client.
Design Check: Category 1
Scope: For simple designs. These may include: formwork, falsework (where top restraint is not assumed) needling and propping to brickwork in openings in single storey construction. Comment: Such designs would be undertaken using simple methods of analysis and be in accordance with the relevant standards, suppliers technical literature or other reference publications. Independence of the Checker: The check may be carried out by another member of the design team. Scaffolding Context: A few examples that would fall into this category would be simple bridges with beams, simple loading bays founded on the ground (such as typical brickwork for new build), straightforward towers and birdcages, Class A or B protection fans or edge protection made from scaffold components. Anything involving public protection or supporting the public, temporary roofs or buildings would NOT fall into this category.
Design Check: Category 2
Scope: On more complex or involved designs. Designs for excavations, for foundations, for structural steelwork connections, for reinforced concrete. Comment: Category 2 checks would include designs where a considerable degree of interpretation of loads or soils' information is required before the design of the foundation or excavation support or slope. Independence of the Checker: The check should be carried out by an individual not involved in the design and not consulted by the designer. This can be someone from the same organisation or from a different organisation. Scaffolding Context: Public protection, temporary roofs or buildings will either be category 2 or 3 depending on their complexity and the risks involved. Complicated bridging arrangements, heavily loaded birdcages, truss-outs, Line crossings, masts or scaffolds for vehicular access could all fall into this category. Network Rail, LUL and Highways Agency scaffolds will generally be either category 2 or 3 due to the increased risk (and consequences of failure) associate with interaction with the public or live vehicle movement. This means that even simple scaffolds normally checked as Category 1 or 2 may have to be checked as Category 2 or 3, due to their location or interaction with other works.
Design Check: Category 3
Scope: For complex or innovative designs, which result in complex sequences of moving and/or construction of either the temporary or permanent works. Comment: These designs include unusual designs or where significant departures from the standards, novel methods of analysis, or considerable exercise of engineering judgement are involved. Independence of the Checker: The check should be carried out by another organisation. Scaffolding Context: Network Rail and LUL related designs that are in close proximity to the running rail are usually checked as category 3. This category can also include shoring work, scaffolding used for structural support and any design providing or forming an access route for the public. The definition of a 'complex' or 'innovative' scaffold can be somewhat subjective but any significant variation from 'typical' scaffold arrangements can be considered complex. Such variations include unusual load paths (wind transferred through guy wires or beams on-flat) or bridging/cantilever beams at several levels in different directions. It is not possible to compile an exhaustive list of examples, or a set of rules, as the important determining factor is often the experience of those involved (designer, checker, TWC, contractor) and their familiarity or otherwise with the principles of the proposal.
For categories 2 and 3 the checker should carry out the check without reference to the designer's calculations using only the design brief, design statement, drawings, and specification and associated information not produced by the designer. In certain situations it may be possible to apply different categories of check to different parts of the design. For example, a largely typical scaffold with one elevation adjacent to a railway track may be checked as category 1, and the elevation adjacent to the track checked as category 3.
Clause 9.2.5 states that a design check certificate should be produced for all check categories, confirming that the design complies with the requirements of the design brief, the standards/technical literature used and the constraints or loading conditions imposed.
Most main contractors stipulate that temporary works should be designed in accordance with BS 5975:2008 however the design check is something that is often overlooked.