# Scaffold Design Calculations

### Why do we need scaffold design calculations?

• Design calculations are essential for all scaffold designs and, by extension, for ALL scaffolds.
• This includes bespoke designs, as well as 'generic' standard solutions, such as those provided by the NASC TG20:13 e-guide (which are backed up by analysis).
• The PURPOSE of scaffold design calculations (and therefore the REASON that they are required) is to substantiate the scaffold design drawings, i.e. to prove that they work! Without calculations a design is incomplete and cannot be used.
• If any doubt remained as to the importance of scaffold design calculations, it should be dispelled by the legal requirement for scaffold designs, which is specifically a requirement to provide calculations:

Additional requirements for scaffolding

7. Strength and stability calculations for scaffolding shall be carried out unless—

1   (a)  a note of the calculations, covering the structural arrangements contemplated, is available; or

2   (b)  it is assembled in conformity with a generally recognised standard configuration. "

(Working at Height Regulations 2005, Schedule 3 Part 2)

•    "Substantiate (verb) : to establish by proof or competent evidence"

(Merriam-Webster dictionary)

◦    Absolute mathematical proof is typically not feasible in either a practical or an economical sense, due to the nature of temporary works and engineering in general.

◦    'Competent evidence' is therefore the minimum standard required of any scaffold design calculations, in order to 'prove' the strength and stability of the designed scaffold structure.

## What do scaffold design calculations have to include?

Exact calculation methods and design approaches can vary, but the basic requirement of any scaffold design calculation must include all of the following:

1.   An assessment of the loading conditions and combinations on the structure (dead, live, wind, snow load etc.)

2.   A check of the capacities of ALL scaffold components to sustain the loads and combinations of loads imposed.

3.   An evaluation of the stability and the rigidity of the scaffold structures, ensuring that adequate factors of safety are maintained.

4.   Identification of loads imparted BY the scaffold into foundations / adjacent structures. This is not strictly necessary to prove the adequacy of the scaffold itself, but since the integrity of the scaffold is generally reliant upon safe transmittal of such loads, calculation of them is necessary to allow the responsible parties to perform the appropriate substantiation process for the supporting / adjacent structures.

## Design calculations by 48.3 Scaffold Design

• Our scaffold design calculations are clear, precise and accurate. They are completed in accordance with current British and European Codes of Practice including BS EN 12811-1 (often using the guidance in NASC TG20:13 when completing scaffold designs using tube & fittings), BS 5975:2008 and Eurocode 1. The design calculations are cross-referenced to the design drawings and design risk assessment so that they can be easily followed and interpreted.
• All design calculations are produced and presented electronically (hand / written calculations are also used but only as provisional calculations or secondary checks). Good presentation is important, particularly when designs are checked by a third party: with our design package, it is always clear that all critical components, load combinations and load paths have been checked, without ambiguity or discrepancy.
• Our clearly presented and rigorous design calculation package is always approved by clients and checkers, with practically zero requests for additional checks, information or re-analysis during the approval process.
• Where appropriate (for example temporary roof structures, as illustrated in the example project below) structural analysis software is used to assess the scaffold under applied load cases; this is either a 2D or 3D frame with characterised members, nodes and supports. Analysis software is never used in isolation – always as part of a wider calculation package.

A selection of the most common codes of practice we use to complete our designs are:

• BS 1139* Metal scaffolding
• BS 2482 Timber scaffold boards
• BS 5950-1:1990* Structural Steelwork
• BS 5973: 1993* Access and working scaffolds and special scaffold structures in steel
• BS 5974:1990 Temporarily installed suspended scaffolds and access equipment
• BS 5975: 2008 Code of practice for temporary works procedures and the permissible stress design of falsework
• BS 6399: Pt 2: 1997* Code of practice for wind loads
• BS 8118 Part 1: 1991* Structural Use of Aluminium - Code of Practice for Design
• BS EN 12810-1:2003 Façade scaffolds made of prefabricated components - products specifications
• BS EN 12811-1:2003 Temporary works equipment: Scaffolds - Performance requirements and general design
• BS EN 13374:2004 Temporary Edge Protection Systems - Product Specification, test methods
• BS EN 1991 Part 1-4:2005 Eurocode 1: Actions on structures - General Actions - Wind Actions
• BS EN 1991-2:2003 Eurocode 1: Actions on structures - Part 2: Traffic loads on bridges
• BS EN 39: 2001 Loose steel tubes for tube and coupler scaffolds - Technical delivery conditions

Codes of practice have been withdrawn, however still used for reference.

We have left the full Eurocode series off this list for ease (and space!)

A selection of the industry guides we use to complete our scaffold designs are:

• HSG 33: 1999 Health & Safety in Roof Work
• SG28:09 Safe System of Work for Scaffolding associated with Timber Frame Building Construction
• SG4:10 The use of Fall Arrest Equipment Whilst Erecting, Altering & Dismantling Scaffolding
• TG4:11 Anchoring systems for scaffolding
• TG20:08 NASC Technical Guidance on the use of BS EN 12811-1
• TGN(E) 190: 2004 Design and use of temporary scaffold guards

## Design Documents produced by 48.3

All the design documents produced by 48.3 Scaffold Design are customer branded and customer owned. Electronic documents are digitally encrypted for client security and password protected if required.

Scaffold design documents are typically supplied in controlled .pdf format to a client specified distribution list under 48.3 document control procedures. All colour prints are sent first class to a nominated person for internal distribution.

## Example Project - Tempsford Hall (Kier Headquarters), for Modus Access / Kier

•    Rolling (i.e. moveable) temporary roof on Layher Allround support & access scaffold.

•    Original concept drawings developed into working scaffold design with the aid of frame analysis as part of design calculation package.

•    Design package approved by Kier temporary works department without any requirement for additional or revised calculations.

•    Scaffold successfully installed on site, and awarded an extremely rare 'Blue Flag' from Kier, resulting in visits / inspections from senior kier staff to view the scaffold as an example of good practice.

See our portfolio entry for further details on this project.

Scaffold erection in progress with first four trusses of rolling temporary roof installed.

Frame analysis from design calculations: model structure, supports and load combinations.

Frame analysis from design calculations: model structure, supports and bending moments.

3D Scaffold model produced for Modus Access as part of their successful tender package.

Scaffold design drawing showing section of scaffold analysed in structural model pictured above.