3 Clause 2.2 states that: 'the reliability required for structures within the scope of EN1990 shall be achieved by:

• Design in accordance with EN1990-1999
• Appropriate execution
• Quality management procedures'.

4 Clause 2.5 (Quality Management) refers to 'organisational measures' and 'controls at the stages of design, execution, use and maintenance' being in place.

5 There is a note (following Clause 2.5) which indicates that EN ISO 9001: 2000 is an acceptable basis for quality control management, where relevant. Hence there is an assumption that a structured quality control system is required although not necessarily one which is formally registered.

6 Annex B to BS EN1990 (Management of structural reliability for construction works) provides greater explanation and is referenced in the commentary to assumption 3.

The six assumptions behind Clause 1.3

7.1 1-The choice of the structural system and the design of a structure is made by appropriately qualified and experienced personnel.

7.1.1 The choice of an appropriate structural system and the adequacy of the associated design are clearly very important. SCOSS has advocated project risk reviews [1] which would allow this assumption to be tested in the early days of a project. In so far as these choices might affect safety, the Construction (Design and Management) Regulations 2007 (CDM) also require consideration to be given to the structural system and design process. The considerations might include:

7.1.2 A record of such a review should be retained in the project files.

7.1.3 SCOSS is currently developing a guidance note relating to the independent review of certain structures [2]; this would greatly assist in compliance with assumption 1 in these cases.

7.1.4 The use of appropriately qualified and experienced personnel is commented on in 7.2 below.

7.2 2-Execution is carried out by personnel having the appropriate skill and experience.

NOTE: in this clause it is assumed that 'execution' is meant in the dictionary sense of 'performing a task', and hence it encompasses 'design' as well as 'construction'. Elsewhere in the Eurocodes it excludes design activity.

7.2.1 The need for personnel who have the appropriate skill and experience is a requirement which relates to both the design phase and the execution phase. Both phases are commented on in this section and fall within the ambit of the Construction (Design and Management) Regulations 2007 (CDM 2007).

7.2.2 These regulations require those involved in 'construction work' to be competent unless under supervision. The associated Approved Code of Practice (ACoP) [3] gives guidance in respect of the corporate competence of the organisations and of the individuals involved. It is important (and a specific requirement) that those who lack competence e.g. from a shortage of experience, are allocated appropriate supervision.

Design

7.2.3 In the early days of Eurocode application few design practitioners will have any experience in its use. Hence the supervision, checking and review processes will need to reflect this 'immaturity' to ensure that an appropriate level of confidence is attained. Although much of the Eurocodes is similar to existing codes of practice such as BS 8110 or BS 5950, there are some key differences which could lead to errors until fully assimilated into contemporary practice e.g.:

• in steel design the orientation of the x-x and y-y axes differ to current practice
• the Eurocodes adopt the continental style of ',' for a decimal point. Thus, 2.34 is given as 2,34, and spaces are introduced, e.g. 1 000 in lieu of ','
• new software that does not have the benefit of established use to have identified any bugs/misinterpretations.

7.2.4 Further examples of potential misunderstandings are given on the SCOSS website, on the Eurocode Expert website (www.eurocodes.co.uk) and in occasional 'Q&A' articles in The Structural Engineer.

7.2.5 Part of the project risk assessment (illustrated in paragraph 7.1.1) should be devoted to an assessment of the proposed design staff.

Contractors

7.2.6 Designers may need to alert the client to any specific requirements, relating to those who may construct the structure. These might relate to the complexity of the structure or fabrication needs. These can then be ensured during the pre-qualification and tendering process. Particular attention should be paid to ensuring the requisite standard is applied to all subsequent sub-contract arrangements.

7.3 3-Adequate supervision and quality control is provided during the execution of the work, i.e. in design offices, factories, plants, and on site.

NOTE: in this clause 'execution' is meant in the dictionary sense of 'performing a task', and hence it encompasses 'design'.

7.3.1 The requirement for adequate supervision and quality control is applicable to all stages of the project. It is clear from paragraph 5 that such supervision and quality control should be of a recognised standard, broadly consistent with one complying with ISO BS 9001.

7.3.2 Most sections of the Eurocode have references to other BS ENs which spell out the requisite quality standards relating to the construction stage e.g. BS EN 3834 (welding); BS EN 13670 (execution of concrete structures) and, until such time as the National Annex is available, the National Structural Concrete Specification (NSCS).

7.3.3 There are no specific cross references to the supervisory levels or quality control of designers. This links back to paragraph 7.2.3.

7.3.4 EN1990 allows for some variation in supervision and quality control, within the scope of a recognised quality management system, depending upon the classification of the structure (Annex B Table B4 and B5). These tables are repeated below.

7.3.5 The 'RC' classification in the tables refers to a structure's reliability; it relates to the consequences of failure, as noted below (see also Table 8.4 of ref 10):

7.3.6 Designs to the Eurocodes will normally be based around CC2/RC2

Table B4

7.37 Checking '… in accordance with the procedure of the organisation' is taken to mean in accordance with the design organisation's quality control system noted in paragraph 5. Annex 5 B4 clause (2) states that design supervision levels may be linked to these reliability classes or the importance of the structure, in accordance with National requirements or the design brief, and implemented through the quality management measures mentioned in paragraph 5.

7.38 Without supplementary clarification, this is considered to be too vague; it is suggested therefore that it will need careful clarification on a project by project basis and should feature also as part of the project risk review.

Table B5

7.39 Inspection 'in accordance with the procedures of the organisation' is taken to mean in accordance with a quality control system noted in paragraph 5. However this relates to the procedures of the 'executing' organisation i.e. the contractor, which may not match the expectations or requirements of the designer. Hence, this may require contractual clarification.

7.4 4-The construction materials and products are used as specified in EN 1990 and ENs 1991 to 1999 or in the relevant supporting material or product specifications.

7.4.1 This must be achieved through adequate contract documentation, coupled with appropriate supervision as noted in 2 above. SCOSS is aware, for example, that:

• changes are sometimes made on site to specified items [4], without the necessary involvement of the designer.
• some products are incompletely specified e.g. steel [5].

Such occurrences will invalidate this assumption.

7.4.2 The use of CE marked products, in accordance with the Construction Products Directive, is becoming more common and will further accelerate in the near future. It is important that the scope and limitations of EU driven certifications measures are understood [6, 7, 8] and that construction contracts contain appropriate controls.

7.5 5-The structure will be adequately maintained

7.5.1 As is the case with current codes of practice, the partial safety factors for materials denoted in the Eurocodes do not allow for deterioration. Hence it is important that structures are maintained during their life to avoid diminution of the safety margin. This need requires designers to produce a maintenance philosophy strategy or similar statement: CIRIA describes how this might be done [9]. The essence of this advice is that maintenance should be discussed during the design phase and that the client should buy-in to the strategy proposed. The statement should set out the assumptions regarding the nature of maintenance, its frequency and the assumed means of access and egress; it should consider also, as appropriate [10]:

• Costs of design, construction and use
• Costs arising from hindrance of use
• Risks and consequences of failure of the works during its working life and costs of insurance covering these risks
• Planned partial renewal
• Costs of inspections, maintenance, care and repair
• Costs of operation and administration
• Disposal
• Environment.

7.5.2 BS EN1993-1-2 (Fire) Clause 1.3 adds the comment that 'any passive fire protection systems taken account of in the design should be adequately maintained'. Hence for this to be realised the required actions must be passed on to the client, or those responsible for maintenance. In the case of buildings, the Approved Document for Part B requires the designer to make appropriate information available to those in charge of the building in order that the Regulatory Reform (Fire Safety) Order 2005 may be complied with.

7.5.3 Such considerations are supported by the requirements of CDM 2007 in respect of the need to eliminate safety hazards and reduce risk, to pass on information, and to contribute to the Health and Safety File. It is anticipated that the client interaction suggested will encourage discussions on 'capital' versus 'whole-life' costs.

7.5.4 A key element of any maintenance regime is 'inspection', the detail of which will vary, structure to structure. Specific structures already have detailed guidance in respect of maintenance e.g. car parks [11] and bridges [12].

7.5.5 In all cases the client should clearly understand the safety implications of failing to implement maintenance in a competent manner.

7.6 6-The structure will be used in accordance with the design assumptions.

7.6.1 Structures may be designed to a client's specific requirements or to general standards. However, in neither case is the client likely to appreciate the engineering limitations on the structure.

7.6.2 This Eurocode assumption will require designers to schedule the key design assumptions regarding:

1. Its 'Use' (as assumed in the design)
2. Design life
3. Design actions
4. Means of achieving resistance to progressive collapse
5. Details of any special (project related) actions considered.

7.6.3 This data should feature as part of the Health and Safety File, if there is one, or communicated to the client in some other way in other cases (preferably via the drawings).

Summary

8 If current designs are given as being 'in accordance with a specified BS' it infers that measures have been taken to ensure compliance with the assumptions given in the Foreword and Introduction of the named code. Evidence suggests that this is not always done.

The advent of the Eurocodes provides a useful opportunity to remind ourselves of these assumptions and to have particular regard to the six assumptions given in BS EN1990. This Appendix is intended to be an initial attempt to identify the key issues.

Footnote

1. This requires one person to have overall responsibility for structural stability. It is noted that the Eurocodes do not have any similar explicit requirement.

References

1. Carpenter, J. Reflections on structural safety. The Structural Engineer, Vol. 80, No. 8, 16 April 2002, pp11-12
2. Appendix A of this report
3. Health and Safety Executive. Managing health and safety in construction: Construction (Design and Management) Regulations 2007: approved code of practice. Report L144. HSE Books, February 2007
4. Standing Committee on Structural Safety. 15th Biennial Report, Section 4.3.19 at www.scoss.org.uk/publications 5. Carpenter, J. Designing for safe construction. The Structural Engineer, Vol. 84, No. 10, 16 May 2006, pp 17-18
6. For example see www.communities.gov.uk/index.asp?id=1131335. Also see: CE marking under the Construction Products Directive. Updated 2004 7. Guide to be published by Building Research Establishment in 2007.
8. Standing Committee on Structural Safety. 15th Biennial Report, Section 4.3 at www.scoss.org.uk/publications
9. Iddon, J. and Carpenter, J. Safe access for maintenance and repair. C611. CIRIA, 2003
10. Gulvanessian, H. Calgaro, J-A. and Holický, M. Designers' Guide to EN 1990 Eurocode: Basis of Structural Design. Thomas Telford Ltd, 2002, p27
11. National Steering Committee for the Inspection of Multi-storey Car Parks. Recommendations for the inspection, maintenance and management of car park structures. Thomas Telford Ltd, 2002
12. Roads Liaison Group. Management of highway structures: a code of practice. London, TSO, September 2005