Structural Eurocodes: A lowdown

What are the structural Eurocodes?The Eurocodes are a set of common technical rules for the design of buildings and civil engineering. There are 10 Eurocodes covering: basis of design, loading, the main structural materials, seismic design and geotechnics. Their reference numbers - EN 1990 to EN 1999 - are prefaced with BS when issued in the UK (table 1).

List of the Structural Eurocodes

Eurocode BS EN 1990 Basis of structural design

Eurocode 1 BS EN 1991 Actions on structures

Eurocode 2 BS EN 1992 Design of concrete structures

Eurocode 3 BS EN 1993 Design of steel structures

Eurocode 4 BS EN 1994 Design of composite steel and concrete structures

Eurocode 5 BS EN 1995 Design of timber structures

Eurocode 6 BS EN 1996 Design of masonry structures

Eurocode 7 BS EN 1997 Geotechnical design

Eurocode 8 BS EN 1998 Design of structures for earthquake resistance

Eurocode 9 BS EN 1999 Design of aluminium structures

The codes are split into a total of 58 parts. Each part has its own UK national annex with nationally determined parameters (NDPs). While engineers in all participating countries will design following the same principles and design methods, NDPs allow some adjustments to be made to suit local conditions and practices. The NDPs can vary significantly from the recommended values in the code and it is therefore important that the codes are read with the appropriate national annex.

Why have we got them?The Eurocodes can trace their history back to the Treaty of Rome in 1976. Their origin was commercial rather than technical, being introduced to support a Common Products Directive (CPD) which was intended to break down barriers to trade throughout the European Economic Area. However, the design codes that have resulted are generally considered to be the most technically advanced suite of technical standards in the world.

How are they being implemented?A European Directive requires that all conflicting national standards are withdrawn on 1 April 2010. In practice, this means that the British Standard committees responsible have been disbanded and that there will be no further updates to the old standards.

A Public Procurement Directive also requires that from 1 April, all public funded projects must be designed to Eurocodes or a technically equivalent standard. There is some question as to how we could demonstrate the equivalence of another standard and as a result it is generally accepted that all new public projects must be designed to Eurocodes.

Somewhat surprisingly, the Building Regulations for England and Wales will not list the new standards as approved documents but will continue to list the withdrawn standards until at least 2013 when a revision to Part A of the regulations is due to be issued. However, Building Control departments have been instructed to accept designs to Eurocodes.

1 April 2010 is not therefore a magic date when everything changes. It is clear that the switch of codes must happen, but it is likely to take place over a number of years starting with public funded projects.

What difference does it make to organisations?Larger organisations that are used to delivering projects around the world will be familiar with designing to a variety of codes. As a result, the change may possibly come as less of a shock for them than for some smaller organisations.

The underlying principles of design have not changed with the exception of the change from permissible stress to limit state design for timber and geotechnics. Limit state theory is not new to engineers, having been a part of concrete design since 1972; by assessing the state of a structure or element against failure conditions it allows a statistical approach to be taken to design safety, balancing economy and reliability to achieve safe and efficient designs.

On the other hand, the layout and style of the codes is very different and there is a new language to be learned. For example, we will start to talk about “actions” rather than forces, which may be “permanent or variable” rather than “dead or live”.

It is clear that some training for engineers will be necessary in all organisations. The per-capita cost of training should be similar for large and small organizations.

Timing of training is an important consideration. Familiarity will only come from using the codes to design real projects so it is important that training is followed closely by work on actual projects. There is no point in having staff trained and ready to go while design software and design guides are not available.

In WSP, we have already trained engineers who are involved in projects which the client has specified must be designed to Eurocodes. We judge that the time is right to move to Eurocodes more generally, now, and a programme of training is being rolled out to all structural engineers over the next three months, covering basis of design, loading and design in the more common structural materials.

What are the implications and ramifications?Most commercial organisations will be concerned about the impact that introduction of the new codes will have on productivity and delivery. There is a learning curve with any new design code and project delivery must be affected in the short-term; only the most understanding of clients would accept this as a good reason for delay or additional cost to their project and it is therefore something that the design organisation must manage internally. It will be important that quality systems and review procedures are all in order to ensure that mistakes are not made.

Clients are probably most interested in whether the structures designed to Eurocodes will be more economical than those designed to British Standards. The message to be communicated is that there should not be a step change. Modest economies may be achieved in some areas but it is generally accepted that the withdrawn British Standards were neither over-conservative nor unsafe, and therefore the results of design to either set of standards are likely to be very similar.