TRADA’s Dr Keerthi Ranasinghe provides an update on the comprehensive Eurocodes design standard and explains why it is still relevant
Structural Eurocodes design standards, comprising ten standards, cover a vast area of knowledge that includes subjects such as the basis of structural design, actions applied to structures, as well as material specific guidelines for structural design. The entire suite comprises of 58 different parts containing thousands of pages of relevant information.
First generation limitations
When the first generation of Eurocodes were published around 2004, they were widely acclaimed to be the most comprehensive set of design standards found anywhere in the world. However, the changeover to the Eurocodes from the familiar National Standards, such as the BS suite of standards in the UK, was not at all smooth in most European jurisdictions. A common argument against the use of Eurocodes was their complexity in comparison to their corresponding National Standards. For example, in the case of timber engineering design in the UK, where the British Standard (BS 5268) used a simple tabulated approach to present information, Eurocode 5 (BS EN 1995 – a suite of three standards covering timber design) opted to use complex equations and formulae instead.
The design philosophy was also changed from permissible stress design to a one involving limit state design. Most engineering practices, therefore, however big or small, initially struggled to cope with this transition. Within this backdrop, the European Commission in December 2012 issued a Specific Mandate (M515) to the European Committee for Standardisation (CEN), with the scope to develop a second generation of Eurocodes to:
- Amend the first generation of Eurocodes, and
- Develop new Eurocodes.
The mandate M515 also gave the directions that the second generation of Eurocodes should:
- Encourage innovations
- Take into consideration new demands and needs of society
- Harmonise national technical initiatives on new topics of interest to the construction sector, and
- Improve ease of use.
In response, the CEN Technical Committee 250 (CEN/TC250 – overarching committee responsible for all structural Eurocodes), under the chairmanship of Professor Steve Denton (Parsons Brinckerhoff and University of Bath) produced a detailed work programme for the development of the second generation of Eurocodes. The technical work under this programme is to be carried out in four overlapping phases, of roughly three-and-a-half year’s duration each. Work under Phase 1 is already underway, aiming to deliver the technical content by 2020.
In the context of timber engineering design, work under Phase 1 is being carried out on the two new topics:
- Cross-laminated timber, and
- Timber-concrete composites.
The work is carried out by two separate Project Teams (PTs) appointed by and contracted to CEN through the National Standardisation body for the Netherlands. Both of these PTs report back on their progress to the Sub-Committee 5 of CEN/TC250 (CEN/TC250/SC5) responsible for timber engineering (Eurocode 5). The UK is well represented in these Phase 1 developments, not only at the sub-committee level but also at the PT level.
Phases 2, 3 and 4
Under Phase 2, for timber engineering design, everything else within Eurocode 5, other than the two topics, timber connections and timber in fire, are to be addressed. Although the PTs are yet to be appointed, some of the items of work identified for this phase are the vibration of floors, robustness and stability of timber frame walls – subjects that are generally considered as being insufficiently addressed by the current Eurocode 5. Phase 3 will then cover the subjects of timber connections and timber in fire, with Phase 4 concentrating solely on timber bridges.
As these timber engineering work packages are to progress in parallel to developments in other structural Eurocodes, for example, the base Eurocode EN 1990 – Basis of Structural Design, a great deal of cross-coordination is taking place as well. This is facilitated by CEN/TC250, through the work of the relevant sub-committees, working groups and horizontal groups. For example, the working groups on timber connections and timber in fire under CEN/TC250/SC5, are already working hard on formulating the background documents on which the project teams, when appointed under Phase 3, should base their work on. TRADA is actively participating in the work of both these working groups. It should be noted that the participation in these committees and working groups is entirely voluntary with no payments being made to the participants.
Over the years, TRADA, through the training courses it offers with its appointed technical services provider Exova BM TRADA, listened to many engineers’ concerns on their use of Structural Eurocodes. One recurring theme that came out during these discussions was the question of ‘Can these standards be simplified?’ This concern has been captured by the EC direction for the second generation of Eurocodes, in that the new standards should improve on ease of use. TRADA, through its representatives at the British Standards Institution (BSI) Committees, as well as the CEN committees and working groups, has always pushed for clarity and simplicity of standards. TRADA continues to voice its members’ concerns at these forums and strives hard to find agreements with European counterparts to produce standardisation solutions that are state of the art, yet easy to follow.
One interesting question recently asked within the current political context is: ‘Do we really have to use Eurocodes now that the UK has voted to exit the EU?’ This is a highly sensitive area of discussion, and it is recommended that readers take guidance from the knowledgeable articles produced by the BSI on the subject, available at www.bsigroup.com/en-GB/about-bsi/media-centre/BSI-and-Brexit
For further information, please read the manual for the design of timber building structures to Eurocode 5, available at www.trada.co.uk/publications
Dr Keerthi Ranasinghe
Principal Structural Engineer
Exova BM TRADA