2nd generation Eurocode 2
EN 1992-1-1 and EN 1992-1-2 for “The Design of Concrete Structures” (EC2) were formally published in 2004. In the UK, the National Annexes for the documents were published at the end of 2005. Whilst there have been amendments since, these have either been editorial or to address specific problems, rather than significant revisions to the code. The documents are therefore 19 years old and in need of an update. Nothing happens quickly in standard development and plans to update the document started in 2010! Work on technical changes began in 2014 and this page will look at the revision process and highlight some of the changes.
The revision process
The first activity in the revision process was to carry out a “Systematic Review” in which the CEN member nations were asked to provide comments on the current code. This review then provided the background for updating the current clauses. In addition to this, proposals were made for new topics to include in the revised codes. The work was split between 10 voluntary task groups who in turn handed their initial work to three project teams. The first project team worked on improving the current content of EN 1992-1-1, the second project team worked on the fire part, EN 1992-1-2, and the third project team developed clauses for the new topics proposed for EN 1992-1-1. Once the project teams had finished their work, the texts were passed back to the main European Standards Committee for Structural Concrete where they were discussed and further edited after national comments. In July 2021 a draft of the 2nd generation Eurocode 2 was published for CEN Enquiry. This is a formal part of the process and is meant to be the last opportunity for technical comments. The Enquiry stage was passed in December 2021 but there were nearly 5,000 comments received. Once these comments were addressed the 2nd generation Eurocode was sent for Formal vote which was passed at the end of the summer 2023. Leading to final publishing of the 2nd Generation Eurocode 2 by BSI at the end of November 2023.
The technical update
The current EN 1992-2 covering concrete bridges, has been incorporated into the main part, as has EN 1992-3 on liquid retaining and containment structures. It was felt that most of the information in these parts could also be applied to other types of structures. Once this information was removed the remainder did not warrant a separate document and is instead included in Annexes in the main document.
The systematic review clearly highlighted shear, cracking, anchorage and lap lengths as being areas for improvement. The work on shear has led to the proposal of completely new models for members without shear reinforcement and for punching shear, these models are mechanically based and therefore offer more flexibility in use. Whilst the beam shear model retains the basic approach of the current code, there are various more rigorous options to improve the efficiency of the design. The comments on cracking were largely on the simplified approaches and these are moved to an “Informative” annex. As with the current EC2, nations can choose to use, to modify or to simply not use “Informative” annexes. There is now a simplified approach for laps and anchorages, which is similar to that previously used in BS 8110, and a more detailed method is given when the situation is outside of typical cases.
There has been an attempt to reduce the number of different concrete “efficiency” factors used within the code, this is achieved by introducing a so called “brittleness” factor within the design concrete strength. This also has the advantage of simplifying the section design for higher strength concretes. Headed studs and headed bars have been fully incorporated into the detailing rules recognising that they are now commonly used. There is a new annex that covers restraint cracking in a similar framework to CIRIA C766, although there are some significant differences.
One of the changes to EC2 is the introduction of Exposure Resistance Classes (ERC) for durability. The UK do not currently use the method of durability design given in EC2 as this is subject to National Annex and we refer to BS 8500. The new approach can be matched more closely to that in BS 8500 in that for a concrete with a defined ERC, a minimum cover for durability is given. In the UK, initially the approach in BS 8500 will be adopted but in the future the aim is that new and novel, potentially low carbon, concretes can be given an ERC based on a set of accelerated tests thus enabling their easier introduction.
The 2nd generation Eurocode 2 now includes Annexes on non-linear analysis procedures, assessment of existing structures, strengthening of existing structures with CFRP, embedded FRP reinforcement, steel fibre reinforced concrete structures, recycled aggregate concrete and stainless reinforcing steel. With the exception of stainless reinforcing steels, all of these annexes are “Informative”. There are various reasons for this informative status, sometimes this was because of differences in national approaches, but often it was due to the lack of harmonised material standards or execution standards. In some cases, such as assessment of existing buildings, it is recognised that a nation’s building stock reflects the codes they were previously designed to, so there is clearly a place for additional local guidance.
The 2nd generation Eurocode 2 is a significant revision to the current code. Not only does it update many areas in the current code, it also has a much wider scope. Whilst the wider scope has meant some models have become more complicated to allow for the more general application hopefully the new code will prove a competent document for the next 20 years.