Corrigendum for Eurocode 2
Jones, Tony
BSI has now issued a corrigendum to EN 1992-1 (Eurocode 2)(1). The correction will eventually be incorporated into a new version of EC2. However in the interim those using EC2 should be aware of the changes.
The BSI corrigendum is 22 pages long and includes over 130 changes. While this will undoubtedly be used by some to further criticise the Eurocode system, this document attempts to put the changes in context and highlights the very few changes that are likely to have general technical impact. Those using EC2 for formal design should refer to the full corrigendum to ensure that more minor issues are picked up.
Nature of changes
The changes can be conveniently split as follows:
Corrections to the cross-referencing – in a document that cross-refers as often as a code of practice, that was revised many times in the final editing and is as long as EC2, it was inevitable that there would be some mistakes. Normally these are relatively obvious, with the clause number referred to not existing or being clearly irrelevant to the check in progress.
Corrections to subscripts for conformity – in a number of clauses a lower case subscript is changed to an upper case subscript to comply with the agreed formatting across the Eurocodes. These changes are of no practical technical consequence.
These two sets of changes make up the majority of the corrigendum. Other types of change are:
Corrections due to typographical errors – these range from incorrect use of upper case letters, changes of wording, through to the potentially more significant further correction of subscripts. Even in the latter case the changes are normally to add clarity rather than to correct an error, for example in the plain concrete section^ has been changed to f^sub cd,pl^ pi to emphasise that it is the design compressive strength for plain concrete that should be used.
Corrections to figures – these are normally required to provide consistency with the text.
Changes of general technical impact
As noted in the introduction, this section is not meant to describe every change that may have a technical impact but to highlight those changes that will have a more general impact.
Cl 4.4.1.3(4): For concrete cast against the ground the term ‘minimum cover’ has been changed to ‘nominal cover’; this means the allowance for cover deviation no longer needs to be added to the covers given. It should be noted that the UK National Annex(2) reduced the values recommended in EC2 to allow for the cover deviation; therefore now that EC2 has been corrected, the change in the National Annex should be ignored. The outcome of this is that, in the UK, this correction will have no effect once the UK National Annex is updated.
Cl 5.8.8.2(2): The simplification for calculating an equivalent first order end moment has been clarified as only being applicable to members without applied loads between their ends. This issue is covered more extensively in PD6687:2006(3) and this emphasises the benefit of referring to such background documents during the implementation of EC2.
Cl 5.10.2.1(2): The existing clause compares the maximum prestressing force with a proportion of the 0.1 % proof stress of the prestressing steel. Clearly, to get a force the stress needs to be multiplied by the area of prestressing steel and the corrigendum confirms this.
Cl 6.2.3(6): The corrigendum clarifies that this clause is only applicable to grouted metal ducts.
Cl 6.2.5(2): The corrigendum significantly downgrades the contribution of the concrete tensile strength to the interface shear capacity for smooth and very smooth surfaces. For very smooth surfaces a range of values is given due to the variability of finishes possible. This will not be helpful for the designer who will need to take the lowest value unless data for the specific situation are available. There is a more minor downgrading of the contribution of the concrete tensile strength for rough surfaces.
Cl 11.6.1(1): A reduction factor related to density has been added to the expression for minimum shear strength of lightweight concrete sections. The same factor has been removed from Cl 11.6.2(1). In addition in the note to Cl 11.6.1 the minimum shear strength has been corrected. This later point was also corrected in the UK National Annex. Unfortunately the corrigendum and the National Annex do not agree; the difference, however, is light and the designer should probably use the slightly more conservative corrigendum value.
Table 11.6. 1N: A correction to one cell of the table is required. While this reduces the minimum shear strength for this situation, inspection of the surrounding values would have alerted an engineer to this potential problem.
Cl 12.9.3(1): The expression for defining the geometry of unreinforced strip and pad footings has been modified leading to more efficient designs.
Concluding remarks
While the corrigendum to EC2 is a relatively long document, most of the changes are related to improving the editorial consistency of the document and will have little practical technical impact. This note has highlighted eight areas where there is a potential technical impact but, as discussed above, several of these issues have already been addressed in the UK National Annex and PD 6687. Several further areas are in sections of the code less frequently used (eg, lightweight concrete and plain concrete) and in several more areas the errors should have been obvious to those with some experience of reinforced concrete.
The issuing of the corrigendum should be seen as a positive indication of the intent to maintain and improve EC2 rather than a reason to criticise the Eurocode system.
References:
1. BRITISH STANDARDS INSTITUTION. BS EN 1992-1-1. Eurocode 2: Design of concrete structures – Part 1-1: General rules and wies for buildings. BSI, 2004.
2. BRITISH STANDARDS INSTITUTION. NA to BS EN 1992-1-1. Eurocode 2: Design of concrete structures – Part 1-2: General rules – Structural fire design. BSI, 2004.
3. BRITISH STANDARDS INSTITUTION. PD 6687. Background paper to the UK National Annex to BS EN 1992-1-1 and BS EN 1992-1-2. BS1, 2005.
TONY JONES, ARUP
Copyright The Concrete Society Oct 2007
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