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Steel Designers' Manual - 6th Edition (2003)
920 Tolerances
31.2.3 National structural steelwork specification (NSSS)
The limitations of the tolerances specified in earlier versions of BS 5950: Part 2 have
been extended by an extensive coverage of tolerances in the National structural
steelwork specification for building construction. This is an industry standard based
on established sound practice. The widely accepted document, promoted by the
British Constructional Steelwork Association (BCSA), is now in its 4th edition.
31.2.4 ENV 1090-1 Execution of steel structures
As part of the harmonization of construction standards in Europe, CEN has issued
ENV 1090: Part 1: General rules and rules for buildings, which is available through
BSI as DD ENV 1090-1: 1998.
This document includes comprehensive recommendations for both erection and
manufacturing tolerances. To a large extent these recommendations are consistent
with BS 5950: Part 2 and the NSSS. However, some of them are more detailed.
31.2.5 ISO 1071-2 Steel structures: Part 2: Fabrication and erection
This is very similar to ENV 1090-1 and BS 5950: Part 2. It is unlikely to be issued
as a BSI standard.
31.2.6 BS 5606 Guide to accuracy in building
BS 5606 is concerned with buildings generally and is not specific to steelwork. The
1990 version has been rewritten as a guide, following difficulties due to incorrect
application of the previous (1978) version, which was in the form of a code.
BS 5606 is not intended as a document to be simply called up in a contract
specification. It is primarily addressed to designers to explain the need for them to
include means for adjustment, rather than to call for unattainable accuracy of construction.
Provided that this advice is heeded, its tables of ‘normal’ accuracy can
then be included in specifications, except where they conflict with overriding structural
requirements. This can in fact happen, so it is important to remember that the
requirements of BS 5950 must take precedence over BS 5606.
BS 5606 introduces the idea of characteristic accuracy, the concept that any construction
process will inevitably lead to deviations from the target dimensions, and
its objective is to advise designers on how to avoid resulting problems on site by
appropriate detailing. The emphasis in BS 5606 is on the practical tolerances which
will normally be achieved by good workmanship and proper site supervision. This
can only be improved upon by adopting intrinsically more accurate techniques,