The Structural Engineer > Archive > Volume 85 (2007) > Issues > Issue 23/24 > Shear enhancement at short shear spans in EN 1992
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Shear enhancement at short shear spans in EN 1992

The approach to shear enhancement at short shear spans for members without designed links in EN 1992 has been changed since early drafts. The revised rule works well for cases with single point loads but a number of problems have been identified for cases with multiple or distributed loads. For these, the rule appears to be over-conservative and difficult to use. It is proposed that the shear enhancement rules in EN 1992 are not applicable for the design of members with multiple loads or design for envelopes of load cases and that alternative rules should be provided. The proposed rules are based on the approach adopted in previous drafts of EN 1992. They have effectively been introduced in the UK EN 1992-2 (bridges) National Annex and could possibly also be used in other structures. The rules for short shear span enhancement in members with designed links suffer from many of the same problems but in addition are over-conservative, often more conservative than the normal rules. It appears that the resistance provided by the links to the shear at short shear spans was originally meant to be used in combination with a concrete contribution to the resistance but the current approach has no concrete contribution. It is proposed that this change should be reversed. There are two other ways of getting short shear span enhancement for members with designed links in EN 1992. Strut and tie analysis gives good consistent results but can be difficult to use for many cases. The other method is to use the rule that allows the links in an increment to be designed for the minimum shear in the increment. This rule needs clarification and modification as the restrictions on its use are unclear. It also appears to be over-generous for inclined links but this is being corrected by an editorial change. Paul Jackson, BSc, PhD, CEng, FIStructE, FICE Technical Director, Gifford Stephen Salim, BEng, PhD Engineer, Scott Wilson, Formerly Gifford Jon Shave, MEng, MA, PhD, CEng, MICE Principal Engineer, Parsons Brinckerhoff Steve Denton, BA, PhD, CEng, MICE Technical Director, Parsons Brinckerhoff