AD 424: Shear stud length
SCI has been advised that shear studs which are shorter than usual have been placed on the market in the UK, and this AD warns against using them unless the length has been reflected in the design, and unless the studs meet the necessary material specification.
AD 380 indicates that a stud that starts with a manufactured length of 105 mm would typically have a length after welding (LAW) of 100 mm when welded directly to a beam flange and 95 mm when welded through decking. The studs are identified as nominally 100 mm studs. AD 380 also indicates that studs of diameter d = 19 mm and a nominal length of 100 mm may be deemed to satisfy the requirement that a stud extends at least 2d above the height of the decking, when that height is 60 mm. UK practice in composite construction for buildings generally involves the use of through deck welded shear studs. Tests have shown that through deck welded studs of 100 mm nominal length, with 60 mm decking, perform satisfactorily.
A complication is that studs identified as nominally 100 mm long have actual lengths “out of the box” which differ from manufacturer to manufacturer. It is understood that the shorter studs referred to in the opening paragraph are 90 mm before welding, so are likely to be less than 85 mm LAW when welded through decking. Clearly they should not simply be substituted for nominal 100 mm studs unless the design is verified with the shorter length.
All shear studs should conform to EN ISO 13918, as noted in the National Structural Steelwork Specification (NSSS). Composite beam design generally assumes a certain level of slip between the steel and concrete so the studs must be ductile, regardless of the fact that failure is normally in the concrete (at least for the grades of materials typically found in buildings). Annex B of BS EN 1994-1 describes the stud test arrangement to demonstrate ductility.
Contact: Eleftherios Aggelopoulos
Tel: 01344 636525