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AD 416: Artificially reducing the effective width of slab to satisfy shear connection requirements

In composite construction, the effective width of slab to be used in composite beam design, as calculated from BS EN 1994-1-1 (clause and the former BS 5950-3.1+A1, is based on results from experimental and analytical studies. In the past, designers would sometimes use a smaller effective width in their design in an attempt to satisfy the minimum degree of shear connection requirements (BS EN 1994-1-1, This method has been a matter of controversy as it could lead to situations where the actual number of studs provided is not adequate.

The minimum degree of shear connection requirement is a complex problem which is associated with the overall behaviour of the composite beam, and the stiffness and ductility (slip capacity) of the shear connectors. Therefore, due to the various unknowns and nonlinearities present, it is difficult to justify a relaxation to the codified requirements for a minimum degree of shear connection without proper analysis. For example, a number of parameters have been known to have an effect on shear connection demands such as the span, any asymmetry in the steel flange areas, the steel grade, the construction method (propped vs unpropped) and the utilisation of the beam in bending. As one can imagine, simplified methods such as the one in question cannot possibly account for all these in a quantifiable manner.

The most recent guidance in SCI P405 was developed based on the results from tests and extensive numerical analyses that accounted for the effects of the above mentioned parameters. A set of alternative shear connection rules that cover different practical cases is provided to complement the rules in BS EN 1994-1-1.

Contact: Dr Eleftherios Aggelopoulos
Tel: 01344 636555

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