Behaviour and design of bolted aluminium flange cleats

Equivalent T-stubs are traditionally employed to model the structural behaviour of the tension zone of moment resisting connections. The design model for the equivalent T-stub considers only the bending moments acting on the equivalent T-stub without considering the co-existing tensile force acting on the T-stub web. However, for flange cleats in bending, the horizontal cleat leg (i.e. the T-stub web) at the junction with the vertical leg is subjected to a co-existing tensile force in addition to the bending moment which limits its moment resistance. This is not considered in current design specifications which made them potentially unsafe. This paper reports 5 experimental tests on bolted aluminium angle cleats in grade 6082 T6 that were used to develop and validate a finite element model. Subsequently, parametric studies were conducted over a wider range of flange cleat geometries covering all types of failure modes considered in EN 1999-1-1. The design specifications for equivalent T-stubs in tension set out in EN 1999-1-1 were assessed and cases where the specifications are inaccurate or potentially unsafe were highlighted. A simple modification of the existing design model is proposed, which offers more consistent and safe ultimate capacity predictions.