Typically, sway imperfections refer to the out-of-plumbness of structural frames and are a key modelling requirement in
design by geometrically nonlinear analyses with imperfections (GNIA). Equivalent geometric imperfections, accounting
for the combined influence of initial geometric imperfections, the spread of plasticity and residual stresses, are used for
modelling convenience. In EN 1993-1-1, the equivalent member bow imperfection amplitudes for use in design by GNIA
e0,GNIA are dependent on the imperfection factor α (i.e. the assigned buckling curve), the material parameter ε, the axis
of buckling and the type of cross-section resistance check to be performed. By contrast, for equivalent sway imperfections
ϕ0,GNIA, two constant values – one for elastic and one for plastic cross-section checks – are provided. The dependency of
e0,GNIA on the imperfection factor α and the material parameter ε rightly reflects the varying influence of residual stresses
and material grade on member buckling. However, sway buckling is also influenced by residual stresses and material
grade; the suitability of the current EN 1993-1-1 provisions for ϕ0,GNIA is therefore questioned. In the present paper, new
equivalent sway imperfections suitable for use in the design of steel and stainless steel structures by GNIA ϕ0,GNIA are
proposed. The new proposals are shown to be able to provide improved capacity predictions, particularly for stainless
steel structures, and are recommended for inclusion into future revisions of Eurocode 3.