Effective second moment of area of uniform built-up members

For built-up compression members, Eurocode 3 in part EN 1993-1-1 [1] includes the shear stiffness to account for the effect of shear deformations directly into the amplification factor when determining second-order forces. Built-up members loaded in bending are not treated at all in EN 1993-1-1 [1]. This article is based on a study [2] performed at Eindhoven University of Technology and introduces the concept of effective second moment of area to account for the influence of the finite shear stiffness of built-up members. This article is largely based on [3] but is an updated and improved version. The effective second moment of area is checked by numerical models. The shear stiffness is derived for a simple configuration of a battened built-up member and for more complex configurations and for laced built-up columns shear stiffnesses are presented. The design rules for built-up compression members in EN 1993-1-1 [1] are analysed and suggestions for modifications are made to include the concept of the effective second moment of area. It is advantageous that the concept of the effective second moment of area can be used for both built-up columns and beams. For built-up beams, the effective second moment of area including the shear stiffness allows the deflections to be calculated with the standard rules for flexural bending.