Structural assessment of minor axis steel joints using photoelasticity and finite elements

Traditionally, the steel portal frame design assumes that beam-to-column joints are rigid or pinned. However, it is largely recognized that the great majority of joints do not exhibit such idealized behaviour transmitting bending moments with non-negligible rotations. These joints are called semi-rigid and their design should be performed according to their actual structural behaviour. When minor axis beam-to-column joints are considered, the adopted design process generally assumes a flexible response although this is not true for the great majority of structural joints. Minor axis joints present a distinct behaviour that differentiates them from major axis joints. In fact, the absence of transverse stiffeners implies that the column web must resist all the tensile and compressive forces arising from the beam flanges in bending, akin to a plate supported on its vertical sides. In order to evaluate this component’s behaviour, this paper presents a comparison between results obtained from a finite element model analysis and experiments. The experimental programme was based on the use of reflection photoelasticity techniques to determine the column web stress and strain distribution present in minor axis semi-rigid joints. This technique, although widely used for determining stress and strain distributions in other applications, was first used in this investigation to determine the semi-rigid joints structural response.