Ductility assessment of structural steel and composite joints

Eurocode 3, in its Part 1-8 on the design of structural joints, and Eurocode 4 provide designers with assessment procedures for the initial rotational stiffness and the resistance of steel and composite joints respectively. These design procedures refer to the so-called component approach and have been validated through numerous comparisons with test results and numerical non-linear simulations. For beam and column members, the resistance level considered by the code is the one which could not be exceeded at ULS and it depends on the cross-section class (Class 1 to Class 4). For Class 1 cross-sections, the plastic resistance may be considered and internal rotations may take place and develop in the cross-section in the case ductility criteria are met. If plastic rotation capacity is available, a plastic global analysis of the structure may be contemplated. For connections and joints, a similar concept is to be applied, but unfortunately very few information is provided in the Eurocodes which would enable the designer to check whether enough plastic rotational capacity is locally available. In this paper, a procedure to estimate the rotation capacity of joints is presented. As for the evaluation of the stiffness and resistance properties, it refers to the component method approach. Its validity is demonstrated through comparisons with experimental data.