Development of a new design method for steel hollow section members resistance

This dissertation presents research done in the field of enhancing the performance and the carrying capacity of tubular members, through the development of an original design approach based on the “Overall Interaction Concept” (O.I.C.). The proposed approach makes use of the interaction between the two ideal behaviours of structural members (resistance and instability) and includes the influence of initial imperfections (out-of straightness, residual stresses, non-homogenous material), to calculate the resistance of a structure through a single parameter: “relative slenderness”.
A test program was carried out as a part of a European project named ‘HOLLOPOC’ to determine the experimental behaviour of beam-columns loaded by bi-axial bending with axial force. Twelve buckling tests, consisting of hot-rolled and cold-formed rectangular and circular hollow section members were conducted. These tests were accompanied by preliminary measurements of cross-section geometry, material properties, geometrical imperfections, residual stresses as well as stub column tests. Besides, a finite element model was calibrated on the basis of these tests. For both the present test series and another one from the literature, it was shown that the FE models were capable of replicating accurately the response and resistance of the experiments. Accordingly, the validated FE models have been further used in extensive numerical studies, and a database comprising more than seventy thousand results was built consecutively. Based on these computations, design proposals were made, by considering identified governing parameters, within the context of the Overall Interaction Concept, using an extension of the Ayrton-Perry approach. Finally, a safely evaluation was completed to check the proposed formulae against the results of current Eurocode 3 rules.