Structural behaviour of thin-walled steel elements with geometric and sectional non-uniformities

This PhD program proposes innovative ideas within a comprehensive and yet umbrella definition as indicated through the title. Above all, this thesis provides a comprehensive compendium of experimental results on a variety of aspects of buckling of thin walled steel elements and an invaluable resource of experimental data for the later studies of such structural elements. This thesis experimentally investigates the structural stability of thin-walled steel members with different geometrical and material specifications. For tubular circular members made exclusively from steel, large imperfections in the form of dents were examined under axial loading, bending and external pressure. As another form of geometrical irregularity, different shapes and geometries of cutouts were considered in order to investigate the effect of these imperfections on the structural behaviour of the steel members. Circular shell elements with normal fabrication-related imperfections were investigated under external pressure. Reinforcement of the shell members with additional elements (stiffeners/thickeners) and without additional material (corrugation) was also undertaken. Large imperfections such as dents and cutouts with different sizes were then examined for circular tubes under cyclic loading. Rehabilitation of members with cutouts (using Carbon Fibre Reinforced Polymer, CFRP), fully recovered the reduced capacity resulted from the existence of the cutouts; yet, employed reinforcements manifested capacities well above the intact models. Sectional irregularity was also of a great interest in this PhD thesis, which was adopted for composite members. Composite elements such as CFRP and timber were combined with thin-walled steel members to produce light-weight elements with great structural efficiency. Timber cores with different cross sections were utilised for timber filled CHS steel tubular sections. CFRP reinforced the timber-filled CHS members from outside the steel so that both inward and outward buckling was restricted. The same scenario was used for the CHS members with timber and concrete cores, in which the timber blocks were employed to act as compressive members, alongside their key role to form (cast) the concrete inside the tubes. Bending members including timber, reinforced by U-shape steel members were designed in order to make a light-weight flexural element. The effect of such strengthening on the capacity as well as the ductility of the beams in question was evaluated.