Design optimisation of welded I‐beams made of high strength steels

Nowadays, hot rolled steel sections are used in practice. The cross‐sectional dimensions are therefore fixed and catalogued by the steel manufacturers. However, when the span of the members and/or the applied load becomes significant, such hot rolled steel sections can no longer meet the ultimate and/or service design criteria and the use of a built‐up welded I‐beam should be considered. They are typically made of three steel plates welded together to form a monolithic I‐beam. By varying the dimensions of these plates, an infinite amount of cross‐section geometries can be defined. But face to this high variability of solutions, the designers encounter difficulties in identifying the most appropriate combination of geometrical and mechanical properties for the constitutive plates.To study and optimise these profiles, a MATLAB® routine has been developed at the University of Liege. It allows, for different load cases, to find suitable cross‐sectional dimensions that minimise the weight and/or the total cost of the element. This routine follows the current recommendations prescribed in prEN1993‐1‐5 and evaluates the possibility of using transverse stiffeners along the web to further reduce the weight and cost of the element. The so‐developed routine is presented in the present paper. Also, the advantage of considering the use of high strength steels for such structural members is discussed to propose recommendations to the designers for the selection of the most appropriate steel grade.