Flexural Buckling of High-Strength Steel Columns

The European standards dealing with design rules and recommendations for steel structures have been under revision in the past years due to the increased use of high-strength steels. High-strength steels popularity increased at a steady pace in the last decades since they allow for more light-weighted solutions than conventional steels. However, the material reduction ultimately increases the structural slenderness, which in turn has implications on the load bearing capacity if not properly accounted for. Flexural buckling is one of the main challenges steel structures are faced with in order to ensure an economic design. The European design standard EN 1993-1-1 uses an equivalent imperfection factor based on section type, fabrication method and steel grade for the flexural buckling resistance design of a steel member. The European design standards contain guidelines for the selection of the imperfection factor for structural elements made of steels with nominal yield strength up to and including 700 MPa. However, the current design codes are mainly based on tests performed on steels with nominal yield strength below 460 MPa. As higher steel grades are being more commonly used due to their increased global availability, design rules need to be revised and validated. The design standards in force in Europe and in USA do not provide additional rules for steel with nominal yield strength above 700 MPa. The applicability of the current design rules to higher steel grades needs to be assessed as new design standards are being prepared in Europe.This thesis focuses on the weak axis flexural column buckling resistance for high-strength steel sections aiming to propose a general design model to be applied to both mild steels sections and high-strength steel sections. The background, aim and the limitations of the study are explained in the first chapter. In the second chapter, a literature review was presented in which the limitations and the implications of the existing design models were analysed and discussed. Experimental data was collected from available literature in order to identify the need of a new model. The literature review revealed that a general agreement was found between the researchers stating that the European buckling curves are more conservative for columns made of high-strength steel than those made of mild steels and that a change can be justified for welded and cold-formed high-strength steel columns. A similar agreement was found stating t