Development of a new design method to define the rotation capacity of steel hollow sections

The present PhD thesis is dedicated to the characterisation of hollow section shapes’ rotational capacity. More precisely, the effort was made towards suggesting new ways to resort to plastic analysis, by defining a new and accurate proposition to characterise the rotation capacity Rcap of sections, which could be associated with the rotation demand of a structure Rdem. Therefore, the purpose of this thesis is to establish a direct dependence of the rotation capacity Rcap with a newly defined cross-section slenderness CS. Hence, current design standards disregard the rotation demand of the structure and allow plastic analysis based on a plate slenderness limit.
To achieve this purpose, an experimental campaign was performed consisting in 23 bending tests on square and rectangular hollow sections tested in bending, in addition to 8 stub columns. Then, a numerical model based on the finite element software FINELg was calibrated to well represent these experimental tests, as well as cold-formed bending tests from literature. Based on these results, a good agreement between experimental and numerical results was shown and the numerical software was therefore validated.
Accordingly, since the numerical software was proved to well represent the bending behaviour of hollow beams, around 8000 finite element simulations were performed while varying sections dimensions, material properties and loading configuration. These results reported that actual standards limitations were inappropriate, and stricter values were proposed. Moreover, based on the numerical computations, a continuous curve capable of describing the rotation capacity of sections as a function of the cross-section slenderness was proposed. The production route, loading application and yield strength were identified as key parameters having a major impact on the rotation capacity of sections. Consequently, different curves were proposed for each parameter; based on these curves, the rotation capacity of the section could be compared to the rotation demand of a structure in order to obtain a practical, safe, and reliable design calculation.