Abstract:
In the recent codes for the design of steel structures, the elastic–plastic methods of analysis are
recognised to provide an efficient estimation of the ultimate resistance of some of these structures.
These methods are usually based on some basic hypotheses, such as the creation of plastic hinges in the
most stressed cross-sections, for instance.
As the development of these plastic hinges depends on the interaction between the internal forces
and on the cross-section shape, specific equations are required for the analysis of different types of
cross-sections. However, most frequently, these equations are not available, or they are expressed by
means of simplified expressions; this is usually the case when biaxial bending is involved.
This paper presents new interaction criteria for the analysis of steel rectangular hollow sections
subjected to an axial force and biaxial bending moments, at the elastic or the plastic limit states (as long
as buckling phenomena are not involved). The plastic interaction criteria are presented, in a first step,
for some particular combinations of the internal forces, such as axial loading with bending about a main
axis, and biaxial bending without axial loading. Then, the global solution for the simultaneous
combination of an axial force and bending moments about both the main axes of inertia are described
in detail. All these plastic interaction criteria are compared with the corresponding plastic criteria
adopted in the Eurocode 3 (EC3). Some suggestions are presented in order to improve the results given
by these EC3 criteria.
