Expressions to predict the rotation capacity of austenitic stainless steel members under constant axial load and cyclic bending

Stainless steel is a structural material with increasing demand for its aesthetic and mechanical properties, as well as its potential in seismic design due to its ductility and strain hardening. However, research on the behaviour of stainless steel under seismic loads is scarce, especially when focused on the global response of structures. One of the key parameters governing the seismic response of systems is the rotation capacity of structural members and compacts, for which recent investigations have proposed predicting expressions under cyclic bending. However, in more complex loading cases such as members subjected to constant axial loads (i.e., gravity loads) and cyclic bending (i.e., seismic actions), the existing expressions for predicting the rotation capacity are very complex or only applicable to a limited range of cases. In this context, the present investigation proposes simple analytical expressions to predict the full moment-rotation diagrams of austenitic stainless steel hollow section elements under combined axial loading and cyclic bending. The proposal is based on an extensive numerical parametric study considering a range of elements under different local slendernesses and several levels of axial loading. The rotation capacities and corresponding bending moment resistances are related to the key affecting parameters, such as the axial load, section stiffness and local slenderness, from which the key features of the full moment-rotation diagrams can be obtained for the characterisation of plastic hinges, allowing a more efficient seismic design of stainless steel structures. • The performance of austenitic stainless steel RHS and SHS members under axial loading and cyclic bending is studied. • A parametric study comprising 98 stainless steel column models is performed. • A new susceptibility parameter able to predict the rotation capacity is derived. • Expressions to predict plastic rotation capacities under constant axial load and cyclic bending are proposed. • A tri-linear model predicting the full moment-rotation curve of stainless steel members is presented.