Probabilistic assessment of ductility for earthquake resistant design of steel members

An appropriate supply of member ductility is an important ingredient for successful earthquake resistant design since it enables the primary objective of a well controlled dissipative collapse mode to be realised, without excessive strength requirements being imposed on non-dissipative components. As with other performance criteria, uncertainties influence the actual ductility supply, with material variability being a key contributor. This paper examines the effect of this variability on cantilever tip deflection ductility, based on an interactive local buckling model developed for steel members subjected to large inelastic excursions. Probabilistic models for yield stress and strain hardening variability are introduced in a FORM reliability analysis, and their influence studied for a wide range of steel beam and column members. The results quantify material variability on member response, and are readily presented for design use through the definition of generalised parameters involving cross-section properties and material uncertainty coefficients.