Ground Motions and Structures - Earthquake Engineering for Structural Design - page 322

322 Earthquake Engineering for Structural Design

A measure of the overall structural ductility is given by the local material, member
and joint ductility. The material ductility corresponds to the ability of a material to
undergo large plastic deformation before rupture. The element or joint ductility
characterizes the ability to carry out and transmit stresses to the neighbouring elements
in elasto-plastic range without loss of resistance.
A framed structure cannot exhibit a ductile behavior if the plastic hinges formed at
the member ends have not enough rotation capacity, being able to redistribute the
bending components (Fig. 8.24). Therefore, the analysis of the behavior of plastic
hinges became of primary interest (Gioncu and Mazzolani, 2002). The limitation of the
rotation capacity is the result of the plastic local buckling of the compressed parts of
the cross-section. There are three methodologies to evaluate the ability of plastic
hinges to develop an adequate rotation capacity:
- introducing cross-sectional classes (Fig. 8. 25a), which limit the slenderness of
the compressed parts of the cross-section, in order to eliminate local buckling effects.
Four classes are proposed, corresponding to plastic, compact, semi-compact and
slender sections. This methodology is used in the majority of the modern design codes,
being very simple and friendly;
- using member behavior classes, which considers the plastic rotation capacity of
members (Fig. 8.25b) (Mazzolani and Piluso, 1993). Three classes of ductility are
proposed: high ductility, medium ductility and low ductility, in function of the

Figure 8.24 Rotation of plastic hinges and structure ductility
(Gioncu and Mazzolani, 2002)