Analysis and modelling of the seismic behaviour of high ... - Ingegneria

2. DUCTILITY AND SEISMIC RESPONSE OF STRUCTURES
along both horizontal directions. Since the numerical model takes into account
directly effects of the material inelastic response, the calculated internal forces will
be reasonable approximations of those expected during a design earthquake.
2.5 Available ductility concept
In an effort to develop methods based on ductility it is clear that the evaluation of
the inelastic response is required. For moment resisting frames (MRFs), inelastic
deformations correspond to the formation of plastic hinges at localized positions
(Gioncu, 200). Available ductility is therefore associated with the rotation capacity
of plastic hinges. The design philosophy must consider that inelastic deformations
occur in one or more of the three components of a node i.e. beam or column ends,
connections and panel zones (Figure 2.12).
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Figure 2.12. Components of a frame node
Modern codes impose that plastic deformation must occur only at beam ends and
column bases, without considering joint panels, even if it is well-known that these
show a stable behaviour under plastic shear deformations (Eurocode 8, 2002). But
in reality the required conditions (the joint capacity must be 30% stronger than the
adjacent members) do not assure the elastic behaviour of joints and as a
consequence, the panel zone can be in some cases the weakest component of a
joint. Results of the so called weak panel zone–strong column system (WP–SC),