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

1. INTRODUCTION
detailed for inelastic behaviour. All other structural elements are protected against
actions that could cause failure by providing them with strength greater than that
corresponding to the development of the maximum feasible strength in the plastic
hinge regions. The following features characterise the procedure:
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• potential plastic hinge regions within the structure are clearly defined and
designed to have dependable strengths and ductility;
• potential brittle regions, or those components not suited for stable energy
dissipation, are protected by ensuring that their strength exceeds the
demands originating from the overstrength of the plastic hinges.
To highlight the concept of capacity design, the chain shown in Figure 1.1 is often
considered (Plumier, 2000). As the strength of a chain is the strength of its weakest
link, one ductile link may be used to achieve ductility for the entire chain. The
nominal tensile strength of the ductile link is subject to uncertainties of material
strength and strain hardening effects at high strains. The other links are presumed
to be brittle, but their failure can be prevented if their strength is in excess of the
real strength of the ductile weak link at the level of ductility envisaged. Correct
application of the capacity design principle thus requires knowledge of the material
properties, both of the plastic and neighbouring zones, and the evaluation of the
stresses and strains, which must be sustained by the material of the plastic zones.
It is clear now that pre-Northridge or Kobe design was characterised by
weaknesses in the evaluations made either on the side of resistance or on the side
of action effect.
Figure 1.1. Principle of capacity design
Solutions assuring the necessary ductility can be obtained not only through careful
study of building morphology, structural schemes and construction details, but also
through the rational use of materials. Steel-concrete composite structures, owing to
their high capacity for prefabrication and rational use of the materials, seem able to
provide high levels of performance in terms of ductility and dissipation energy,
while at the same time containing construction costs. However, the adoption of
such structural solutions in design practice has been precluded to date by the lack
of suitable constructional solutions. In fact, Eurocode 8 (prEN 1998-1, 2002) sets
forth general principles for designing composite structures for seismic areas and