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