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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4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS<br />
<strong>the</strong> specification <strong>of</strong> a performance level <strong>and</strong> an acceptable low probability that<br />
poorer performance could occur within a specific period <strong>of</strong> time. To evaluate a<br />
performance objective, selection <strong>of</strong> a performance level <strong>of</strong> interest is required. The<br />
performance levels can be, for example, <strong>the</strong> ultimate state limits or <strong>the</strong> service<br />
state limits. A desired probability that damage in a period <strong>of</strong> time will be worse than<br />
this performance level has to correspond for each selected level. Moreover an<br />
average estimate <strong>of</strong> <strong>the</strong> ground shaking intensity at <strong>the</strong> probability <strong>of</strong> exceedance<br />
identified in <strong>the</strong> performance objective definition has to be determined for each<br />
probabilistic performance objective.<br />
The performance <strong>of</strong> a building during an earthquake depends on many factors<br />
including: <strong>the</strong> structure’s configuration <strong>and</strong> proportions, its dynamic characteristics,<br />
<strong>the</strong> hysteretic <strong>behaviour</strong> <strong>of</strong> <strong>the</strong> elements <strong>and</strong> joints, <strong>the</strong> type <strong>of</strong> non-structural<br />
components employed, <strong>the</strong> quality <strong>of</strong> materials <strong>and</strong> workmanship, <strong>the</strong> adequacy <strong>of</strong><br />
maintenance, <strong>the</strong> site conditions, <strong>and</strong> <strong>the</strong> intensity <strong>and</strong> dynamic characteristics <strong>of</strong><br />
<strong>the</strong> earthquake ground motion experienced. Consequently, <strong>seismic</strong> performance<br />
prediction for buildings, ei<strong>the</strong>r as part <strong>of</strong> a design or evaluation, should consider,<br />
ei<strong>the</strong>r explicitly or implicitly, all <strong>of</strong> <strong>the</strong>se factors.<br />
Therefore, a reliability-based performance-oriented approach, adopted by <strong>the</strong> SAC<br />
project for design <strong>and</strong> evaluation, was taken in order to explicitly account for<br />
uncertainties <strong>and</strong> r<strong>and</strong>omness in <strong>seismic</strong> dem<strong>and</strong> <strong>and</strong> capacities in a consistent<br />
manner <strong>and</strong> to satisfy with defined reliability identifiable performance objectives<br />
corresponding to various occupancies, damage states <strong>and</strong> <strong>seismic</strong> hazards.<br />
Consistently with <strong>the</strong> Eurocode 8 (2002) <strong>and</strong> on <strong>the</strong> basis <strong>of</strong> <strong>the</strong> FEMA 302<br />
NEHRP Recommended Provisions for Seismic Regulation for New Buildings <strong>and</strong><br />
O<strong>the</strong>r Structures (BSSC, 1998a) <strong>and</strong> <strong>the</strong> FEMA 273 NEHRP Guidelines for<br />
Seismic Rehabilitation <strong>of</strong> Buildings (BSSC, 1997), two performance levels are<br />
considered. These are termed Serviceability Limit State (S.L.S.) <strong>and</strong> Ultimate Limit<br />
State (U.L.S.):<br />
• The Serviceability Limit State (named Immediate Occupancy (IO) level in<br />
<strong>the</strong> FEMA Provisions) is defined as <strong>the</strong> post-earthquake damage state<br />
where only minor structural damage has occurred with no substantial<br />
reduction in building gravity or lateral resistance. Damage in this state<br />
could include some localized yielding <strong>and</strong> limited fracturing <strong>of</strong> connections.<br />
Damage is anticipated to be so slight that if it is not found during inspection<br />
<strong>the</strong>re is no cause for concern. For pre-Northridge buildings, fewer than<br />
15% <strong>of</strong> <strong>the</strong> connections on any floor may experience connection fractures<br />
without exceeding <strong>the</strong> IO level.<br />
• The Ultimate Limit State (named Collapse Prevention (CP) level in <strong>the</strong><br />
FEMA Provisions) is defined as <strong>the</strong> post-earthquake damage state, in<br />
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