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

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