Geology Reference
In-Depth Information
Table 1. Earthquake design levels in Vision 2000
(SEAOC, 1995)
ity (a system level indicator) and to the amount
of local deformation imposed on the vertical ele-
ments and beam-column connections (component
level indicators).
In this study the structural performance is de-
fined in three levels: immediate occupancy (IO),
life safety (LS) and collapse prevention (CP); and
these performance levels are mapped onto the
three hazard levels with return periods 75, 475
and 2475 years, respectively. The attainment of
each performance level is described by reaching
or exceeding a threshold value that defines the
respective performance level (or structural limit
state). It is noteworthy that the mapping between
the performance and hazard levels does not indi-
cate that the respective hazard level is considered
only in evaluating the probability of attaining
a given performance level. As described in the
next section on the LCC model, first the fragility
curve is derived and then it is integrated over the
entire range of the earthquake intensity measure
to obtain the probability of reaching or exceeding
each structural limit (or damage) state.
The structural capacity and earthquake demand
are coupled. In other words, the capacity of a
structure is not independent from the earthquake
Earthquake
Design Level
Return Period
Probability of
Exceedance
Frequent
43 years
50% in 30 years
Occasional
72 years
50% in 50 years
Rare
475 years
10% in 50 years
Very Rare
970 years
10% in 100 years
wood. System performance levels were described
in terms of local (individual element) performance
levels.
It is concluded from the review of documents
Vision 2000 and FEMA 273 that conceptually
PBSD framework is very similar. In other words,
it is agreed that seismic design should be based
on multiple performance objectives for stated
earthquake hazard levels, however, the definition
for earthquake design and performance levels
show considerable variation. Furthermore, there
is consensus neither on metrics to be selected as
the indicators of performance levels, nor their
relation to different damage states. However,
interstory drift is mostly preferred since it is
closely related to the development of P-Δ instabil-
Figure 4. Recommended performance objectives for buildings in Vision 2000 (Adapted from SEAOC, 1995)
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