Geology Reference
In-Depth Information
Figure 3. (a) Example hazard curves for different intensity measures obtained from PSHA, (b) design
spectra at different return periods obtained from PSHA (YRP: years return period)
very well defined. The more challenging part is
the definition of structural limit states and their
correspondence to hazard levels. Studies on PBSD
try to answer a similar question.
As opposed to traditional seismic codes that aim
to provide structures with adequate strength and
ductility for life safety, and stiffness for service-
ability limits states, PBSD is a broader approach
where the objective is to achieve stated perfor-
mance objectives (levels) when the structures are
subjected to stated seismic hazard levels. Using the
multilevel (in terms of hazard) and multi-criteria
(in terms of performance) approach offered by the
PBSD it is aimed that the structural design will be
under direct and explicit control and the expecta-
tions of stakeholders for more explicit codes for
defining design objectives will be fulfilled. This
is the very same reason for PBSD lending itself
for use in LCC optimization of structures.
Vision 2000 (SEAOC, 1995) has been one of
the key documents in the development of PBSD
concepts. In Vision 2000, the hazard levels were
expressed in terms of return periods as shown in
Table 1. A performance level was defined as the
maximum allowable damage to a building for a
given earthquake design level. The performance
levels were determined by the condition of both
the structural and nonstructural components.
Four performance levels were defined: fully
operational, operational, life-safety, and near
collapse. Damage states of structural components
were mapped to performance levels. Finally, a
design performance objective was described as
the desired performance level for the building for
each earthquake design level. Design performance
objectives were dependent on the building's oc-
cupancy, the importance of functions occurring
within the building, economic considerations
related to repair due to building damage and busi-
ness interruption, and importance of the building
as a historical or cultural asset. Recommended
design performance objectives for buildings were
mapped onto earthquake design levels as shown
in Figure 4.
In FEMA 273 (FEMA, 1997) a similar frame-
work to that of Vision 2000 (SEAOC, 1995) was
presented. However, different design performance
objectives and earthquake design levels were
adopted (Figure 5). Threshold values for struc-
tural and nonstructural components at various
performance levels were tabulated for various
building types including steel, RC, masonry and
Search WWH ::
Custom Search