Geology Reference
In-Depth Information
INTRODUCTION TO
PERFORMANCE-BASED DESIGN
C. Life Safety (LS), in which the structure
tolerates sever damage, but it remains safe
for the occupants to evacuate the building.
D. Collapse Prevention (CP). This level of
performance is the final stage of life of a
structure in which the structure has reached
its instability level, and an increase in load or
deflection results in collapse of the structure.
As was mentioned before, the performance-based
design integrates the design for deformation
with the design for strength. In this new design
philosophy, the “ductility of structure” and the
“resistance for the internal forces” have the same
order of importance. It is expected from the design
engineer, to design the structure in such a way
that it exhibits different desired behaviours under
different intensities of loads. Although this design
strategy is general, it is mainly proposed and used
for design of structure under earthquake excita-
tion. Accordingly in this chapter our discussion
is limited to this field of application.
Although Japanese are likely the first who
proposed and used the performance-based design,
the studies made in the United States of America
are the best known and the most referred ones.
Since this design philosophy is not yet mandatory
for newly designed structures, but is essential in
rehabilitation of buildings, most of research works,
practical recommendations and applications are
made in seismic rehabilitation of buildings. As an
introduction to the research activities in this field,
one may consult a paper by Ghobarah (2001) who
has reviewed the serious challenges up to 2001.
ASCE41 (2007) that is the latest published
recommendations for rehabilitation, considers
four levels of performances for structures. These
performance levels that are virtually adopted
worldwide are:
Depending on the degree of importance of a
structure, it may be desirable to have different
levels of performances for different levels of
earthquake intensities. For example, it may be
desirable to design a hospital so that even for se-
vere earthquake excitations, its performance does
not go beyond life safety (LS) situation. This is
because hospitals are to serve to the people after
earthquake. For a residential building, it may be
uneconomic to be designed similar to a hospital;
therefore, it may be designed such that it experi-
ences CP situation for severe earthquakes. Table
1 shows an example of this kind of strategies.
FEMA356 (2000) suggests a more general
definition as in Table 2 for rehabilitation objec-
tives. Here, we call it performance objectives.
According to FEMA356, the basic safety
objective (BSO) for an ordinary building is to
satisfy the K+P criteria. i.e., every building has
to be safe enough to satisfy LS criteria under an
earthquake with the probability of 10% per fifty
years, and withstand the earthquake with the
probability of 2% per fifty years with CP condi-
tion. Any design that satisfies either of M, N or
O alone, or satisfies any of A, E, I, B, F, and J in
addition to K+P, is considered to have enhanced
performance objective. Reversely, if a design does
not meet K or P criteria is designated as limited
performance objective. A design that uses a
lower seismic hazard or lower target Building
Performance Level than the BSO may be called
a reduced performance design.
To design a structure for specified performance
level, the design engineer needs to know the target
displacement; i.e., the extent of deformations that
A. Operational (OP), which is the level of per-
formance in which no damage is accepted for
the structure, and it behaves elastically under
service loads, minor wind, and earthquake
effects.
B. Immediate Occupancy (IO), that is the
level of performance in which little damage
may occur in the structure, and it is safe to
be reoccupied immediately following the
earthquake.
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