analytical procedures, as described in subsequent
paragraphs for enhanced performance objectives,
may be necessary or desirable for highly irregular or
complex structural systems.
Design Coefficients and Factors for Basic
This chapter prescribes the acceptance criteria for
Seismic-Force Resisting Systems. Table 7-1 (Table
the various performance objectives described in
5.2.2 of FEMA 302) lists the basic seismic-force-
Chapter 4. The applicable acceptance criteria for
resisting systems, and for each system, provides
each performance objective are provided for each of
the analytical procedures described in Chapter 5.
modification factor, R; the systems overstrength
Numerical values of the criteria for specific
factor, So; the deflection amplification factor, Cd;
structural systems are provided in Chapter 7.
limitations by Seismic Design Category.
Performance Objective 1A.
Deflection and Drift Limits.
This is the basic Life Safety
(Table 5.2.8 in FEMA 302) provides the allowable
performance objective for all buildings, and is the
story drift applicable to each performance level for
only performance objective for Seismic Use Group I
representative structural systems. The story drift, ),
buildings, which constitute the vast majority of
is computed as the difference of the deflections *x, of
military construction. The design is based on the
the center of mass at the top and bottom of the story
FEMA 302 seismic provisions with an applicable
under consideration. The story deflections are equal
Response Modification Factor, R, and drift limits
to the deflections *xe, determined from the elastic
based on elastic analysis. The designer should not
analysis multiplied by the deflection amplification
lose sight of the fact that an elastic analysis with an
capacity in the structural system, and structural
detailing that results in brittle or nonductile response
criteria for Performance Objective 1A consists in
confirming that the capacity of the structural
lead to the development of a premature failure
components and elements satisfies the combined
demand of the gravity and design loads in
accordance with the LRFD procedures referenced for
As indicated in
the various structural material in FEMA 302.
Table 4-4, the minimum analytical procedures for
Additionally, compliance with the drift and detailing
this performance objective are the linear elastic static
or dynamic procedures with ELF or modal analysis
incorporated by reference, must be met.
in accordance with FEMA 302.