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DOE-STD-1020-2002
demand and the resulting total demand is compared to the capacity determined from
member forces at ultimate/limit-state stress level to determine structural adequacy.
The spectral reduction factors and inelastic energy absorption factors are evaluated
based upon the permissible inelastic behavior level, which depends on the materials and type of
construction. For ductile steel moment frames, relatively large reduction factors or inelastic
energy absorption factors are used. For less ductile shear walls or braced frames, lower
reduction values or inelastic energy absorption factors are employed. For more hazardous
facilities, lower reduction factors or inelastic energy absorption factors may be used to add
conservatism to the design or evaluation process, such that increased probability of surviving any
given earthquake motion may be achieved.
The inelastic energy absorption factor approach is employed for design or evaluation of
Performance Category 3 and higher SSCs by these criteria. This approach is recommended in
the DOD manual for seismic design of essential buildings (Ref. C-5). Inelastic energy
absorption factors are called F in these criteria. Inelastic energy absorption factors have the
advantage over spectral reduction factors in that different values may be specified for individual
elements of the facility instead of a single spectral reduction factor for the entire lateral force
resisting system. As a result, critical elements such as columns or connections can be easily
designed for larger forces by specifying a smaller inelastic energy absorption factor than for
other elements.
Base shear reduction coefficients that account for energy absorption due to inelastic
behavior and other factors are called R by the IBC provisions. R is more like a spectral
reduction factor in that it is applied to the entire lateral force resisting system. There are special
IBC provisions which require critical elements such as columns or connections to be designed
for larger loads than those corresponding to the base shear equation using R. The IBC
provisions are followed for Performance Category 2 and lower SSCs by these criteria.
Reduction coefficients, R, to be used for evaluation of PC-1 and PC-2 are as per IBC
2000. Recommended inelastic energy absorption factors, F, for PC-3 and PC-4 SSCs are
presented in Chapter 2 for various structural systems. The F factors presented in Chapter 2
were established to approximately meet the performance goals for structural behavior of the
SSCs as defined in Chapter 2 and as discussed in Section C.2. These factors are based both on
values given in Reference C-5 and on values calculated from code reduction coefficients in a
manner based on the performance goals. Reference C-20 describes the detailed method for
establishing the values of F.
The response modification factor coefficients, R, by the IBC approach and inelastic
energy absorption factors, F, by the DOD approach differ in the procedures that define
permissible inelastic response under extreme earthquake loading. By the IBC approach, only the
element forces due to earthquake loads are reduced by the reduction coefficient, R, in evaluating
demand; while by the DOD approach, element forces due to both earthquake and dead and live
loads are reduced by the inelastic energy absorption factor, in evaluating demand. The effect of
this difference is that the DOD approach may be less conservative for beam or brace members
C-30


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