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DOE-STD-1020-2002
heavily loaded by dead and live loads. As a result, the criteria presented in this document utilize
F in a manner more similar to the IBC in that only the elastically computed seismic response is
reduced. This approach is more consistent with common seismic design/evaluation practice.
In addition, the approach for permitting inelastic behavior in columns subjected to both
axial forces and bending moments differs between the IBC and DOD provisions. By the IBC
approach, seismic axial forces and moments are both reduced by R, and then combined with
forces and moments due to dead and live loads, along with an appropriate load factor. The
resultant forces and moments are then checked in code-type interaction formulas to assess the
adequacy of the column. By the DOD approach, column interaction formulas have been
rewritten to incorporate the inelastic energy absorption factor (as shown in Figures 3-2 and 3-3
of Reference C-5). By the DOD interaction formulas, the inelastic energy absorption factor is
applied only to the bending moment, and axial forces are unaffected. In addition, the inelastic
energy absorption factors are low compared to ratios for other types of members such as beams.
The DOD approach for columns is followed by these guidelines for PC-3 and PC-4 SSCs.
PC-3 and PC-4 SSCs can be evaluated by elastic dynamic analyses. However, limited
inelastic behavior is permitted by utilizing inelastic energy absorption factors, F. The inelastic
energy absorption factor, F is related to the amount of inelastic deformation that is permissible
for each type of structural element. Less inelastic behavior is permitted in less ductile elements
such as columns or masonry walls than in very ductile beams of specially detailed moment
frames. In addition, by permitting less inelastic behavior for PC-3 and PC-4 as compared to the
larger R factors for PC-1 and PC-2, the margin of safety for that category is effectively increased
(i.e., the risk reduction ratio, RR, is increased), and the probability of damage is reduced in
accordance with the performance goals. Note that the F values are employed with acceptance
criteria based on ultimate stress limits with unity load factors while the R values are employed
with acceptance criteria based on either ultimate stress limits compared with response including
load factors or allowable stress limits.
The inelastic energy absorption factor is defined as the amount that the elastic-computed
seismic demand may exceed the capacity of a component without impairing the performance of
the component. Thus, the elastic-computed seismic demand DS may be divided by an inelastic
energy absorption factor F to obtain an inelastic seismic demand DSI. This inelastic energy
absorption factor F should be defined by:
F = F
5%
(C-7)
where F5% is the estimated inelastic energy absorption factor associated with a permissible level
of inelastic distortions specified at about the 5% failure probability level.
If practical, it would be preferable to perform nonlinear analysis on the structure or
component being evaluated in order to estimate F5% for use in Equation C-7 to define F.
C-31


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