A system overstrength factor, So, provided in Table
QE = the effect of horizontal seismic forces
7-1 is intended to quantify the actual force that can be
delivered to sensitive individual brittle elements, the
failure of which could result in the loss of a complete
lateral-force-resisting system or in instability or
collapse. The factor is similar in application to the
D = the effect of dead load.
3Rw/8 factor prescribed in the UBC, and represents an
estimate of the combined design, material, and
Special Combination of Loads.
system overstrengths that could effect a brittle or
specifically required by FEMA 302, or when in the
judgement of the designer the effects of structural
overstrength need to be considered, the design
Combination of Load Effects.
components shall be defined by the following
E = S oQE + 0.2SDS D
1.2D + 1.0E + 0.5L + 0.2S
E = S oQE - 0.2SDS D
or 0.9D + 1.0E
Where E, QE, SDS and D are as defined in Paragraph a
above, and S o is the system overstrength factor
where: D,E,L, and S, are respectively, dead,
defined in Paragraph 4-5 and listed in Table 7-1.
earthquake, live, and snow loads.
Example applications for Equations 4-6 and 4-7
include the design of columns under discontinuous
The effect of the earthquake load, E, is defined by:
shear walls or braced frames, and the design of frame
members in braced frames effected by overstrength in
E = DQE + 0.2SDSD
or E = DQE - 0.2SDSD
Three structural performance levels, as described in
E = the effect of horizontal and vertical
Table 4-3, are considered to be acceptable by this
document. Performance Level 1 (Life Safety) is the
minimum performance level required of all Seismic