Page 308 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building Retrofitted Chapter 5 297

(1) Where the effects or actions of gravity loads and seismic forces are addi-
tive, the action caused by gravity loads, Q G , shall be obtained in accordance
with Eq. (5.15):
Q G ¼ 1:1 Q D + Q L + Q s Þ (5.15)
ð
where:
Q D ¼action caused by dead loads;
Q L ¼action caused by live load, equal to 25% of the unreduced live load
obtained in accordance with ASCE 7 [6] but not less than the actual live
load; and
Q s ¼action caused by effective snow load which is assumed to be zero in
this example; and
Q UD ¼deformation-controlled action caused by gravity loads and earth-
quake forces.
(2) Where the effects or actions of gravity loads and seismic forces are coun-
teracting, the action caused by gravity loads, Q G , shall be obtained in accor-
dance with Eq. (5.16):

Q G ¼ 0:9Q D (5.16)

5.5.5.2 Force-Controlled

According to Code 360, force-controlled actions for the LSP denoted as Q UF
shall be calculated using one of the following methods:
(1) Q UF shall be taken as the maximum action that can be developed in a
component based on a limit-state analysis considering the expected strength
of the components delivering force to the component under consideration, or
the maximum action developed in the component as limited by the nonlinear
response of the building.
(2) Alternatively, Q UF shall be calculated in accordance with Eq. (5.17).
Q E
Q UF ¼ Q G (5.17)
C 1 C 2 J
where:
Q UF ¼force-controlled action caused by gravity loads in combination with
earthquake forces; and
J ¼force-delivery reduction factor, greater than or equal to 1.0, taken as the
smallest DCR of the components in the load path delivering force to the com-
ponent in question. Alternatively, values of J equal to 2.0 for a high level of
seismicity, 1.5 for a moderate level of seismicity, and 1.0 for a low level of seis-
micity shall be permitted where not based on calculated DCRs. In any case
where the forces contributing to Q UF are delivered by components of the
seismic-force-resisting system that remain elastic, J shall be taken as 1.0.