Page 165 - Advanced Design Examples of Seismic Retrofit of Structures

Example of an RC Building Retrofitted by RC Shear Walls Chapter 3 157

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 ¼ deformation-controlled action caused by gravity loads and earth-
quake forces.
2) Where the effects or actions of gravity loads and seismic forces counteract
each other, the action caused by gravity loads, Q G , shall be obtained in
accordance with Eq. (3.7):
(3.7)
Q G ¼ 0:9Q D

Force-Controlled
According to Code 360, force-controlled actions for 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 com-
ponent based on a limit-state analysis, considering the expected strength
of the components delivering force to the component under examination,
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. (3.8):
Q E
Q UF ¼ Q G (3.8)
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
component in question. Alternatively, values of J equal to 3.5 for CP perfor-
mance level, 2.5 for LS performance level, and 1.0 for IO performance level
shall be permitted where not based on calculated DCRs. In this example, this
factor is assumed to be 2.5 and 3.5 for Earthquake-1 and Earthquake-2
seismic demands, respectively. As a result, we have:
Q UF ¼ Q G 0:4Q E for LS

Q UF ¼ Q G 0:286Q E for CP