Page 303 - Advanced Design Examples of Seismic Retrofit of Structures

292 Advanced Design Examples of Seismic Retrofit of Structures

S a ¼response spectrum acceleration, at the fundamental period and damp-
ing ratio of the building in the direction under consideration which is deter-
mined based Code 360 [1];
W ¼effective seismic weight of the building, including the total dead load
and applicable codified portions of other gravity loads. According to Code 360,
the dead loads also include the weight of partition walls and the total operating
weight of permanent equipment, and the live loads are 20% of the codified live
loads including snow [5]; and
C 1 ¼modification factor to relate expected maximum inelastic displace-
ments to displacements calculated for linear elastic response. This factor is
determined based on either of these methods.
(1) Based on Eq. (5.6)

25 R u 1Þ
ð
T 0:2 ! C 1 ¼ 1+
a
R u 1
0:2 < T 1 ! C 1 ¼ 1+ (5.6)
aT 2
T > 1 ! C 1 ¼ 1
where:
a ¼site class factor;
¼130 site Class A or B according to ASCE 41-13 [1];
¼90 site Class C;
¼60 site Class D, E, or F;
T ¼fundamental period of the building in the direction under consideration,
calculated in accordance with Section 1.7 of Code 360, including modification
for Soil-Structural Interaction (SSI) effects of Section 3.2.6 of this
document; and
R u ¼ratio of elastic strength demand to yield strength coefficient calculated
in accordance with Eq. (5.7). If the elastic base shear capacity substituted V e is
available, Eq. (5.8) can be used interchangeably.
DCR max
R u ¼ C m 1 (5.7)
1:5
S a
R u ¼ C m (5.8)
V e =W
where DCR max is the largest demand to capacity ratio (DCR) computed for any
primary component of a building in the direction of response under consider-
ation, taking C 1 ¼ C 2 ¼ C m ¼1.0.
(2) Based on Eq. (5.9) when R u cannot be determined.