Page 62 - Advanced Design Examples of Seismic Retrofit of Structures

54 Advanced Design Examples of Seismic Retrofit of Structures

(2) In the absence of precise calculations, C 2 can be taken as 1.0.
For the example building, it was assumed that C 2 ¼1.
C m ¼effective mass factor to account for higher modal mass participa-
tion effects obtained from Table 3-4 of Code 360 [10]. C m is 1.0 for
masonry buildings which are categorized as “Other” structural systems in
this table.
Based on Standard 2800 [7], the spectral acceleration can be determined by
multiplication of the site PGA (A in Eq. 2.7) and the reflection factor (B in Eq.
2.7). In this example, it is assumed the building is located in a zone with high
seismicity and as such, the site PGA is 0.3. Also, the reflection factor for Soil
type B according to ASCE 41-13 [2] in zones with high seismicity is conserva-
tively assumed to be 2.75 which is corresponding to the apex of the design spec-
trum. As a result:
S a ¼ A B (2.7)

A ¼ 0:3g
B ¼ 2:75
S a ¼ 0:3 2:75 ¼ 0:825g

Based on the aforementioned factors, the base shear demand can be calcu-
lated as:
C 1 ¼ 1:41;

C 2 ¼ 1:00;
C m ¼ 1:00;
S a ¼ 0:825 g;
For determination of the total mass of the building, we have:

W ¼ W Wall + W Ceiling +25%W Live

W Wall ¼ W Wall 1 + W Wall 2
¼ 50% W WS1 Þ +50% W WS2 Þ
ð
ð
W Wall 1
¼ 50% 523, 861Þ +50% 570, 237Þ ¼ 547,049kg
ð
ð
W Wall 1
ð
¼ 50% W WS2 Þ
W Wall 2
¼ 50% 570, 237Þ ¼ 285,118kg
ð
W Wall 1
W Wall ¼ 547,049 + 285,118 ¼ 832,167kg
W Ceiling ¼ W Ceiling 1 + W Ceiling 2
W Ceiling ¼ 394,595 + 530,991 ¼ 925,586kg