Page 163 - Advanced Design Examples of Seismic Retrofit of Structures

Example of an RC Building Retrofitted by RC Shear Walls Chapter 3 155

Seismic Loads
According to Code 360, the seismic loads in the linear static procedure are
considered based on Eq. (3.1);

Q E LSP ¼ C 1 C 2 C m S a W (3.1)
where:

Q E LSP ¼pseudo lateral force in linear static procedure;
S a ¼response spectrum acceleration, at the fundamental period and damping
ratio of the building in the direction under consideration;
C 1 ¼modification factor to relate expected maximum inelastic displace-
ments to displacements calculated for linear elastic response which is based
on Eq. (3.2), which is 1.0 for the example building:
T s T
1 C 1 ¼ 1+ (3.2)
2T s 0:2
C 2 ¼modification factor to represent the effect of pinched hysteresis shape,
cyclic stiffness degradation, and strength deterioration on maximum dis-
placement response. In the absence of precise calculations, C 2 can be taken
as 1.0; and
C m ¼effective mass factor to account for higher modal mass participation
effects obtained from Table 3.4 of Code 360 [1]. C m is 0.8 for RC buildings
with at least three stories in this table.
As a result, the equivalent static load is:
Q E LSP ¼ 0:8S a W
The seismic loads in the linear dynamic procedure are considered based
on Eq. (3.3):
Q E LDP ¼ C 1 C 2 S a W (3.3)
and hence:

Q E LDP ¼ S a W ¼ ABW
According to Code 360, the natural period of the first mode of vibration for
the example building is according to:
T ¼ 0:05H 0:75 (3.4)

where:
T¼natural period of the first mode; and
H¼total height of the building.

For both the northern and southern buildings, the reflection factor (B) is 1.94
and the design acceleration (A) for the region with very high seismicity is 0.35.