Page 236 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building With Masonry Infill Walls Chapter 4 229

1.2

1
Spectral acceleration, g 0.6
0.8

0.4

0.2

0
0 0.5 1 1.5 2 2.5
Natural period, s
FIG. 4.14 Design spectral acceleration on soil type III with very high seismicity.

(1) Based on Eq. (4.18).

25 R u 1Þ
ð
T 0:2 ! C 1 ¼ 1+
a
R u 1 (4.18)
0:2 < T 1 ! C 1 ¼ 1+
aT 2
T > 1 ! C 1 ¼ 1
where:
a¼site class factor:
¼130 site Class A or B according to ASCE 41 [1];
¼90 site Class C according to ASCE 41;
¼60 site Class D, E, or F according to ASCE 41;
T¼fundamental period of the building in the direction under consideration,
calculated in Section “Natural Period of the Building”; and
R u ¼ratio of elastic strength demand to yield strength coefficient calculated
in accordance with (4.19). If the elastic base shear capacity substituted V e is
available, Eq. (4.20) can be used interchangeably.

DCR max
R u ¼ C m 1 (4.19)
1:5
S a
R u ¼ C m (4.20)
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 ¼C 2 ¼C m ¼1.0.