Page 346 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building Retrofitted Chapter 5 325

5.8.5 Braces
Brace actions are classified as deformation-controlled actions which are eval-
uated based on Eqs. (5.32) and (5.33) for braces in compression and tension,
respectively. The results of the control of the braces in the sports building in
the linear static method are presented in Table 5.21. Plastic hinges formation
in the braces in the sports building under PX1 shown in Fig. 5.14. The results
of the nonlinear analysis on the sports building is presented in Table 5.22.
P CE CðÞ ¼ 1:7 F as A
0 1
1
B C (5.32)
ð F as ¼ B:F a Þ, B ¼ C
λ
B
@ A
1+
2C c
s ffiffiffiffiffiffiffiffiffiffi
2
2π E
C c ¼
F y
(5.33)
P CE TðÞ ¼ A:F ye
where:
P CE(C) ¼expected strength of the brace in compression;
P CE(T) ¼expected strength of the brace in tension;
F as ¼allowable compressive stress in braces; and
B¼coefficient for reduction in stress.
We have
1:0 692
λ ¼ ¼ 284:77
2:43
6025
ffiffiffiffiffiffiffi ! 284 > 124:04
λ < p
F ye
1
¼ 0:482
284:77
B ¼
1+
265:2
105 10 5 kg
F a ¼ ¼ 129:47
2 2
ð 284:77Þ cm

kg
F as ¼ F a B ¼ 129:47 0:482 ¼ 62:4
cm 2
5.8.6 Foundation
Based on ASCE 41 [3], prescriptive expected capacities shall be used where
construction documents or previous geotechnical reports for the existing build-
ing are available and provide information on foundation soil design parameters.