Page 365 - Advanced Design Examples of Seismic Retrofit of Structures

338 Advanced Design Examples of Seismic Retrofit of Structures

have to be tied with BOX100 100mm. In addition, the vulnerable braces in the
sports building have to be replaced by the newly designed profiles. There are
eight beams which have to be added to the sports building to form the load trans-
fer route from the diaphragm to the foundation. The results of the evaluation
indicate there is no need to add piles to the foundations. However, the founda-
tion under the columns adjacent to the braces needs to be retrofitted. The col-
umns of the building adjacent to the braces need to be retrofitted, but other
columns of the building are not vulnerable because they have no contribution
to lateral load-bearing. The location of the added concentric braces is shown in
Fig. 5.21. The designed profiles of the concentric braces are presented in
Table 5.24. As an example, the results of the evaluation of the buildings in terms
of DCR of the structural members in the retrofitted model by concentric braces
are shown in Fig. 5.22.
Based on the geotechnical studies, the allowable soil pressures for the exam-
ple buildings are determined based on the relations below. For the pad founda-
tion and strip footing with depths of 60 and 75cm, respectively, the allowable
soil pressures for various foundation widths are listed in Table 5.25.
q a ¼12.34+4.71D+1.65B For pad foundation (main building)
q a ¼9.49+4.71D+2.07B Forstrip footing (sports building)
where B ¼foundation width and D ¼foundation depth.
Soil pressure in the retrofitted main building by concentric braces under crit-
ical load combinations is shown in Fig 5.23. As can be seen, in some
100cm 100cm foundations, the soil pressure is higher than the allowable soil
pressure according to Table 5.25. Also, some foundation of the main building is
vulnerable against punching shear, as shown in Fig 5.24. The required rein-
forcement in the retrofitted main building by concentric braces, which are
shown in Fig 5.25, is also higher than the existing reinforcement in those foun-
dations, hence indicating the need for retrofit.
Soil pressure in the retrofitted sports building by concentric braces under
critical load combinations is shown in Fig. 5.26. As can be seen, the soil pres-
sure is not higher than the allowable soil pressure according to Table 5.25. The
foundation of the sports building is adequate against punching shear as shown in
Fig. 5.27. The required reinforcement in the retrofitted sports building by con-
centric braces which are shown in Fig. 5.28 is not higher than the existing rein-
forcement in the foundation. As a result, the foundation in the sports building is
not vulnerable.

5.10.2 Eccentric Braces
Compared to concentric braces with the behavior factor of 5.5, the behavior fac-
tor of the frame buildings with eccentric braces is 7.0, which leads to 27%
reduction on the design seismic loads, according to Standard 2800 [2]. How-
ever, as stated in Section 5.9.3.2, there is a need to add new beams to the build-
ings to resist the considerable forces from the braces. The results of the analyses