Page 156 - Advanced Design Examples of Seismic Retrofit of Structures

148 Advanced Design Examples of Seismic Retrofit of Structures

extended to the highest story. In stories where there is a setback in the dia-
phragm, the 80 60cm RC beams should be used in order to keep the DCR
of the northern shear wall as 3.5 (compared to that of 2.5 in the first retrofit strat-
egy). If the shear wall does not extend to the upper stories, the DCR of the north-
ern shear wall increases to 5.5. Consequently, this strategy is unacceptable.
The general schematic view of the third retrofit strategy is shown in
Fig. 3.19.

3.4.4 Scoring the First and the Second Retrofit Strategies
In order to compare the first and the second retrofit strategies, the analytic hier-
archy process (AHP) [2] scoring table is presented in Table 3.8. The first strat-
egy has a higher score and hence is selected as the retrofit strategy for this
project.

3.5 DETAILED DESIGN OF THE SELECTED RETROFIT
METHOD (PHASE-2, STAGE-2)
As previously mentioned, the used analysis method is the linear dynamic one,
which is performed for two earthquake levels: Earthquake-1 and Earthquake-2,
for which the target performance levels are LS and CP, respectively. In the
models, all columns and shear wall P 2 are considered as secondary members.
Other walls (P 1 ,P 1L ,P 3 ,P 3T ,P 4 ,P 5 ,P 6, P 8 ) and other structural members are
considered as primary members. There are a total of 40 modes which are con-
sidered to take at least 90% of the dynamic mass of the building into account [3].
Two main tasks are considered in the selected retrofit strategies: proper connec-
tion of the northern and southern building parts; and modification of the shear
walls aspect ratio, arrangements, retrofit, and adding new shear walls in both
directions. It is noteworthy that selection of the location of the shear walls is
based on minimizing the torsion and more balanced distribution of the seismic
demands between the structural members. In addition, architectural, feasibility,
and economical considerations play a role in this selection.
One idea in the retrofit design is to divide the existing shear walls P1 and P4
with the dominant shear behavior (due to their geometrical characteristics) in
order to alter it to flexural behavior. To do this, the shear wall P 4 is demolished
in the length of 2.5m from the West in all stories. The remaining part of this wall
is divided into two separate parts by cutting through the wall with a 20-cm width
vertical groove. This creates the two new walls P 4 and P 8 in the plan of the retro-
fitted building. Moreover, the shear wall P 1 is divided into two P 1L and P 1 ,
and two flanges are also added to each new wall as shown in Fig. 3.20. Some
views of the process of demolition and dividing these shear walls are shown in
Figs. 3.21 and 3.22.