Page 56 - Advanced Design Examples of Seismic Retrofit of Structures

48 Advanced Design Examples of Seismic Retrofit of Structures

Geometrical
Based on Code 360, when dimensions of a story are larger than 130% of its adja-
cent stories, the building is considered irregular in geometry [10]. The example
building satisfies Code 360 regulation in this regard, and hence is regular in
geometry.

Mass
According to Code 360, the total mass of each story should be within 50% dif-
ference with that of its adjacent buildings; otherwise, the building is deemed to
be irregular in mass [10]. For the example building, the total masses of the first
and second stories are 1055 ton and 836 ton, respectively. Consequently, this
building is regular in mass.

Disconnection of Load-Bearing Elements
Sometimes there is discontinuity in the lateral load-bearing system in height of
the building. This condition, which is classified by Code 360 as an irregularity,
results in an overturning effect on beams, diagrams, columns, and shear walls
[10]. For the studied building in this example, there is no discontinuity in cor-
responding walls of the stories, and hence the building is regular.

In Strength (Weak Story)
The sum of the shear strengths of the seismic-force-resisting system in any story
in each direction shall not be <80% of the strength in the adjacent story above
[2, 10]. According to Section 5.4.2.1 of ASCE 41-13, for checking the weak
story irregularity, an analysis of the entire structure shall be performed in accor-
dance with Section 5.2.4 of that document. The demand-capacity ratio (DCR)
shall be evaluated in accordance with Section 7.3.1.1 of that document for all
elements of the seismic-force-resisting system in the noncompliant stories. The
building is deemed compliant with this statement if the maximum DCR is less
than two in the stories found noncompliant in the Tier 1 screening procedure.
Based on stories’ total strength presented in Table 2.5, the building under study
is regular.

TABLE 2.5 Total Strength and Stiffness of Stories
Minimum Total Strength (MN) Total Stiffness (MN/m)
Story X-Direction Y-Direction X-Direction Y-Direction
0 4.16 (+159%) 2.27 (+145%) 7609 (+220%) 8189 (+185%)
1 2.62 1.56 3456 4426