Page 239 - Advanced Design Examples of Seismic Retrofit of Structures

232 Advanced Design Examples of Seismic Retrofit of Structures

For buildings with flexible diaphragms, each line of framing shall be indepen-
dently evaluated.
Torsional Strength. A torsional strength irregularity shall be considered to
exist in any story if the diaphragm above the story under consideration is not
flexible and, for a given direction, the ratio of the critical element DCRs for
primary elements on one side of the center of resistance of a story, to those
on the other side of the center of resistance of the story, exceeds 1.5.
In the example building, there is no in-plane or out-of-plane discontinuity.
Because of the similar number of components in the stories and their similar
section profiles, the difference of the ratio of the average shear DCR of any story
and that of an adjacent story in the same direction is less than 25%. In addition,
the building has no torsional strength irregularities.
The Fundamental Period of the Building, T, Is Greater Than or Equal to 3.5
Times T s ; The natural period of the example building is 0.346 sec according to
Section “Natural Period of the Building,” which does not exceed
3.5 0.7¼2.45 s.
The Ratio of the horizontal dimension at any story to the corresponding
dimension at an adjacent story exceeds 1.4 (excluding penthouses); There is
no major difference in the horizontal dimensions of the stories in the example
building.
The building has a torsional stiffness irregularity in any story. A torsional
stiffness irregularity exists in a story if the diaphragm above the story under con-
sideration is not flexible and the results of the analysis indicate that the drift
along any side of the structure is more than 150% of the average story drift;
As Table 4.11 shows, the example building has no torsional stiffness irregular-
ity in any story.
The building has a vertical stiffness irregularity. A vertical stiffness irreg-
ularity exists where the average drift in any story (except penthouses) is more
than 150% of that of the story above or below; According to the results pre-
sented in Table 4.11, the example building has no vertical stiffness irregularity.
The building has a non-orthogonal lateral-force-resisting system; As the
lateral-force-resisting system, the example building has concentric braces in
the longitudinal direction (which is assumed to have already been added to
the building) and the infill panels in the transverse direction.
In conclusion, the example building can be analyzed by the linear static
procedure.

4.4.2.6 Evaluation of the Building
Actions Calculations
Deformation-Controlled Based on Code 360 [10], deformation-controlled
actions for the LSP denoted by Q UD shall be calculated in accordance with
Eq. (4.26):

Q UD ¼ Q G + Q E (4.26)