Page 55 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Two-Story Unreinforced Masonry Building Chapter 2 47

4 4
3 3
2 2
1 1
(A) (B)
FIG. 2.30 The effects of a diaphragm’s rigidity on walls deformations. (A) Rigid diaphragm.
(B) Flexible diaphragm.

diaphragm’s stiffness which is >50% of that in the adjacent floors, the dia-
phragm is deemed to be irregular [10]. All the diaphragms are regular in the
studied building in this chapter.

Out-of-Plane
Based on Code 360, when one of the lateral load-bearing components in a story
is misaligned compared to other adjacent components, the building is deemed to
be irregular [10]. An example of this type of irregularity is when for some rea-
son, for example, architectural limitation, a masonry wall is placed eccentric
with respect to the axis on which other walls are placed. In the present example
building, there is no such condition and all the walls are aligned in several axes
to complete that particular line of resistance.

Nonparallel
Sometimes, the lateral load-bearing components of the buildings are aligned in
way that none of the building’s main directions is alongside those components.
In this case, the building is considered irregular by Code 360 because of the
existence of “nonparallel” load-bearing components [10].

2.5.4.2 In Height (Vertical)
There are numerous cases in which vertical irregularities of buildings resulted in
major problems. While the horizontal irregularities can pose extra seismic
demands on some structural components, mainly because of excessive torsions
in the stories, the vertical irregularities can cause more severe dangers, for
example, collapse that is directly attributed to the building’s gravitational load
path. All vertical elements in the seismic-force-resisting system should be con-
tinuous with the foundation. Vertical irregularity, that is, a discontinuity of
strength, stiffness, geometry, or mass in one story with respect to adjacent
stories should be avoided [2].