Page 32 - Advanced Design Examples of Seismic Retrofit of Structures

24 Advanced Design Examples of Seismic Retrofit of Structures

(A) (B)

(C) (D)
FIG. 2.9 Examples of mid-height flexural out-of-plane cracks. (A) Flexural out-of-plane cracks in
a classroom. (B) Mid-height flexural out-of-plane cracks. (C) Activation of arching action in the
wall after 2005 Zarand earthquake. (D) Flexural out-of-plane cracks in a classroom. (Permission
from DRES.)
as structural damage, this kind of damage can cost lives when people are aban-
doning buildings during earthquakes.
The damage mechanism in parapet walls is due to out-of-plane failure, while
¸
in facades, in-plane and out-of-plane actions may contribute to their collapse. In
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some cases, no proper mortar has been found between the facade and the sup-
porting wall. However, mortar itself cannot suffice and guarantee stability of the
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facade; hence, connectors in the form of steel anchor bolts are necessary to sta-
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bilize the facade against seismic actions. Several examples from past earth-
quakes are presented in Figs. 2.11 and 2.12 for the collapse of parapet walls
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and of facades, respectively.
2.4.5 In-Plane Damage of Walls
In many cases, combined in-plane failure modes are observed in URM walls,
and generally, one failure mode can precipitate another. For instance, rocking
can end with toe crushing because of stress concentration at the wall’s toe. As
previously stated, these failure modes depend on various parameters including
aspect ratio (the ratio of a wall’s height to its length), mortar shear strength,
compressive strength of masonry prism, and the level of vertical loads on the
wall. Moreover, the corners of the openings are among the most vulnerable parts