Page 30 - Advanced Design Examples of Seismic Retrofit of Structures

22 Advanced Design Examples of Seismic Retrofit of Structures

(A) (B)

(C) (D)
FIG. 2.7 Examples of collapse of gable-end wall due to out-of-plane actions. (A) After 2005 Zar-
and earthquake. (B) After 2003 Bam earthquake. (C) After 2005 Zarand earthquake. (D) After 2003
Bam earthquake. (Permission from DRES.)
2.4.2 Mid-Height Flexural Out-of-Plane Cracks
Mid-height flexural out-of-plane cracks in URM walls are considered the sec-
ond most frequent failure mode in this direction and are activated when a wall is
constrained at the top. The mid-height flexural out-of-plane cracks can achieve
considerable extra strength due to activation of arching actions in the wall.
Examples of mid-height flexural out-of-plane cracks are presented in Fig. 2.9.

2.4.3 Damage to Surrounding Walls

There are numerous observations that indicate surrounding walls, if not prop-
erly secured at the base, cannot show acceptable seismic performance. The main
failure mode of these walls is overturning at the base. Fig. 2.10 shows examples
of collapse of surrounding walls. Similar to other types of out-of-plane damage
of URM walls, this type of damage can be regarded as brittle failure mode and
acceleration-sensitive.

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2.4.4 Collapse of Parapet Walls and Facades
Observation of the past earthquakes proves seismic vulnerability of parapet
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walls and facades even in moderate seismic actions. Although not classified