Page 456 - Advanced Design Examples of Seismic Retrofit of Structures

402 Advanced Design Examples of Seismic Retrofit of Structures

Vertical corner crack
Cross cracks at corners

Local section instability Horizontal upper-wall crack

Damage at openings
Diagonal corner crack

Gable-end wall collapse

Damage at intersection of
perpendicular walls
FIG. 6.7 Typical failure typologies observed in historic adobe buildings after the Northridge
earthquake [27]. (Permission from Getty Adobe.)
(b) the geometrical characteristics of the structure, that is, the configuration of
the adobe walls, roof, floors, openings, and foundation; (c) the existence and
effectiveness of seismic retrofit measures; and (d) the condition of the building
at the time of the earthquake [26].
Geometry plays an important role in determination of seismic response of
adobe buildings. For example, thin adobe walls with a high slenderness
(height-to-thickness) ratio will perform differently than a thick wall with a small
slenderness ratio. A freestanding adobe wall will show different response char-
acteristics compared to that in a wall buttressed by perpendicular walls. The
existence of openings greatly changes the adobe walls failure patterns compared
to that in a corresponding solid wall.
In many cases, previously installed seismic retrofit measures have a positive
effect on the seismic performance of an adobe building. Bond beams, buttresses,
tie-rods, and other structural elements that add resilience and/or continuity to a
structural system are beneficial. Roof and mid-height flooring/ceiling systems
can significantly affect the overall performance. Good connections between
adobe walls and the roof and floor can greatly improve the seismic performance
by providing integrity. Negative effects can also result from seismic retrofit mea-
sures by creating stress concentrations leading to other types of damage [26].
The condition of a building at the time of an earthquake plays a significant
role in its performance. Preexisting cracks, perhaps resulting from previous