Page 457 - Advanced Design Examples of Seismic Retrofit of Structures

Examples of Nonengineered Buildings Chapter 6 403

FIG. 6.8 Poor bonding of a brick masonry wall. (Photo taken by Mohammad Yekrangnia.)

earthquakes, may isolate a wall section, causing it to act as a freestanding wall;
other walls may be leaning, affecting their stability. Water damage is perhaps
the most important existing condition that affects the performance of an adobe
building: it can alter the strength of adobe to such an extent that a wall may be
unable to support its own weight.
The integrity of the adobe blocks also influences seismic performance of
adobe buildings. Masonry integrity is a function of the bonding pattern and
the cohesion between the adobe blocks and mortar. When there is poor bonding
(Fig. 6.8), the walls may not behave monolithically as well-constructed adobe
walls typically do.
In addition, the effects of preexisting conditions in terms of moisture and
unrepaired cracks can have profound effects on seismic response of adobe
buildings. Moisture rising from the base of adobe walls can drastically reduce
the compressive and shear strength of adobe material. Also, the previously-
initiated and developed cracks and generally any form of structural damage
can have a moderate to high negative influence on the performance of adobe
buildings during earthquakes.
The summary of the field observation of the extent of damage to adobe
buildings after the Northridge earthquake is shown in Fig. 6.9. In this figure,
the qualitative damage states proposed by Earthquake Engineering Research
Institute (EERI) presented in Table 6.2 were used for determination of damage
severity to the surveyed adobe buildings. Nonetheless, the more detailed dam-
age classification by post-earthquake rapid assessment can be found in ATC
20 [28], AeDES [29], and other related documents.

6.4.1.4 Experimental Studies
In order to understand better the common vulnerability of adobe houses and the
effectiveness of different retrofit measure on the seismic performance