Page 70 - Jabalpur_EQ

Brick Masonry & Reiforced Concrete Buildings
Chapter 3

Figure 3-24. Shear and flexural cracking of infill wall, College of Agriculture
building, Agriculture University.

PERFORMANCE OF INFILL WALLS

Unreinforced brick infill walls crack at relatively small deformations in a rather
brittle manner, and they also suffer from flexure failures if their slenderness
(height to thickness ratio) is large. Fig. 3-24 shows the typical damage that was
observed in many infill walls. The wall was subjected to shear as well flexure
forces resulting in a combination of diagonal shear as well as horizontal flexure
cracks. The masonry infill walls increased the lateral strength of weak RC frames
when the integrity of RC frames under lateral loads was doubtful. Furthermore,
they provided a redundant load path to carry both vertical and shear forces safely
to the foundation.

Brittle failure of unreinforced masonry infills was the most common structural
damage in the affected area, and often times the severe cracking resulted in the
shedding of masonry, with great hazards to life. Infills fail by splitting due to
large orthogonal tensile stresses in the diagonalcompression strut. In addition, the
loss of infill due to out-of-plane forces is possible for the lack of anchorage or
excessive slenderness of the wall.

There are two ways to remedy these deficiencies of infills. First, infills may be iso-
lated from the frame by providing a sufficient gap to accommodate seismic defor-
mations of the frame and in providing out-of-plane support to masonry infills. It
should be noted that the frame alone may be deficient in lateral strength, stiffness

Jabalpur Earthquake of May 22, 1997 60