Page 61 - Jabalpur_EQ

Chapter 3 Brick Masonry & Relnforced Concrete Buildings

In-Plane Shear Strength of Walls
Large openings can seriously undermine the in-plane shear strength of masonry
walls. The shear capacity of masonry piers may not be enough to resist lateral
loads imposed by seismic forces. Poor in-plane shear performance was noted
with many URM structures all around the quake affected area. Diagonal shear
Cracking of masonry piers were common sight, however, in a few cases flexural
(rocking) behaviour of slender masonry piers was also noticed. Frequent in-plane
failures of the nonbearing brick infills in concrete frames was apparently due to
the reduced mortar shear capacity for the lack of overburden and the increased
stiffness of the infills. Performance of brick infilled RC frames will be discussed
later in this chapter. In the following sections, a few notable in-plane shear fail-
ures in the regions of greater shaking are discussed.

Food Sciences Building, Agriculture University
Three similar workshop units of Food Sciences Building illustrate the progression
of failure of masonry piers whose in-plane shear strengths were not adequate.
The workshop units were rectangular in plan and the front wall was about 6 m
tall and 8 m wide of which 70% was open for windows and a rolling shutter as
shown in Fig. 3-11. As a result only a small portion of masonry piers was left to
support the wall and roof above and provided the needed lateral strength. Since
the slender masonry piers were heavily loaded, they failed in the shear mode

Figure 3-11. Shear cracking of masonry piers in one workshop unit of the Food
Science Building, Agriculture University. Slender masonry piers are only mem-
bers to provide shear resistance in that plane.

Jabalpur Earthquake of May 22, 1997 51