Page 67 - Jabalpur_EQ

Chapter 3 Brick Masonry & Relnforced Concrete Bulldings

Dynamic Instability of Walls

The dynamic stability of masonry walls under out-of-plane loads depends on the
height to thickness ratio. This stability is also a function of the response of the
floors. It is well known fact that stiff mason1y walls amplify ground accelerations
and deliver a larger nmotions to the walls. The amount of amplifications depends
on the site soil conditions and on the aspect ratio of the wall. Most of serious fail-
ures due to this deficiency occurred in the stair case portions of buildings, which
is dealt separately later in this chapter.

Figure 3-21 shows a out-of-plane failure of wall in the top storey of a housing unit
because of amplified motions. The slender wall was not anchored to the roof slab
as seen in the figure. Failure of parapet wall can be also seen. Many other such
housing units built by Madhya Pradesh Housing Board (MPHB) suffered similar
damages. Figure 3-22 shows a similar out-of-plane failure of the staircase enclo-
sure wall and jali.

Figure 3-21. Out-of-plane
failure of the top storey cornei
wall which was not anchored
to the roof slab, Housing
Board Colony.

Jabalpur Earthquake of May 22, 1997 57