Page 17 - Jabalpur_EQ

Chapter 1
Introductlon

1. Greater effect on modern urban centres: The damage caused by moderate-
size, shallow earthquakes increases proportionally with the growth of
urban centers and population. This observation was once again verified in
the Jabalpur earthquake of May 22, 1997. An area of about 15 km in radius
was severely affected by the earthquake, which caused extensive damage
to residential houses and to office buildings and caused tremendous eco-
nomic loss.

2. Compliance with seismic codes: Significant damage to residential and
commercial buildings result from prevailing construction practices to meet
building needs of a rapidly growing population in urban areas, especially
at a medium to low economic level. An architecture which not only meets
the requirements of habitability but also sound earthquake-resistant
design should be emphasized and propagated. The extent of damage
would have been drastically reduced had modern earthquake-resistant
design procedures and construction practices been followed, e.g, the pro-
visions of the Indian seismic codes.
3. Emphasis on construction quality: Units built by private builders either
for government agencies or for sale in the market, have performed rather
poorly when compared to owner-built units. One major factor responsible
for this marked difference in performance is the quality of construction
and workmanship. It is general observation that contractors and private
builders cut corners for certain types of clients and jobs.
4. Emphasis on structural design:Structural design is not as exciting as out
ward appearance (i.e., "skin") defining the architecture of the structure. It
is especially true in case of buildings where designers, architects and con-
tractors hesitate to spend in sound structural design, in spite of the fact that
structural costs are marginal. It is hoped that the experience at the Jabalpur
earthquake will motivate the building industry to take a careful look espe-
cially in high seismic regions.
5. Emphasis on ductility: It should be emphasised that the earthquake-resis-
tant design derives much of its success from the provisions which ensure
inelastic deformability of structural components and energy dissipation
capacity and less from the concept of lateral load coefficients and response
spectra. Such ductility provisions specified in the IS:13920-1993 should be
followed for all RC structures
6. Brittleness of masonry infills: The widespread damage done to infill walls
calls for more in-depth study. The members, which were non-structural for
gravity loads, became very effective structurally in resisting seismic forces
in the earthquake. The brittle nature of unreinforced infills resulted in
severe diagonal shear cracking and out-of-plane instability, causing a fall
ing hazard. The cost of repairing damages to infills can be substantial.
There is an urgent need to develop techniques to increase the ductility of
unreinforced infills which can be used for retrofitting and strengthening of
already damaged walls.
7. Stair enclosure walls: Stair enclosures were observed to be extremely sus-
ceptible to damage in residential buildings which otherwise performed

Jabalpur Earthquake of May 22, 1997 7