Page 11 - EQTips_Eng

IITK-BMTPC Earthquake Tip 5

What are the Seismic Effects on Structures? page 2
have been observed in many earthquakes in the past
Z (e.g., Figure 5a). Similarly, poorly designed and
constructed reinforced concrete columns can be
Y disastrous. The failure of the ground storey columns
resulted in numerous building collapses during the
X 2001 Bhuj (India) earthquake (Figure 5b).

Figure 3: Principal directions of a building

However, horizontal shaking along X and Y
directions (both + and – directions of each) remains a
concern. Structures designed for gravity loads, in
general, may not be able to safely sustain the effects of
horizontal earthquake shaking. Hence, it is necessary
to ensure adequacy of the structures against horizontal
earthquake effects.
Flow of Inertia Forces to Foundations
Under horizontal shaking of the ground,
horizontal inertia forces are generated at level of the (a) Partial collapse of stone masonry walls

mass of the structure (usually situated at the floor during 1991 Uttarkashi (India) earthquake

levels). These lateral inertia forces are transferred by
the floor slab to the walls or columns, to the
foundations, and finally to the soil system underneath
(Figure 4). So, each of these structural elements (floor
slabs, walls, columns, and foundations) and the
connections between them must be designed to safely
transfer these inertia forces through them.

Inertia Forces

Floor Slab
(b) Collapse of reinforced concrete columns (and

Walls building) during 2001 Bhuj (India) earthquake

and/or Columns
Figure 5: Importance of designing walls/columns

for horizontal earthquake forces.

Foundations
Reading Material
Chopra,A.K., (1980), Dynamics of Structures - A Primer, EERI
Monograph, Earthquake Engineering Research Institute, USA
Soil
Authored by:
C.V.R.Murty
Earthquake Shaking
Indian Institute of Technology Kanpur
Figure 4: Flow of seismic inertia forces through Kanpur, India

all structural components. Sponsored by:

Building Materials and Technology Promotion
Walls or columns are the most critical elements in Council, New Delhi, India
transferring the inertia forces. But, in traditional
construction, floor slabs and beams receive more care This release is a property of IIT Kanpur and BMTPC New
and attention during design and construction, than Delhi. It may be reproduced without changing its contents
and with due acknowledgement. Suggestions/comments
walls and columns. Walls are relatively thin and often may be sent to: nicee@iitk.ac.in. Visit www.nicee.org or
made of brittle material like masonry. They are poor in www.bmtpc.org, to see previous IITK-BMTPC Earthquake Tips.
carrying horizontal earthquake inertia forces along the
direction of their thickness. Failures of masonry walls
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