Earthquake and effect in building types precaution

1. Earthquake Resistant
Buildings

2. •An earthquake is a spasm of ground shaking
caused by a sudden release of energy in the
earth's lithosphere.
•Long time ago large collection of materials
united to form the EARTH.
•Large amount of heat was generated by this
fusion.
•The heavier and the denser material sank into
the center and the lighter one rose to the top.
Introduction
Theory of plate tectonics
•Theory proposed by German scientist A.
Wegner in 1912.
•It says- earth’s crust and upper mantle are
composed of several large thin, rigid plates that
move relative to one another.
•Due to the forces acting, stresses are
accumulated inside the earth.
Mountains
Rifts

3. Types of plate boundaries
Most earthquake occurs along the boundaries of
tectonic plate (Inter-plate Earthquake), Also
occur within the plate itself (Intra-plate
Earthquake).
Occurrence of earthquake
STAGE-A:-Rocks are made of elastic
material, and so elastic energy is stored in
them during tectonic plate action
STAGE-B:-When the rocks along the weak
region reach their strength, sudden
movement takes place.
STAGE-C:-Opposite sides of the fault
suddenly slip and release the elastic strain
energy. This sudden slip causes
EARTHQUAKE.

4. Faults
In both types of earthquakes (mentioned
above), the slip generated at the fault
during earthquakes is along both vertical
and horizontal directions (called Dip Slip)
and lateral directions (called Strike Slip)
(Figure 7), with one of them dominating
sometimes.

5. How the ground shakes?
Earthquake travels as seismic waves in all directions
through the Earth’s layers.
These waves are of two types - body waves and surface
waves.
Body ways- Primary and Secondary waves.
Surface waves-Love waves &Rayleigh waves
P-waves :- extension and compression
S-waves:-oscillate at right angle
Love-waves:- similar to s-waves with no vertical
component
Rayleigh waves:- oscillate in elliptical path in the vertical
plane

6. The instrument that
measures earthquake
shaking,
a seismograph, has three
components - the sensor,
the
recorder and the timer.
The principle on which it
works
is simple and is explicitly
reflected in the early
seismograph

7. terminologies
•The point on the fault where slip starts is
the Focus or Hypocenter
• the point vertically above this on the
surface of the Earth is the Epicenter .
•The depth of focus from the epicenter,
called as Focal Depth, is an important
parameter in determining the damaging
potential of an earthquake. Most of the
damaging earthquakes have shallow focus
with focal depths less than about 70km.
• Distance from epicenter to any point of
interest is called epicentral distance.
•Magnitude – quantitative measure of
actual size of earthquake
•Intensity- quantitative measure of actual
shaking at a location.

8. Performance of ground during Earthquake
There are always before and after shocks of earthquake

9. Earthquake zones in India

10. What are the Seismic Effects on Structures?
INERTIA FORCES IN STRUCTURES
Earthquake causes shaking of
the ground. So a building
resting on it will experience
motion at its base. Since walls
or columns are flexible, the
motion of roof is different from
that of ground.
Inertia force experienced by the
roof is transferred to the ground
via columns causing forces in
the columns.
HORIZONTAL AND VERTICAL
SHAKING
Earthquake causes shaking of
ground in all directions-X,Y,Z
Structure should sustain horizontal
earthquake shaking (x and Y
direction)
Connection between the structure
components should safely
transfer inertia forces through
them

11. How Buildings Twist During Earthquakes?
Twist in buildings, called
torsion by engineers,
makes different portions at the
same floor level to
move horizontally by different
amounts. This induces
more damage in the frames and
walls on the side that
moves more (Figure 6). Many
buildings have been
severely affected by this
excessive torsional behaviour
during past earthquakes. It is
best to minimize (if not
completely avoid) this twist by
ensuring that buildings
have symmetry in plan (i.e.,
uniformly distributed
mass and uniformly placed
lateral load resisting
systems).

12. Architectural considerations
Site level considerations
• steep slopes to be avoided
• filled up soil- foundation should always rest
on firm and not on filled up soil
• raft or pile foundations have to be provided
Building level considerations
• Height
• Horizontal size
• Proportion
• Symmetry
Component level considerations

13. How Architectural Features Affect Buildings During Earthquakes?
The behaviour of a building during earthquakes depends critically on its overall shape, size and geometry.
Size of Buildings Horizontal Layout of building Vertical Layout of building
Adjacency of Buildings

14. What is the Seismic Design Philosophy for Buildings?
•Under minor but frequent shaking, the main members of the
building that carry vertical and horizontal forces should not be
damaged; however building parts that do not carry load may sustain
repairable damage.
•Under moderate but occasional shaking, the main members may
sustain repairable damage, while the other parts of the building
may be damaged such that they may even have to be replaced after
the earthquake
• Under strong but rare shaking, the main members may sustain
severe (even irreparable) damage, but the building should not
collapse.
• Earthquake resistance Design is therefore concerned about the
damage in building should be of acceptable variety

15. How to Make Buildings Ductile for Good Seismic Performance?
• For brittle material (brick and
concrete) elongation is small for
maximum force
• For ductile material (steel)
elongation is large for maximum
force
• The composite material called
reinforced steel concrete is used
to sustain compression and
tension both

16. Importance of Seismic design Codes
Good Structural Configuration: Its size, shape and
structural system carrying loads are such that they
ensure a direct and smooth flow of inertia forces to
the ground.
Lateral Strength: The maximum lateral (horizontal)
force that it can resist is such that the damage
induced in it does not result in collapse.
Adequate Stiffness: Its lateral load resisting system
is such that the earthquake-induced deformations in
it do not damage its contents under low-to
Moderate shaking.
Good Ductility: Its capacity to undergo large
deformations under severe earthquake shaking
even after yielding, is improved by favorable
design and detailing strategies.
Helps to improve behavior of structures so that they may withstand the earthquake effects without
significant loss of life
Seismic codes are unique to a particular region or country
Earthquake resistant building has four virtues in it namely:-

17. How do brick masonry houses behave during earthquakes?

20. Why are horizontal bands necessary in masonry buildings?
1993, Latur-Earthquake

21. How vertical reinforcement helps

22. HOW DO EARTHQUAKE AFFECT REINFORCED CONCRETE BUILDING?
Infill walls share the load of beam and
column until cracking under severe ground
shaking
Infill wall that is tall and long in comparison to
its thickness can fall out of plane
The thin slabs bends along with the beam in
vertical movement
Slab usually forces the beams to move
together with it.
In most building geometric distortion of slab is
negligible in horizontal plane

23. Shear walls

27. How to Reduce Earthquake Effects on Buildings?
Two basic technologies are used to protect
buildings from damaging earthquake effects.
The Base Isolation Devices
Seismic Dampers.
The idea behind base isolation is to detach (isolate)
the building from the ground in such a way that
earthquake motions are not transmitted up through
the building, or at least greatly reduced. Seismic
dampers are special devices introduced in the
building to absorb the energy provided by the
ground motion to the building.

28. Types of seismic dampers:
viscous dampers
(energy is absorbed by silicone-based fluid
passing between piston-cylinder arrangement),
friction dampers
(energy is absorbed by surfaces with friction
between them rubbing against each other
yielding dampers
(energy is absorbed by metallic components that
yield)
How to Reduce Earthquake Effects on
Buildings?

29. BHUJ
EARTHQUAKE

30. Diaphragms
(fig. 1)
Diaphragms are horizontal resistance elements,
generally floors and roofs, that transfer the lateral forces between the vertical resistance
elements (shear walls or frames). Basically, a diaphragm acts as a horizontal I-beam.
That is, the diaphragm itself acts as the web of the beam and its edges act as flanges.
(See figure 1)
Shear Walls
Shear walls are vertical walls that are designed to receive lateral forces from diaphragms and transmit them to the ground.
The forces in these walls are predominantly shear forces in which the fibers within the wall try to slide past one another.
(fig. 2)
When you build a house of cards, you design a shear wall structure, and you soon learn
that sufficient card "walls" must be placed at right angles to one another or the house
will collapse. If you were to connect your walls together with tape, it is easy to see that
the strength of this house of cards would significantly increase. This illustrates a very
important point, in which the earthquake resistance of any building is highly dependent
upon the connections joining the building's larger structural members, such as walls,
beams, columns and floor-slabs.
Shear walls, in particular, must be strong in themselves and also strongly connected to
each other and to the horizontal diaphragms. In a simple building with shear walls at
each end, ground motion enters the building and creates inertial forces that move the
floor diaphragms. This movement is resisted by the shear walls and the forces are
transmitted back down to the foundation.

31. References
1.Earthquake Tips- learning earthquake design and construction, IITK
1.National programme for capacity building of architects in earthquake
risk management, lecture notes, SPA