earthquake resistant structure

1. ADVANCED CONSTRUCTION
TECHNOLOGY
SUNDARRAJAN P
LECTURER / CIVIL

2. UNIT III
3.2 EARTH QUAKE RESISTING CONSTRUCTION
Indian Seismicity – Earthquake History - Definition of terms used - Behavior of
structures in the past Earthquakes – Seismic forces – Effect of seismic forces on
Buildings – Planning of Earthquake resistant Buildings - Roofs and Floors
Articulation joints – Expansion Joints – I.S. code provision – Alterations to
Buildings – Foundation – Permissible increase in the allowable Bearing capacity
of soils - Seismic coefficient for different zones – Construction of framed
buildings in Earthquake zones – Walls – Beams etc.

3. Earthquake
• An earthquake is the result of a sudden release of stored energy in the
Earth's crust that creates seismic waves

5. Indian Seismicity
• Seismicity is defined as the distribution of seismic activity in time, location,
magnitude & depth during the historical & recent instrumented period.
Studies of seismicity are of great importance to understand the dynamic
behaviour of the earth and is useful to determine the earthquake hazard in a
specific region.

8. Indian earthquake history

9. Terms in earthquake
• Focus
• Epicenter
• Intensity of earthquake
• Magnitude of earthquake
• Seismograph
• Seismoscope
• Seismometer
• Seismogram
• Richter scale
• Fault
• Plates
• Seismic waves

10. Focus & Epicenter
• The focus is the place inside Earth's crust where an earthquake originates
• The point on the Earth's surface directly above the focus is the epicenter.

11. Fault & Plates
• Fault: A fracture in the rocks that make up the Earth’s crust
• Plates: Massive rocks that make up the outer layer of the Earth’s surface and
whose movement along faults triggers earthquakes

12. Intensity & Magnitude
• Magnitude is a measure of earthquake size and remains
unchanged with distance from the earthquake
• Intensity describes the degree of shaking caused by
an earthquake at a given place and decreases with distance from
the earthquake epicentre Or
• describing the severity of an earthquake in terms of its effects on
the earth's surface.

14. Seismograph & Seismoscope
• seismograph is an instrument that automatically detects and
records the intensity, direction and duration of earthquakes and
similar events
• seismoscope is an instrument that indicates the occurrence of an
earthquake.

15. Seismometer & Seismogram
•
•

18. Richter scale
• he Richter magnitude scale is a scale of numbers used to tell the power
(or magnitude) of earthquakes.
• . A Richter scale is normally numbered 1-10, though there is no upper limit.
• It is logarithmic which means, for example, that an earthquake measuring
magnitude 5 is ten times more powerful than an earthquake measuring 4.
• Earthquakes measuring 1-2 on the scale happen regularly, and they are so small
that people cannot feel them.
• Earthquakes measuring upwards of 7 are less frequent but very powerful, and
can cause a lot of destruction.

20. Seismic wave
• Seismic waves are waves of energy that travel through the Earth's
layers, and are a result of earthquakes, volcanic eruptions, magma
movement, large landslides and large man-made explosions that
give out low-frequency acoustic energy

22. Behavior of structure in the past earthquakes
• Buildings are fixed to the ground
• As the base of a building moves the superstructure including its contents tends to
shake and vibrate from the position of rest, in a very irregular manner due to the
inertia of the masses.
• When the base of the building suddenly moves to the right, the building moves to
the left relative the base as if it was being pushed to the left by an unseen force
which we call Inertia Force.
• Actually, there is no push at all but, because of its mass, the building resists any
motion. The process is much more complex because the ground moves
simultaneously in three mutually perpendicular directions during an earthquake

24. Seismic force
• Consist of various forms of waves originating at center of disturbance and causing
horizontal & vertical ground movements or vibrations
• They are complicated
• Horizontal vibrations are much greater than vertical ones
• They are mainly considered in designing earthquake resisting structures
• Severe earthquake always leaves in its way may collapsed buildings and much structural
damage
• Properly designed structure is capable of withstanding the strongest recorded earthquake
• Practically true in small buildings with very little extra cost

25. Effects of seismic forces on buildings
• Most destructive force caused by horizontal earth motion
• When ground below the structure is moved suddenly one side the building will try
to remain in its original position because of its inertia
• Earthquake occur in any direction hence building should be strong enough to resist
lateral forces in any direction
• Bottom part move with ground and tendency to transmit the motion to the
building above
• Sudden change from rest to motion causes forces on superstructure in a direction
opposite to that of earth movement

26. Provision of earthquake design
• Ridge and valley effects in buildings as earthquake produce movements in form of
waves
• Every building has natural period of vibration when vibrations are introduced in a
building by earthquake, A resonance would occur and building would be completely
destroyed
• Rate of vibration during earthquake 1 to 2.5 sec
• Self vibration of R.C building 0.3 to 0.5 sec for building height upto 27.50m
• For grater heights vibrations are equal to earthquakes vibration

27. Provision of earthquake design
• All components of building should be firmly tied together and so stiffly braced that
the building would tend to move as a unit
• Floors and cross walls should be continuous thought the building and openings
should be avoided near the outside corners
• Different parts of the same building dissimilar in mass of stiffness should be
separated by space sufficient to prevent them from pounding one another
• Articulation joints providing
• Fire proof building construction

28. Planning of earthquake resistant buildings
• Length of building should not be more than three times of its width
• Longer buildings are constructed by dividing into separate structures by articulation joints
• Light as well as strength and comfort
• Center of gravity of building should be kept as low as possible
• Parapet walls, cornices, ornamental features should be avoided. If used they are firmly tied
• Internal partition wall should meet at a common vertical point
• Continuous plane of weakness should be avoided by staggering openings

29. Roof trusses
• All trusses should be sufficiently anchored to concreter bed or frame
• Slotted plates are fixed at one end of truss for temperature changes
Roof slabs
• Rest on concrete bed without any direct tie
• Provided slab is prevented by offsets in slab fitting over the concrete bed

30. • Wooden plates and joists
• No plates should be sunk into masonry walls
• They should be placed on top of wall or projection in concrete bed or beam and fixed
rigidly
• Ground floors
• Not attached to main structures
• Ceilings
• Plaster should not applied exceeding 3mm

31. Articulation joint
• Provided to deal with lack of symmetry in buildings
• It is a sufficient space provided to prevent different parts of building
dissimilar in stiffness from providing another during on earthquake

32. Expansion joint
• Joints provided in roof slabs to full depth to prevent local cracking due to
temperature

34. Alteration to buildings
• Increase lateral strength and stiffness
• Increase ductility
• Increase integral action and continuity of member
• Eliminate effects of irregularities
• Ensure adequate stability against overturning and sliding

35. Foundations
• Preferably avoid differential settlement
• Avoid foundation in loose soil, fine sand, black cotton soil and clays
• All induvial footing in soft soil shall be connected by R.C.C ties atleast in two
direction
• Make plinth protection around the house wide enough with drain to prevent
water going under footings

36. permissible increase in the allowable bearing
capacity of soil

37. Seismic coefficient for different zones
• he Seismic Coefficients are dimensionless coefficients which represent
the (maximum) earthquake acceleration as a fraction of the acceleration
due to gravity.
Zone no. Seismic coefficient
V 0.08
IV 0.05
III 0.04
II 0.02
I 0.01

38. • For underground structure and foundations at 30m depth or beloe – 0.5xo
• 30m depth above – between xo and 0.5xo