Unit 4.3 Earthquake Resistant Structures
Unit 4.3 Earthquake Resistant Structures
Unit 4.3 Earthquake Resistant Structures
Department of Geology
Ravenshaw University, Cuttack
C-13 Groundwater and Engineering Geology
Recap
• Bridges and Types
• Supports and Foundations
• Engineering Geological Considerations
• Bridge failure causes and examples
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Impact After
1. 6 dead
2. Traffic in main artery disconnected
3. ~80000 people’s livelihood impacted
as they cannot travel
4. Huge insurance payouts
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Scope
• Earthquakes
• Seismic Waves
• Epicentre, Focus
• Magnitude & Intensity
• Ground Motion & Liquefaction
• Earthquake Resistant Design
• Seismic Zones
• Reinforcements
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Earthquakes
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Earthquakes
• When an earthquake occurs, the
elastically stored energy is carried
outward from the FOCUS to other
parts of Earth by vibrations called
seismic waves.
• The seismic waves released in the
earthquake spread out spherically in
all directions and touch the surface
first at the EPICENTRE.
• Seismic waves are elastic
disturbances, so unless the ELASTIC
LIMIT of the rock is exceeded there
will be NO permanent deformation
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Earthquakes
• Earthquake Magnitude
• An earthquake has one
magnitude unit independent of
its location
• Magnitude of an Earthquake is
measured using a Seismometer
which produces a Seismograph
• Richter Scale and Moment
Magnitude Scale (MMS) are used
to categorize earthquakes.
• MMS can measure the Richter
magnitude(ML), Body wave
magnitude (Mb) and surface
wave magnitude (Ms)
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Earthquakes
• Earthquake Intensity
• Earthquake Intensity measurement is
an on-the-ground description and
explains the severity of earthquake
shaking and its effects on people and
their environment.
• Intensity measurements will differ
depending on each location’s nearness
to the epicenter.
• The Modified Mercalli (MM) Intensity
Scale which is based on Giuseppe
Mercalli's Mercalli intensity scale of
1902, is used. The scale is composed
of increasing levels of intensity that
range from observable quake impacts
from light shaking to catastrophic
destruction.
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Ground Motion
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Ground Motion
• Ground motion is the movement of the Earth's surface produced by
seismic waves from earthquakes or explosions.
• Knowledge of local amplification of ground motion is very important in
order to choose the suitable design solutions.
• Local amplification can be anticipated from the presence of particular
stratigraphic conditions, such as soft soil overlapping the bedrock, or
where morphological settings may produce focalization of the seismic
event.
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Ground Motion
• In April 2015, Nepal experienced an
earthquake, 7.8 on the Richter scale, with its
focus was only 11km.
• Ground motion from the shallow focus cause
extensive damage to structures and building.
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Soil Liquefaction
• Soil liquefaction occurs when a cohesionless saturated or partially
saturated soil substantially loses strength and stiffness in response to an
applied stress such as shaking during an earthquake or other sudden
change in stress condition, in which material that is ordinarily a solid
behaves like a liquid.
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Soil Liquefaction
• In the region of Palu in Indonesia the 7.5 earthquake on September 28,
2018 caused much damage by so-called soil liquefaction. Due to the forces
of the seismic shocks, the sandy ground got liquid and started to flow in a
direction washing away trees and houses. More than 800 were killed.
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https://www.iitk.ac.in/nicee/EQTips/EQTip11.pdf
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Summary
• Earthquake resistant construction is important in
earthquake prone area
• The design must resist earthquakes with almost no
damage
• The building must not collapse or harm human lives
during severe earthquake motions
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Important Links
• https://nidm.gov.in/safety_earthquake.asp
• Simplified guideline for all new buildings of seismic zone III of India
• Simplified guideline for all new buildings of seismic zone IV of India
• Simplified guideline for all new buildings of seismic zone V of India
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Next lecture
• Soil – Classification, Erosion and Conservation