shubham dubey seminar
TRANSCRIPT
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A
Seminar
On
“ Base Isolation using dampers in
Civil Engineering”
CIVIL ENGINERING DEPARTMENT
INDIAN INSTITUTE OF TECHNOLOGY
VARANASI-221005
Prepared By: Shubham Dubey (11403EN001)
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CONTENTS
• What is seismic force?
• Difference between magnitude and intensity.
• Natural hazards due to earthquake.
• Basic concept of earthquake resistant diesign.
• Requirements and different types of base isolation devices.
• Case study – Los Angeles city hall
• Bibliography.
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WHAT IS SEISMIC FORCE?
Seismic Forces is generated due to
Earthquake.
Earthquake is a natural disaster. It is a violent shaking of earth.
It happens due to mass shifting in
bedrock.
Because it is a natural disaster so
we can’t control it. Only we can
try that the damage should be
minimum.
Bhuj Earthquake, 2001
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Different Seismic Zones In India
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MAGNITUDE AND INTENSITY
OF EARTHQUAKE1. MAGNITUDE
• The Magnitude (M) is a quantitative measure of its strength in
terms of energy released .
• It is defined as logarithm to the base 10 of the maximum trace
amplitude, expressed in microns, which the standard short-
period torsion seismometer would register due to theearthquake at an epicentral distance of 100 km.
It is measured in R ichter’s scale.
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2. INTENSITY
The intensity of an earthquake is measured qualitatively in
terms of damages caused by it at a particular location.
In general, larger the earthquake, greater is the intensity
It is indicated by a number according to the modified Mercalli Scale or
M.S.K. Scale of seismic intensities
Magnitude of an earthquake is a measure of its
size. While intensity is an indicator of the severity
of shaking generated at a given location.
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HAZARDS DUE TO EARTHQUAKE
a) Liquefaction of Soils
b) Ground Shaking
c) Surface Ruptured) Landslides
e) Lateral Spreading
f) Shear Failure of Foundation
g) Settlements of Structures
h) Failure of Retaining Wall
i) Tsunamis And Seiches
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CONVENTIONAL CONSTRUCTIONPRACTICE ASSUMES FIXED BASE
STRUCTURES
• The Dynamic Characteristics of Fixed Base Structures are
determined by the general characteristics of the structuralsystem
• The Designer can only slightly adjust those DynamicCharacteristics
• As a matter of fact, most common Building Structures haveunfavorable Dynamic Characteristics that result in increasedSeismic Response
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EARTHQUAKE PERFORMANCE
OF FIXED BASE STRUCTURES
• Conventional Fixed Base Structures can not be realistically
designed to remain elastic in large seismic events (more soin regions of high seismicity)
• Common practice is to design them so that they experiencedamage in a controlled manner and have large inelastic
displacements potential
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EARTHQUAKE-RESISTANT DESIGN
Objective of Earthquake-Resistant Design is to make such
buildings that can resist effect of ground motion and would not
collapse during the strong Earthquake.
All the components of the structure and foundations are
designed to resist inertia forces in addition to the normal
forces.
All the walls must be jointed properly, so that they can act
together against the earthquake shaking at the time of seismic
force transferring to the ground.
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BASE ISOLATION METHOD
The idea behind the 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.
If a building is rested on flexible pads that offer resistance against
lateral movements, then some effect of the ground shaking will be
transferred to the building above. If the flexible pads are properly
chosen, the forces induced by ground shaking can be a few times
smaller than that experienced by the building built directly on
ground.
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BASIC IDEA BEHIND BASE
ISOLATION
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THE CONCEPT OF BASE
ISOLATION
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THE CONCEPT OF BASE ISOLATION
Fixed Base
Base IsolatedPeriod
Significantly Increase thePeriod of the Structure and the
Damping so that the Response
is Significantly Reduced
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EFFECT OF BASE ISOLATION
METHOD
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View of Basement in Bhuj Hospital Building
BASE ISOLATION METHOD
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• REQUIREMENT OF BASE
ISOLATION DEVICES
• Isolating the building from the ground
• Supporting the weight of building
• Damping of response amplitude
• Restoring the original position after an earthquake
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SEISMIC DAMPERS
Seismic Dampers are fixed in place of structural elements as
diagonal braces.
They absorb a part of seismic energy when it is transmitted through
them.
TYPES OF SEISMIC DAMPERS:
a. Viscous DampersEnergy is absorbed by silicone-based
fluid passing between piston-cylinder
arrangement.
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Viscous Damper
SEISMIC DAMPERS
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SEISMIC DAMPERS
b. Friction Dampers
Energy is absorbed by surfaces with
friction between them rubbing against
each other
c. Yielding Dampers
Energy is absorbed by metallic
components.
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Friction And Yielding Dampers
SEISMIC DAMPERS
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Steel damper
Lead
damper
BASE ISOLATION SYSTEM DAMPERS
Oil damper
Friction damper with
Coned disc springs
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MAINTENANCE
• Large relative displacement at isolation interface occurs during strong
earthquake. Thus, obstacles in or in the vicinity of isolation interface
spoil efficient seismic performances.
• Some isolation devices deteriorate by aging. Aged deteriorations must beconsidered by heat accelerated tests and others at design stage.
• Rubber bearings creep subjected to long term loads. Unexpected creeps
and external damages must be found out by regular examinations.
• Breaks, water leakage and others may happen when piping and wiringhave insufficient deformation capacities.
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LOS ANGELES CITY HALL
• Building was severely damaged during the 1989 Loma
Prieta earthquake
• Building is listed on the historic register – Retrofit had to
preserve the interior architecture and the historic fabric ofthe building
• Both conventional fixed-base and base isolation retrofit
concepts were studied
• The most economical and effective method was determined
to be base isolation
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LOS ANGELES CITY HALL
Isolation System:
• 111 rubberisolation bearings
• 36 of them with
lead cores
Fixed Base Base Isolated
Earthquake Response
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LOS ANGELES CITY HALL
Critical Construction Issues:
• Temporary lateral bracing during construction period to
safeguard against possible earthquake occurrence
• Symmetric work sequence was important to reduce the
possibility of torsional response in the event of an
earthquake
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CONCLUSION
• Thus the conclusion is that
base isolation is the most
appropriate and economical
way of designing a seismic
load resisting multi storeystructure . Moreover, research
work is going on whether the
absorbed seismic energy can
be utilized in some or the
other way.
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BIBLIOGRAPHY
• Calvi, G.M., (2010). L’Aquila Earthquake 2009: Reconstruction between Temporary and
Definitive. Proceedings, NZSEE 2010 Annual Conference. Wellington.
• Christopoulos, C. and Filiatrault, A., (2006). Principles of Passive Supplemental Damping and
Seismic Isolation. IUSS Press. First edition. Pavia, Italia.
• Dowrick, D.J., (1988). Earthquake Resistant Design. John Wiley & Sons, Chichester, UK.
• Rodgers G.W., Solberg, K.M., Mander J. B., Chase, J.G., Bradley, B.A., and Dhaka R.P.,
(2011). ‚High-Force-to-Volume Seismic Dissipaters Embedded in a Jointed Pre-Cast Concrete
Frame‛. ASCE Journal of Structural Engineering (JSE), ISSN: 0733-9445, (In Press).
• Rodgers, G.W., Solberg, K.M., Chase, J.G., Mander, J.B., Bradley, B.A., Dhakal, R.P. and Li,
L.,
• (2008). ‚Performance of a damage-protected beam-column subassembly utilizing external
• HF2V energy dissipation devices‛. Earthquake Engineering and Structural Dynamics, Vol. 37,
No. 13, pp. 1549-1564.
• Skinner, R.I., Kelly, T.E., Robinson, W.H., (2000). ‚Seismic Isolation for Designers and
Structural Engineers‛. Robinson Seismic Ltd. and Holmes Consulting Group, Wellington.
• Zayas, V.A. et al., (1990). A Simple Pendulum Technique for Achieving Seismic Isolation.
Earthquake Spectra.pp. 317, Vol.6, No.2.
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