seminar roll no 09 prashant

7/29/2019 Seminar Roll No 09 Prashant

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PRESENTED BY : PRASHANT CHOUGULE

ROLL NO : 3809

GUIDED BY : PROF.SAHARE

Seminar on Base Isolation

Technique of Earthquake Engg


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What is an earthquake?

An earthquake is the result of a sudden release of energy inthe Earth's crust that creates seismic waves.


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Effects of Earthquake

ShakingandGroundrupture


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LandslidesandAvalanches


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Fires


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Soilliquefaction


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Tsunami


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Floods


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Techniques used to reduce theeffects of earthquake on building

structures

Shear Walls

Braced Frames

Tuned Mass Damper

Base Isolation


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Shear Walls

Shear walls

are verticalelements ofthe horizontalforceresistingsystem.


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Functions of Shear Wall

Shear walls must provide the necessary lateral strength to resist

horizontalearthquake forces.

When shear walls are strong enough, they will transfer these

horizontal forces to the next element in the load path below them.

Shear walls also provide lateral stiffness to prevent the roof or floor

above from excessive side-sway.

Buildings that are sufficiently stiff will usually suffer less

nonstructural damage.


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Braced Frames

A Braced Frame is

a structural system

which is designed

primarily to

resist wind and

earthquake forces.


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Types of Braced Frames

Knee Braced Frame Diagonal Frame


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Types of Braced Frames

X-Frame K-Frame


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Advantages Disadvantages

Braced Frames

High Strength and Stiffness

Efficient and Economical

Compact

Obstructive

Low Ductility


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Tuned Mass Damper

A tuned mass

damper, also known

as an active mass

damper (AMD), is a

device mounted in

structures to reduce

the amplitude of

mechanical

vibrations.

TMD

weighing730 tons inTaipei 101


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Tuned Mass Damper

Principle :Tuned mass dampers stabilize against violent motion

caused by harmonic vibration. A tuned damper reduces the

vibration of a system with a comparatively lightweight component

so that the worst-case vibrations are less intense.


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Examples of buildings and structures with TunedMass Dampers

Taipei 101,Taiwan

One Wall Centre in Vancouver

Shanghai World Financial Center , China

Berlin Television Tower

Dublin Spire in Dublin, Ireland

London Millennium Bridge

Grand Canyon Skywalk, AZBurj al-Arab, Dubai(11 TMD)

Located at82nd Storey
http://en.wikipedia.org/wiki/One_Wall_Centrehttp://en.wikipedia.org/wiki/One_Wall_Centre


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Base Isolation

Concept :The term Base Isolation uses the word isolation in its

meaning of the state being separated and base as a part that

supports from beneath or serves as a foundation for an object or

structure.


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Base Isolation

Principle :The fundamental principle of base isolation is to modify

the response of the building so that the ground can move below

without transmitting these motions into the building.


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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 so in regions of high

seismicity)

Common practice is to design them so that they experience damage

in a controlled manner and have large inelastic displacements

potential


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Response of Base Isolated Buildingsversus Fixed Base Structure

Reduced

Superstructure

Deformations for

Base Isolated

Structure

Drift on Isolation Interface


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Response Spectrum Analysis ofFixed Base Structure v/s BaseIsolated Structure

Significantly

Increase the Period

of the Structure and

the Damping so

that the Response isSignificantly

Reduced

Period

Fixed Base

Base Isolated


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Base Isolation in Buildings

Original Structure Isolated Structure

Isolation at foundation levelFixed Base Structure


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Types of Base Isolators

Base Isolators

ElastomericBearings

Low DampingRubberBearing

High DampingRubberBearing

Lead RubberBearing

SlidingBearings

Flat SlidingBearing

FrictionPendulum

System


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Low or High DampingRubber Bearing

Lead Rubber Bearing

Elastomeric Bearing


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Sliding Bearing

Friction

PendulumSystem


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Base Isolation Explained


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Merits and Demerits of Base Isolators

Device Merits Demerits

Low DampingRubber Bearing

Low in structure accelerationsHigh Displacements

Low Damping

Low costNo Resistance to service loads

P- moments top and Bottom

High DampingRubber Bearing

Moderate in structure accelerationsStrain dependent stiffness and damping

Complex Analysis

Resistance to service loadsLimited choice of stiffness and damping

Change in properties with scragging

Moderate to High Damping P- moments top and Bottom

Lead RubberBearing

Moderate in structure accelerations Cyclic change in properties

Wide choice of stiffness/damping P- moments top and Bottom


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Merits and Demerits of Base Isolators

Device Merits Demerits

Flat Sliders

Low profile High in structure accelerations

Resistance to service loads Sticking

High DampingNo restoring force

P- moments can be top or Bottom

High DampingRubber Bearing

Low profile

High in structure accelerationsResistant to service loads

Moderate to high damping

P- moments can be top or BottomSticking

Reduced Tension Response


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Performance in real earthquakes

StructureSystem

TypeEarth-quake

Comments

USC Hospital LRB 1994Northridge

Movement up to 45mmNo Damage & continued operation

LA country Fire

House

HDR 1994

Northridge

Minor ceiling damage

Continued OperationFoothills Law &Justice Center

HDR 1994Northridge

No damageSystem not activated

Tohuku ElectricPower

LRB 1995 Kobe No damageMovement up to 120mm

Eel River Bridge LRB 1992 CapeMendocino

Movement up to 200mm L & 100mmTMinor joint spalling

Te Teko Bridge(NZ)

LRB 1987Edgecumbe

Estimated Displacement 100mmAbutment bearing dislodged ,caused minordamage


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Isolation System Suppliers

Company Product

Bridgestone (Japan)BTR Andre (UK)

Seougal Rubber Corporation (US)High Damping Rubber

Robinson Seismic (NZ) Lead Rubber

Earthquake Protection Systems ,Inc (US) Friction Pendulum System

Dynamic Isolation Systems,Inc (US)Skellerup Industries (NZ)

Seismic Energy Products (US)

Lead Rubber ,High Damping Rubber

Hercules Engineering (Australia)R J Watson ,Inc (US)

FIP-Energy Absorption Systems (US)Sliding Bearings


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Case Study of San FranciscoCity Hall


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San Francisco City Hall

Built in 1915

Today recognized as oneof the most notableexamples of classicalarchitecture in the U.S.

Nearly 300 feet tall

Steel Frame withconcrete slabs


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The Building was severely damaged during the 1989 LomaPrieta earthquake.

Four Retrofitting strategies were estimated forreconstruction of San Francisco City Hall to prevent it from

future earthquakes.


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Four Retrofit

Strategies wereconsidered

Base Isolation Fixed Base /Concrete ShearWalls

Fixed Base /Steel Braced

FramesFixed Base /

Steel MomentFrames

Flexible Story


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Based on the results of the analysis, theBase Isolation Scheme was selected as best

meeting the retrofit objectives andproviding the most favorable performance

for the least relative cost

Base Isolation is considered a particularly effectivestrategy when applied to massive (and rather stiff)

structures


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More Examples of Base IsolatedBuildings

Union House,

Auckland

FlexuralSteelDissipatersat groundlevel


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Bhuj

Hospital,Gujarat


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Christchurch

WomensHospital


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Conclusion


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Any Questions???


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THANK YOU

seminar roll no 09 prashant

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