earthquake resistant structural system 14.12.2006

7/30/2019 Earthquake Resistant Structural System 14.12.2006

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EARTHQUAKE RESISTANT

STRUCTURAL SYSTEMS

Dr. K.NagamaniProfessor

Structural Engineering Division

College of Engineering, Chennai-25.


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As is said often quakes dont kill

people, it is the unsafe buildings, whichdo. The Bhuj quakes aftermath is aliving example of this.

codes are not mandatory and hence notadhered to. As a result, even structures

in urban areas like Ahmedabad crashedliterally like a pack of cards.


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Loading Pattern and ResultingInternal Structural Actions

Level 1

The frame

Level j

Level j+1

Roof

OturningMoment

Forces Shear forces


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Types of Control Structures

Conventional structures

Passive vibration Control

Semi-Active and Active vibrationControl


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Configuration

architectural shape and size;

type, size and location ofstructural elements;

type, size and location of non-structural elements.


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PLAN OF

BUILDING

(Asymmetry should be

avoided)

Asymmetricbuildings

undergo torsionand the extreme

corners ofasymmetric

buildings aresubjected to very

large earthquakeforces


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GENERAL SHAPE OF BUILDING

Very slender

buildings should

beavoided

Inverted pendulum type buildings areunstable


9/81Sudden change in lateral stiffness should be

GENERAL SHAPE OF BUILDING


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Projections and large overhangs

Avoid long projected

balcony

Large projections

should be avoided


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Floating columns

Large overhangs, projections and floating columns attract largeearthquake force and therefore likely to damage/collapse due tounstability

S ti f di i il


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Separation of dissimilar

buildings

To avoid

collision,

adjacent

dissimilarbuildings should

be separated by a

minimum gap

Type of construction Minimum gap

per storey(mm)

Load Bearing Building 15

RCC Frame Building 20

Steel Frame Building 30


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Buildings

with softstorey


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Weak beamand strong

columndesign


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Conventional

Structural SystemsThe main vertical resisting systems

for earthquakes are:

shear walls;

braced frames; moment resisting (or rigid) frames.


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Horizontal 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


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Shear Walls

Shear walls are vertical walls that are designedto receive lateral forces from diaphragms andtransmit them to the ground. The forces in

these walls are predominantly shear forces inwhich the fibers within the wall try to slide pastone another. When you build a house ofcards, you design a shear wall structure, and

you soon learn that sufficient card "walls" mustbe placed at right angles to one another or thehouse will collapse.


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Shear Walls

B d F


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Braced Frames

Braced frames act similarly to shear walls.The most common material for braced-frame construction is steel in the form ofrolled sections or tubes. Where diagonal

bracing is used, the braces in compressionare sometimes ignored because ofbuckling. Where the bracing is in onedirection only (within the plane of the

braced frame) the diagonal member mustbe proportioned to prevent buckling when incompression.


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Moment Resistant Frames


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Non-structural Components

It is common place for engineers to ignore thestructural effect of these elements. In some

cases the non-structural elements provide

accidental strength to the building. They may, however, interfere adversely with

the structural behaviour of the essential load-carrying structure.

This could lead to unanticipated overstressingof essential load-carrying members.


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Nonstructural Components

Partition walls

Architectural Elements

Mechanical Elements


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HEAVY MASS ON TOP - W.T. COLLAPSE

WHIPPING EFFECT


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Basic Configuration Issues and

Structural Response

The size of a building

The height of a building

horizontal dimensions

height/width ratio to 3 or 4

symmetry

redundancy

soft storey concept is very dangerous

strong column weak beam


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A WEAK COLUMN -

STRONG FLOOR SYSTEM


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A WEAK COLUMN -

STRONG BEAM SYSTEM


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WEAK COLUMN - STRONG BEAM SYSTEM


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WEAK COLUMN-STRONG ROOF SYSTEM


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EXCESSIVE TOP CANTILEVERS


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HEAVY CANTILEVER FRONT FACADE


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HEAVY MASS ON TOP - W.T. COLLAPSE

WHIPPING EFFECT


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Insufficient connection between the RC elevator core

and rest of the building lead to the underutilization of

the lateral strength and stiffness of the elevator core


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Collapse of upper storey of a building

at Gandhidham. It is suspected that this

may have been caused by inadequate

lap lengths in the column

reinforcement.


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No building is earthquake-proof. But a properly engineered tall

building should be able to withstand the maximum credible

earthquake for its area without collapse, and lesser seismic eventswithout major structural damage,

says R. Shankar Nair, Chairman of Council on Tall Buildings

and Urban Habitat, Chicago.

Of course, mistakes do happen, even in the U.S. But if

American standards of design and construction had prevailed in

the Bhuj area (an economic impossibility, of course), there

would have been casualties from the collapse of a few small

buildings and from falling objects, but no large, recently-built

multi-storey building should have collapsed.


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Materials

high ductility;

high strength-to-weight ratio;

homogeneity;

ease in making full-strength

connections.


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Some Advanced Earthquake

Resistant Techniques

Base Isolation

Energy Dissipation Devices


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Energy Dissipation Devices

Friction Dampers

Metallic Dampers

Viscoelastic Dampers Viscous Dampers


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What is Structural Control?

Mechanical system employed to reduce structural vibrations

Control deviceControl algorithms Enhance the safety and habitability of structures Interested in numerous sources of vibration

Winds (Strong gusts and typhoons)Earthquakes (Weak and strong)Machinery Types of structural controlPassive (Very common approach to control)

ActiveSemi-Active


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Concept of Semi- and Active

Control

Two approaches to the employment ofactive and semi-active structural controlsystems:

Feed-back control (most common)

Feed-forward control (least common)


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Passive Structural Control

Tend to be very simple systems

Requires no external power to operateSimply impart forces which are developed inresponse to structures motion

Relatively inexpensive solution to reducingstructural vibrations

Usually compact and non-invasive to

architectural spaces Limits exist on the amount of control attainable


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Passive Control Device Types

Viscoelastic Dampers:

Contains a viscoelastic polymer

sandwiched between two metal plates.

Viscoelastic polymer deforms through

shear action removing energy from thesystem.


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Viscoelastic Polymer BraceDamper

Cylindrical viscous damper (CVD) a


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Cylindrical viscous damper (CVD), adamper using the shearing resistance of aviscous fluid, consists of three concentric

steel tubes filled with viscous fluid.


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CVD


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Lead Extrusion Damper

T i l i t ll ti (b ) f


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Typical installation (brace) ofLead Extrusion Damper

Bingham Material damper, using viscous


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g p , gresistance of a special filler, consists of a fluid filled

cylinder, a piston and a rod.

The Oiles Viscous Wall Damper is a vibration attenuator


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p

using the shear resistance force of a highly viscous fluid.


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Base Isolation

lead-rubber bearings

These are among the frequently-usedtypes of base isolation bearings

B I l t d d Fi d B


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Base-Isolated and Fixed-Base

Buildings


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Lead-Rubber Bearing

B I l t d Fi d B


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Base-Isolated, Fixed-Base

Buildings

BASE ISOLATION SYSTEM


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BASE ISOLATION SYSTEM

Without Base Isolation With Base Isolation


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Wh t i th T d M D S t ?


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What is the Tuned Mass Damper System?

This is a system for absorbing the vibrations within a

building generated by high winds or an earthquake.There are two main systems classified as passive controland active control. The passive control systems, such usa TMD (Tuned Mass Damper) using a weight whichoscillates at the same period as the building does and an

additional damper that connects two relatively movingpoints when the building oscillates, absorbs thevibrations automatically without the need of an electricalcontrol system. The active control systems use acomputer-controlled actuator to realize the best

performance. They are AMD (Active Mass Damper)which suppresses the oscillation of a building byactuating a weight and an ABS(Active Brace System)which controls axial forces of braces and others.


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Function

During an earthquake or strong wind, every

building shakes at its own natural perioddepending on its rigidity and size.TMD-RP and AMD (Active Mass-added Damper)move so that the additional mass of the vibration

control system offsets the motion of the buildingto absorb vibration energy.


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A Second Type of Base Isolation:


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Seco d ype o ase so at oSpherical Sliding Isolation

Systems

Damping Devices and Bracing


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Damping Devices and Bracing

Systems

Examples of Building


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Examples of Building

Applications

San Francisco Airport International Terminal Owner: City & County of San Francisco Engineer: Skidmore, Owings & Merrill Friction PendulumTM seismic isolation of this

new building protects the expansive glassexterior walls and the long span rooftrusses. Use of FrictionPendulumTM bearings, instead of the

equivalent rubber bearings, saved 600 tons ofstructural steel. With over 1.2 million sq. ft. ofsupported space, it is the largest seismicallyisolated building in the world.
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U.S. Court of AppealsOwner: General Services AdministrationEngineer: Skidmore, Owings & Merrill

Seismic retrofit of this historic building usingFriction PendulumTM bearings saved $7.6million in construction costs and 80,000 sq. ft. ofbasement space, compared to the rubber

bearing design. The project won the 1994 GSADesign Award for Engineering, Technology &Innovation
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American River Bridge

Isolation Bearings Lower Construction Costsand Double Seismic Resistance Capacity

The American River Bridge at Lake Natoma in Folsom, California, isf th l t b id t i i i l ti F i ti


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one of the largest new bridges to use seismic isolation. FrictionPendulumTM seismic isolation allows the bridge to elastically resistthe safety level earthquake, with no structural damage.

The use of seismic isolation bearings saved $1 million inconstruction costs, compared to the non-isolated bridge design. Theconstruction cost savings came from a reduction in the size of thedrilled caissons. Seismic force demands for the non-isolated bridgedesign, would have been more than twice the bridges's elasticstrength capacity. Consequently, a non-isolated bridge would havebeen expected to sustain structural damage during the safety leveldesign earthquake event.

The bridge structure consists of two post-tensioned concrete boxframes on piers supported by 8 foot diameter drilled caissons. The48 Friction PendulumTM bearings are located on top of the piersand abutments. The bearings have a 10 inch displacement capacityand support dead plus live loads of up to 4 million pounds. Thebearings were installed pre-displaced so as to accommodateconstruction movements from post-tensioning and concreteshrinkage.


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White River Bridge

Seismic Isolation Bearings Subject ToExtreme Cold Temperatures

The new White River Bridge constructed in the Yukon,C d i t d 9 F i ti P d l TM i i


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Canada, is supported on 9 Friction PendulumTM seismicisolation bearings. It is a 590 feet long, steel girderstructure consisting of 2 spans which carry 2 lanes oftraffic. Use of Friction PendulumTM seismic isolationbearings achieved an elastic structure response for thedesign level earthquake (0.2g peak ground acceleration),at a substantially lower cost than would have beenpossible without isolation bearings.

Because of its location in northern Canada, the White

River Bridge is subjected to extreme temperatures. TheFriction PendulumTM seismic isolation bearings are ableto maintain their design properties over a wide range oftemperatures, including extreme cold conditions. Thebearings maintained their design stiffness and damping

when tested over a temperature range of -94F to+140F. When tested at temperatures as low as -166F,they demonstrated stable performance without incurringbearing damage.


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Emergency Operations CenterOwner: State of WashingtonEngineer: KPFF Consulting Engineers

Friction PendulumTM seismic isolation ofthis essential emergency facility ensurescontinued operations following an

earthquake.
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Citicorp Building NYC-TMD

Built in 1978 with an unusual base

400 ton TMD installed on top

Deflections reduced by 40%

The mass moves in the opposite directionto building movement


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ACTIVE MASS DAMPER(AMD)

During winds and small earthquakes Large mass whose motion is controlled by an

actuator

Velocity feedback system

Mass of AMD is 1% of the building weight

Need large amount of power

20% damping in first mode and 5% in second

mode With the AMD at top, displacement at roof level

is reduced by to 1/3


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Kyobashi Siewa Building

1989, Tokyo, Japan

Extremely narrow building(33mx4m)- 10Stories Steel Construction

First Active structural controlled building inthe world

system: TMD


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system: TMD

Crystal Tower Osaka Prefecture (Completed in1990)Design: Takenaka CorporationTotal Floor Space:85,994 m2Number of floors: 2 floors below ground, 37floors above groundStructural control device:TMD with six 90t weight masses (Utilizing crystalice heat storage tanks)

Object: Vibration control for a building againstheavy wind(Transverse movements in two directions )

Crystal Tower Osaka Prefecture


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Application of vibration control


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Application of vibration control

structure system: AMD

Applause Tower Osaka Prefecture (Completedin 1992)Design: Takenaka CorporationTotal Floor Space:96,793 m2Number of floors: 3 below ground, 34 abovegroundStructural control device: AMD, mass weight480t(Utilizing a heliport)

Object: Suppression of building vibration instrong winds or medium/small earthquakes(Parallel movements in two directions)

A l T


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Applause Tower


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THANK YOU

earthquake resistant structural system 14.12.2006

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