Seminario Internacional de Estructuras con disipadores de Energía

Seismic Design of Nonstructural Building Components

January 12-15, 2015

Quito, Ecuador

Chapter 10Introduction to Seismic Isolation and Dissipation

Seismic Design and Analysis of Nonstructural Components

Andre Filiatrault, Ph.D., Eng.


January 12-15, 2015

Quito, Ecuador

CONTENT

1. Fundamental Concepts

2. Categories of Supplemental Damping and Seismic Isolation Systems

3. Hysteretic Dampers

4. Viscous Dampers

5. Laminated Rubber Bearings

6. Lead-rubber Bearings

7. Friction Pendulum System


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Basic performance objective of conventional seismic design: life safety

Life safety performance objective not sufficient for important structures

To increase seismic performance level at reasonable cost: supplemental damping and seismic isolation


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Not

O.K.

O.K.


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Supplemental Damping Systems:

Special devices mechanical dampers

Mechanical energy dissipation through heat by movements of the structural elements

Protect main structural elements

If all seismic energy dissipated mechanically: no damage


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Seismic Isolation Systems:

Installation of isolators beneath supporting points of the structure

Buildings: isolators located between superstructure and foundation

Bridges: isolators located between deck and piers

Isolators have much lower lateral stiffness than superstructure

Isolators limit transfer of seismic energy to superstructure

If no seismic energy transmitted to superstructure: no damage


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Components of Seismic Isolation Systems:

Isolator

Lateral stiffness much less than superstructure

Increase effective period of vibration

Sliding surface, rubber pad, etc.

Supplemental damping mechanism

Dissipate residual seismic input energy

Limits displacements of isolator

Reduces force transmitted to superstructure


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Components of Seismic Isolation Systems:


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E-Defense Experiments: 5 story steel moment frame


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Illustrative Example


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Point A: original portal frame, T = 1.0 sec

Point B: portal frame with added viscous damper, z = 20%, T = 1.0 sec

Point C: portal frame with added hysteretic damper, z = 20%, T = 0.55 sec

Point D: portal with added bracing system, z = 5%, T = 0.55 sec

Point E: base isolated portal frame, z = 5%, T = 2.0 sec

Point F: base isolated portal frame, z = 20%, T = 2.0 sec


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It is a combination of period shift and added energy dissipation that must be

considered jointly in order to fully understand the effectiveness of added

supplemental damping devices and/or base isolation systems on the seismic

response of a structure.

Note: Behavior and analysis more complex if structure undergoes

inelastic deformations


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2. Categories of Supplemental Damping and Seismic Isolation Systems

Discussed in this presentation


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Metallic Dampers

Hysteretic Behaviour of Yielding Steel Elements


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3. Hysteretic Dampers Metallic Dampers

Geometrical Considerations Metallic dampers can be used as part of chevron bracing systems.

Yielding devices dissipate energy through relative horizontal. displacement between apex of chevron and above floor level.

If metallic plates used, act as fixed-fixed beams.

To distribute inelastic strains, it is desirable that plastic moment at any section be reached simultaneously.

Geometry of the device must be optimized.


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3. Hysteretic Dampers Geometrical Considerations


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Geometrical Considerations



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Experimental Studies Added Damping - Added Stiffness Systems (ADAS)

System Testing (Whittaker et al. 1991)


Video


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Experimental Studies Triangular Added Damping Added Stiffness (TADAS) Systems

Developed by Tsai et al. (1993).

Variation of ADAS system using triangular metallic plate dampers.

Triangular plates rigidly welded to a top plate but simply connected to a slotted base.

Main advantages of TADAS:

Not affected by gravity loads because of slotted holes in base plate.

No rotational restraint required at the top of the brace connection assemblage.

Disadvantages of TADAS:

Construction more complicated.

Careful welding required.



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Experimental Studies Cast Steel Yielding Fuse For

Concentrically Braced Frames

Developed by Gray et al. (2010) at the University of

Toronto, Canada.

Ductile cast steel connector in a concentrically braced

frame.

Seismic energy dissipated through inelastic flexural

yielding of specially designed

yielding elements similar to

TADAS elements in the cast

connector.


http://www.youtube.com/watch?v=TAXpwimvbjA


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Experimental Studies Cast Steel Yielding Fuse For

Concentrically Braced Frames

Main advantages:

No welding or bolting in the connector.

Stable hysteretic response with tension

stiffening at large

displacements.

Main disadvantage:

Cost?

Tested at full-scale at the University of Toronto.



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Experimental Studies Lead Extrusion Devices (LED)

Developed in the mid-1970s in New Zealand (Robinson and Greenbank 1976).

Metallic dampers that take advantage of extrusion of lead through orifices.

Two different types of LED devices: constricted tube and bulged shaft.



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Component Testing



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Desirable characteristics of LED dampers:

Hysteretic behaviour is stable and repeatable and is unaffected by number of load cycles.

Environmental factors have no significant influence on the behaviour.

Fatigue is not a major concern since lead is hot worked at room temperature.

Strain rate has only a minor effect on the hysteretic response.

Tests have demonstrated insignificant aging effects.



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Experimental Studies Buckling Restrained Braces (BRB) / Unbonded Braces

Originally manufactured by Nippon Steel Corporation in Japan.

Steel core plate encased in a steel tube filled with concrete.

Steel core carries the axial load while the outer tube, via the concrete, provides lateral support to the core and prevents global

buckling.

Thin layer of lubricating material at the concrete interface.

Cyclic qualification tests included in AISC Seismic Requirements.



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Experimental Studies Buckling Restrained Braces (BRB) / Unbonded Braces


http://www.youtube.com/watch?v=_jUJ8Jv1ZPg


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Structural Implementations


Unbonded Braces inNew 4-story Central Dining Facility

Stanley HallUC Berkeley, 2003

Photo: Courtesy of M. Constantinou


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Friction Dampers

Studies on the Variation of Coefficient of Friction for Metal-Metal Interfaces Tremblay and Stiemer (1993)



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Friction Dampers

Studies on the Variation of Coefficient of Friction for Metal-Metal Interfaces Grigorian et al. (1993)



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Existing Friction Damping Systems Slotted-Bolted Connections

Simplest form of friction dampers.

Slotted-bolted connections at the ends of conventional bracing members.

To maintain constant slip load, disc spring washers can be used.



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Existing Friction Damping Systems Slotted-Bolted Connections



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Existing Friction Damping Systems Sumitomo Friction Device (Sumitomo Metal Industries Ltd.,Japan)

More sophisticated friction device.

Incorporates a pre-compressed internal spring that induces a force that is converted through the action of inner and outer wedges into a

normal force on copper alloy friction pads containing graphite plug

inserts for lubrication.



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Existing Friction Damping Systems Pall Friction Device (Pall Dynamics Ltd., Canada)

Most implemented friction damping system.

Designed to be mounted in a moment-resisting framed structure.

Mechanism containing slotted slip joints introduced at intersection of frame cross-braces.



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Video


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Concordia University Library,

Montreal, Canada, 1991


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Freeport Water Tower, Sacramento,

CA, 1999


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Boeing Plant, Seattle, Washington,

2001


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4. Viscous Dampers

Linear Viscous Dampers

Hysteretic Response


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4. Viscous Dampers

Nonlinear Viscous Dampers

Fluid type dampers can be designed to behave as nonlinear viscous elements by adjusting their silicone oil and orificing characteristics.

Main advantage of nonlinear viscous dampers is that in the event of a velocity spike, the force in the viscous damper is controlled to avoid overloading the damper or the bracing system to which it is connected.


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4. Viscous Dampers

Nonlinear Viscous Dampers


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4. Viscous Dampers Typical fluid dampers incorporate a stainless steel piston with a

bronze orifice head.

Device filled with silicone oil.

Piston head utilizes specially shaped orifices that alter flow characteristics with fluid relative velocity.

Force produced by damper is generated by the pressure differential across piston head.


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4. Viscous Dampers Various structural models, with and without fluid dampers

manufactured by Taylor Devices Inc., tested on the shake table at the University at Buffalo from 1991 to 1995.

e.g. 1/4 scale 3-storey test structure (Constantinou et al. 1993).

Model had weights = 28.5 kN distributed equally on the three floors.


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4. Viscous Dampers


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4. Viscous DampersWoodland Hotel, Woodland, CAFour-story reinforced concrete/shear

wall buildingConstructed in 192716 Taylor Dampers installed

horizontally Capacity of each damper = 100 kips


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4. Viscous DampersSan Francisco Civic Center

292 Fluid Viscous Dampers Installed In Line

Courtesy of M. Constantinou


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YERBA-BUENA TOWER, SAN FRANCISCO

37-STORY WITH REVERSE UPPER TOGGLE

SYSTEM. UNDER CONSTRUCTION 2001.

20 FLUID DAMPERS IN UPPER STORIES.


4. Viscous Dampers


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4. Viscous Dampers

OLYMPIC COMMITTEE BUILDING, CYPRUS

3-STORY, V-SHAPED IN PLAN

52 SCISSOR-JACK ASSEMBLIES

COMPLETED JULY 2006 Courtesy of M. Constantinou


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Laminated rubber bearings (elastomeric bearings) used extensively for bridge superstructures to accommodate temperature-induced movements deformations.

In last 20 years, use extended to seismic isolation of buildings and other structures.

Lead-rubber (lead-plug) bearing: Elastomeric bearing with central lead plug designed to

yield under lateral deformation and to dissipate supplemental energy.

Discussed in next section.


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Laminated elastomeric bearings in a bridge



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400 laminated elastomeric bearings and

186 Taylor viscous dampers with

displacement capacity of 600 mm.

San Bernardino Hospital, California, 1993



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Image T. Saito


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Elastomeric Bearings for Sakhalin I Orlan Platform.

Tested at University at Buffalo.

Photos: Courtesy of M. Constantinou

Gravity Test Shear Test


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5. Laminated Rubber Bearings Force-Displacement relationship for various

types of elastomeric bearings

Shear strain defined as lateral displacement/total height of rubber

(From Thompson et al. 2000)

High Damping Rubber

Lead Rubber

Low Damping

Scragging


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Full-Scale Isolated Bridge Testing

Video


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Full-Scale Isolated Bridge Testing

-1.5 -1 -0.5 0 0.5 1 1.5-4

-3

-2

-1

0

1

2

3

4

Uy (in)

F (kip

)

Force-Displacement Hysteresis - Side A

LC6 vs D5

-5 -4 -3 -2 -1 0 1 2 3 4 5-4

-3

-2

-1

0

1

2

3

4

Uy (in)

F (

kip

)

Force-Displacement Hysteresis-Side B

LC2 vs D9


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5. Laminated Rubber Bearings Disadvantage of Laminated Rubber Bearings:

Relatively low damping provided by the rubber.

High damping rubbers: Developed for laminated rubber bearings.

Used mainly in Japan (Pan et al. 2004).

Significant more energy dissipation than low damping rubbers.

20% damping at shear strains of 300%.

More susceptible to heat related property changes during cyclic loading and to aging effects.

Increases complexity to predict short and long term properties for bounding analysis.

Isolator damping external components: Lead plug inserted in center of the bearing (lead-rubber bearings).

External supplemental damping by hysteretic or viscous dampers.


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Lead-rubber bearing composed of a laminated-rubber bearing with a cylindrical lead plug inserted in it center.

Lead plug introduced to increase damping by hysteretic shear deformations of the lead.



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Reasons to use lead for central plug:

At room temperature, lead behaves as elastic-plastic solid.

Yields in shear at low stress of about 10 MPa.

Lead is hot-worked at room temperature.

Properties continuously restored when cycled in inelastic range.

Very good fatigue resistance properties.

Lead commonly available since used in batteries at purity level of more than 99.9%


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Properties of Lead-Rubber Bearings


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6. Lead-rubber Bearings SRMD Testing Machine, UC-San Diego

DIS LR Bearing, Vertical Load = 558 kips, Displacement = 22 in, velocity = 60 in/s


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6. Lead-rubber Bearings SRMD Testing Machine, UC-San Diego

DIS LR Bearing, 400% strain


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6. Lead-rubber Bearings Failure Test, NIED, Tsukuba, Japan


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7. Friction Pendulum System General Description

FPS manufactured by Earthquake Protection Systems (EPS), Richmond, California.

Friction-type sliding bearing using gravity as restoring force.


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General Description

Articulated friction slider traveling on spherical concave lining surface.


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Slider on concave surface to provide re-centering capabilities through gravity Friction Pendulum bearing shown below

Typically PTFE on polished stainless steel surface


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Salkhalin II offshore gas platform bearings.

Largest seismic isolators.

700mm displacement.

87,400kN vertical load.

Full-scale testing

Reduced scale dynamic testing (load of up to

13,000kN, velocity of 1m/sec).



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FPS Isolator, Vertical Load = 3490 kips, Displacement = 29 in, velocity = 53 in/s


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New International Terminal

San Francisco International Airport


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HAYWARD CITY HALL, CALIFORNIA

NEXT TO HAYWARD FAULT

53 FP BEARINGS AND 15 NONLINEAR

VISCOUS DAMPING DEVICES

600 mm DISPLACEMENT CAPACITY



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KODIAK, ALASKA

COLD TEMPERATURE APPLICATION

-40 DEG TEMPERATURE, STRONG WIND



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Properties of Frictionless Pendulum System


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7. Friction Pendulum SystemShake table tests of a full-scale 5-story steel moment frame building (PI: K. Ryan, Reno; S. Mahin, Berkeley; G. Mosqueda, San Diego)

triple friction pendulum isolators

lead rubber bearing/cross linear slider

Fixed base

o Simulations designed to impose large displacement demands in isolation systems

o Simulations both with and without vertical component of ground motion

o 4th and 5th floor included nonstructural systems


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E-Defense Experiments: 5 story steel moment frame

Measured response

7. Friction Pendulum SystemLe

vel

Peak Acceleration Profile

Peak Acc. (g)

50 60 70 80 90 100

-0.5

0

0.5

-0.48446

-0.11864

0.14598

Fixed Base

TPB Isolated

LRB Isolated

50 60 70 80 90 100

-0.5

0

0.50.5844

0.14362

-0.23067

Base Shear Coefficient

X-d

ire

ctio

nY

-dir

ect

ion

Time (sec)


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