Chapter 1Introduction

CIE 626 - Structural ControlChapter 1 - Introduction

CIE 626 Structural ControlChapter 1 - Introduction

CONTENT

1. Fundamental Concepts2 Brief History of Supplemental Damping2. Brief History of Supplemental Damping

and Base Isolation Systems3 Categories of Supplemental Damping and3. Categories of Supplemental Damping and

Seismic Isolation Systems

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1. Fundamental Concepts

• Basic performance objective of “conventional” seismic design: life safetyg y

• Life safety performance objective not sufficient for important structuressufficient for important structures

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

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O.K.

NotO.K.

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1. Fundamental Concepts

• Supplemental Damping Systems:– Special devices – “mechanical dampers”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:If all seismic energy dissipated mechanically:

no damage

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1. Fundamental Concepts• Seismic Isolation Systems:

– Installation of “isolators” beneath supporting points of the structure

– Buildings: isolators located between superstructure and foundationfoundation

– 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

damageCIE 626 - Structural Control

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damage

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1. Fundamental Concepts• Components of Seismic Isolation Systems:

– IsolatorIsolator• Lateral stiffness much less than superstructure• Increase effective period of vibrationp• 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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1. Fundamental Concepts• Illustrative Example

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Point A: original portal frame, T = 1.0 secPoint B: portal frame with added viscous damper, = 20%, T = 1.0 secPoint C: portal frame with added hysteretic damper, = 20%, T = 0.55 secPoint D: portal with added bracing system, = 5%, T = 0.55 sec

CIE 626 - Structural ControlChapter 1 - Introduction

p g y Point E: base isolated portal frame, = 5%, T = 2.0 secPoint F: base isolated portal frame, = 20%, T = 2.0 sec 9

1. Fundamental ConceptsIt is a combination of period shift and added energ dissipationIt 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 undergoesNote: Behavior and analysis more complex if structure undergoesinelastic deformations

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2. Brief History of Supplemental Damping and Seismic Isolation Systemsand Seismic Isolation Systems

• Seismic Isolation Systems– 1885: John Milne: built a base isolated house in Japan1885: John Milne: built a base isolated house in Japan– 1909: J.A. Calantarients (MD) filed a patent in

England for lubricated “free joints” on a layer of fine g j ymaterial

– 1969: first rubber isolation of 3-story reinforced t l t h l b ildi i Sk jconcrete elementary school building in Skopje,

Yugoslavia– 1970 – present: wide spread worldwide applications1970 present: wide spread worldwide applications

(elastomeric bearings, high damping rubber bearings, lead-rubber bearings, metallic bearings, lead-extrusion b i d f i i d l b i )

CIE 626 - Structural ControlChapter 1 - Introduction

bearings and friction pendulum bearings)11

2. Brief History of Supplemental Damping and Seismic Isolation Systemsand Seismic Isolation Systems

• Seismic Isolation Systems

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LEAD-RUBBER BEARINGS

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FRICTION PENDULUMFRICTION PENDULUM

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New International TerminalSan Francisco International AirportSan Francisco International Airport

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CALTRANS TOLL BRIDGES RETROFIT PROJECTRETROFIT PROJECT

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1995Kobe Earthquake

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2. Brief History of Supplemental Damping and Seismic Isolation Systemsand Seismic Isolation Systems

• Supplemental Damping SystemsDevelopment more recent than base isolation systems– Development more recent than base isolation systems

– 1956: Pioneering work by G. Housner on energy in earthquake engineering– 1969-1972: Development of early metallic dampers in New Zealand and

JapanJapan– 1981: First application of hysteretic dampers on South Rangitikei viaduct in

New Zealand– 1980-83: Development of friction dampers in Canada1980 83: Development of friction dampers in Canada– 1987: First application of friction dampers at the Concordia University

Library in Montreal, Canada– 1990-1995: Development of fluid type viscous dampers at the University at p yp p y

Buffalo– 1995: First application of fluid dampers in Pacific Bell North Area

Operations Center in Sacramento, California

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• South Rangitikei River Railroad Bridge, New Zealand, built in 1981g , ,

• Piers: 70 m tall, six spans prestressed concrete hollow-box girder, overall

315span: 315 m • Rocking of piers combined with

energy dissipation devices (torsional gy p (dampers)

• Gravity provides self-centering force

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WELLS FARGO BANK BUILDING SAN FRANCISCOSAN FRANCISCO

• Two-story non-ductile concrete frame

• Constructed in 1967• Damaged during the 1989 g g

Loma Prieta Earthquake• Voluntary upgrade with

chevron braces and ADAS devices

• Conventional retrofit rejected because of foundation work

• Seven ADAS devices, each with a yield force of 150 kips

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Boeing Plant, Seattle, Washington

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Reservoir, Sacramento, California

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WOODLAND HOTEL, CA • Four-story reinforced

concrete/shear wall buildingbuilding

• Constructed in 192716 T l D• 16 Taylor Dampers

• Capacity of each damper = 100 kipsdamper = 100 kips

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3. Categories of Supplemental Damping and Seismic Isolation Systemsand Seismic Isolation Systems

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Questions/Discussions

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