Download - Seismic Isolation Bearings
D.S. Brown Company Seismic Isolation Bearings
Seismic Isolation Bearings1. Basic Theory2. Isolation Devices
Benefits of Seismic Isolation3. Compared to standard
design methods4. Comparison between
LRB and other devices
Overview
Seismic isolation technology involves:Placing the isolators between the superstructure and substructures in place of regular bearings
Basic Theory
Seismic isolation technology involves:Insertion of devices (isolators) that provide:
• Period shift – by means of low lateral stiffness bearings
• Added damping – hysteretic, friction, viscous
• Displacement capacity – by means of rubber or slidingAll in one, self-contained, maintenance-free unitReplacement not needed after seismic event(s)
Basic Theory
Increasing Period of Vibration
Acce
lera
tion
Typical Fixed-Base Structure
Typical Isolated Structure
Basic TheoryA. Shifting the fundamental period of the structure
Idealized Displacement Response Spectrum
Increasing Period of Vibration
Disp
lace
men
t
Typical Fixed-Base Structure
Typical Isolated Structure
With Added Damping
Idealized Displacement Response Spectrum
Basic TheoryB. Adding damping to control displacements
– Maintenance-Free– Good for Life-Span of Structure– No need for Replacement after
Earthquake– Proven Performance (shaking-
table + real earthquakes)
Description of the TechnologyMost Commonly used Isolator System:Elastomeric Isolators with Lead CoresAdvantages
Applications• Function Critical Structures
- Lifeline bridges, hospitals, emergency and first response structures
• Critical Operational Structures- Data storage centers- Utilities- Communication towers- Military or scientific structures- Piers
• Historical or High-Value Structures- Historical bridges and buildings- Museums, mints, national treasures- Petroleum, gas, chemical structures
In the USA and worldwide, LRB are most often selected
D.S. Brown:• Over 80 Bridge projects since 1995• Thousands of Isolators• Fabricating and Testing isolators since 1986• Design, Fabrication and Testing since 1995
LRB has the Longest Track Record worldwideIn earthquakes, structures with LRB performed very well
Where does D.S. Brown fit in?
Typical Configuration
Typical Configuration
Typical Configuration
Typical Configuration
Fabricating Multiple Isolators at Once
Finished Lead Rubber Isolators
A. Why try to reduce seismic forces to the substructures?
• Reduce or eliminate strengthening during retrofit
• Reduce substructure dimensions
• Reduce footing and pile requirements
• All of the above
Each of these benefits will SAVE MONEY and TIME.
Reduce construction time and avoid traffic restrictions.
Benefits of Seismic Isolation
B. Why redistribute seismic and service loads in bridges?
• Seismic loads can be sent to strongest substructures
• Lateral service loads can be redistributed
This SAVES MONEY and construction TIME. Use existing
capacity and send more force to stronger locations in order
to eliminate or minimize retrofit of weaker substructures.
Benefits of Seismic Isolation
C. Why deal with something new when we can design a code compliant bridge without isolators?
Because isolators actually reduce substructure forces whereas traditional design methods do not. An isolated structure will perform better because the isolation bearings will:
• Reduce or eliminate inelastic deformation
• Reduce damage from earthquake
• Permit immediate use after earthquake
Reduce or eliminate repair COSTS and TIME
Benefits of Seismic Isolation
Summary:
• Can reduce the cost of construction
• Avoid retrofit and reduce traffic disruptions
• Eliminate damage and reduce losses from earthquakes
Uninterrupted operation after an earthquake
Revenue from bridge tolls
Use by emergency vehicles
Use by construction companies to reach affected areas
Benefits of Seismic Isolation
Golden Gate Bridge, CA South ApproachLRB Isolation Bearings
Lead-Rubber Isolators are “special” Elastomeric Bearings• Design approach was very different from Methods A & B• AASHTO LRFD design is now similar to AASHTO Isolation GS• Detailed design calculations required for each isolator• Shear testing is done on each job, typically 100% tested
As a result, isolators have:• Higher capacity for axial loads and shear displacement• Higher cost
How are Isolators Different from “Bearings”?
Q.C. Test: Combined Compression & Shear
Dynamic Testing in Compression & Shear
Spectrum of Isolation ProjectsVariables include: Axial Load, Seismic Displacement, Plan Dimensions, Height of Isolators, Economy
LRB is Suitable and Economical for Most Projects
Extremely High LoadVery Large DisplacementSevere Height LimitationVery Low Stiffness
Extremely Small LoadVery Large DisplacementVery Low StiffnessSevere Height Limits
Applicability of LRB
Advantages of LRB Isolators over Other Systems
HISTORYSIMPLICITYRELIABILITYTOLERANCE OF IMPERFECTIONS• Long History based on Steel-Laminated Bearings• Similar Materials (NR, shims) as Steel Laminated• First Isolation Systems in US were LRB & HDR• Proven Performance in Actual Earthquakes
How does LRB compare to other systems?
1978
Lead
-Rub
ber Is
olator
Paten
ted in
US
1985
DIS L
icens
ed to
sell L
RB in
US
Firs
t Isola
ted B
ridge
in U
S (LR
B)
Fi
rst Is
olated
Buil
ding i
n US (
HDR)
“Erad
iquak
e” D
evice
Paten
ted
1986 1987
Frict
ion Pe
ndulu
m Paten
ted
Approx. 300 Isolated Structures in USAApprox. 2000 Structures Isolated Worldwide
Present1995
Kobe
Earth
quak
e
General Timeline of Seismic Isolation
• No Wear or Leakage Concerns• No Moving Parts• No Maintenance or Replacement Parts Required• Protected on All Sides by ½” Integral Cover Rubber
How does LRB compare to other systems?Advantages of LRB Isolators over Other Systems
HISTORYSIMPLICITYRELIABILITYTOLERANCE OF IMPERFECTIONS
• No Need to Replace or Repair after an Earthquake• Isolator Properties are Unchanged after Many Cycles
How does LRB compare to other systems?Advantages of LRB Isolators over Other Systems
HISTORYSIMPLICITYRELIABILITYTOLERANCE OF IMPERFECTIONS
Direction 1
• Installation the Same as an Elastomeric Bearing• Sacrificial Cover Rubber• Extra Capacity for Load, Rotation, Displacement• Will Support Axial Load after “Failure”
How does LRB compare to other systems?Advantages of LRB Isolators over Other Systems
HISTORYSIMPLICITYRELIABILITYTOLERANCE OF IMPERFECTIONS
Tolerance for Imperfections: Example
Tolerance for Imperfections: ExampleAs Installed by Contractor & Opened to Traffic
After Placing Grout
• The Contractor had already removed jacks, falsework, etc.
• The Owner wanted to know if the Isolators are OK
D.S. Brown needed to find out how will they perform under axial and shear loads.
Tolerance for Imperfections: Example
DSB fabricated 2 identical isolators and tested them:• In the un-deformed state, and• After deforming the masonry plates as seen in the bridge
Tolerance for Imperfections: Example
This Damage Caused No Appreciable Change in Performance
-100
-75
-50
-25
0
25
50
75
100
-3 -2 -1 0 1 2 3
Shear Displacement (inches)
Shea
r Fo
rce
(kip
s)
Prior to Deformation of Masonry Plate
After Deformation of Masonry Plate
Corporate Office300 East Cherry StreetNorth Baltimore, OH
45872
Websitewww.dsbrown.com