Base Isolation Technology and Blast Loading Dr. Ronald L. Mayes SGH Dr. Eve Hinman HCE

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Base Isolation Technology and Blast
LoadingDr. Ronald L. Mayes SGH Dr. Eve
Hinman HCE
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Engineering Design Issues

• Earthquakes
• Wind
• Blast / Progressive collapse
• Green Engineering
• Sensitivity to Historic Preservation Issues

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Innovations in Earthquake Engineering

• Base Isolation
• Fiber Wrap
• Dampers
• Steel moment frame solutions
• Redundancy helps with progressive collapse
• Capacity design principles
• In general whats good for earthquake design
  helps resist blast loads

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Earthquakes can be Catastrophic and Very
Expensive

• Loma Prieta 7 Billion
• 450 Million per Second
• Northridge - 30 Billion
• 2 billion per second!
• Kobe - 150 - 200 Billion
• 7.5 billion per second!!

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Duration is Magnitude Dependent

• 1906 San Francisco 8.3 1 min.
• 1964 Alaska 8.4 4 min.
• 1989 Loma Prieta 7.1 15 sec.
• 1994 Northridge 6.7 12 sec.
• 1995 Kobe 7.1 15 sec.
• Loma Prieta, Northridge and Kobe
• were not the Big Ones!

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Current Design Codes Expected Performance
These design requirements primarily are intended
to safeguard against major failures and loss of
life, NOT to limit damage, maintain functions, or
provide for easy repairs.
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Performance Based Design (PBD)

• Owner chooses desired performance
• Reduce business interruption
• Reduce damage costs

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Performance Based Design Documents

• Vision 2000
• FEMA 356/273
• ATC 40
• FEMA 310

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Base Isolation Technology

• One of the most significant developments in
  earthquake engineering in the past 35 years
• It provides the design profession the ability to
  design a building that is operational after a
  major earthquake

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The Goals of Base Isolation

• Protection of Life Current Code
• Additional Benefits of Isolation
• Protection of Building Frame
• Protection of Non-Structural Components and
  Contents
• Protection of Processes and Function
• Provide for an operational facility after the
  earthquake

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Base IsolationHow It Works
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Isolated Structure
Conventional Structure
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• Ground Forces are amplified by a factor of 3 to 4
  at the roof.

Conventional Structure
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• Forces reduced by 3 to 6 across the isolators
• Forces reduced by 8 to 12 at the roof

Isolated Structure
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• During a Richter 8.0 Earthquake a Seismically
  Isolated Building Will Behave as if it Were
  Experiencing a 5.5 Earthquake

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Seismic Isolator
(Top Mounting Plate Not Shown)
Energy Dissipation Core
Steel Reinforcing Plates
Cover Rubber
Internal Rubber Layers
Bottom Mounting Plate
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Friction Pendulum Bearing
STAINLESS STEEL CONCAVE SURFACE
SECTION
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Applications of Base Isolation

• 1st application in New Zealand in 1974
• 1st US application in 1984
• 1st Japanese application in 1985
• US - 80 buildings and 150 bridges
• Japan - 1000 buildings and 500 bridges

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US APPLICATIONS

• 55 Government
• 45 Private sector
• 55 New Buildings
• 45 Retrofit of Existing Buildings

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US APPLICATIONS

• 12 Historic building retrofits
• 8 Hospitals
• 8 Emergency Operation Centers
• 7 Manufacturing Facilities
• 7 Computer Centers
• 6 University Buildings
• 6 Court Houses / Police Buildings
• 3 Laboratories
• 3 Library / Museums
• 2 Residences
• 10 Miscellaneous Tanks/Labs /Airports /Church
  etc

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San Francisco Airport International
Terminal Worlds Largest Isolated Building
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Benefits of Seismic Isolation Retrofit

• Work maybe Confined to Basement
• Building Can Continue to be Occupied
• Often the Most Economic Solution

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1994 Northridge Earthquake

• 31 Hospitals had significant damage
• 9 Hospitals partially or fully evacuated
• USC University Hospital the first isolated
  hospital suffered no damage at all
• Los Angeles County General Hospital less than 1
  mile from the USC isolated hospital had 389
  million in damage

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Base Isolation and Blast Loads

• Does the use of base isolation help or hurt
  the response of a building subjected to blast
  loads
• Global impact
• Local effects

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Threat Definition

• ISC Security Criteria
• High Protection Facility
• 500 lb weapon curbside
• 20 foot standoff

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Blast Base Shear

• US Department of State standards
• Seismic Base Shear Governs

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Air-Blast Effects

• Direct Air-blast Effects
• Local
• Global
• Collateral Effects
• Progressive Collapse
• Time Regime
• Seconds vs. Milliseconds

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Blast Base Shear is a function of

• Total Impulse
• Period of Vibration
• Displacement Ductility

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Total Impulse Calculation

• Weapon Size
• Standoff
• Building Dimensions
• CONWEP

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Isolated Structure
Conventional Structure
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Force
Impulse Load I Force x duration
Velocity V I / M Kinetic Energy ½ M V2

Time
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Force Deflection Curve of Isolator
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Kinetic Energy Strain Energy
Area under F D Curve
Force
Deflection
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Force
Fy
Deflection
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Yield Level Fy 0.03W to 0.07W Yield
Displacement 0 to 0.5 inches
Force
Fy
Deflection
Dy
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Maximum Displacement 20 to 36 inches Maximum
Force 0.15W to 0.25W
Force
Fmax
Deflection
Dmax
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Salt Lake City and County BuildingHigh Risk GSA
Building with 20 ft Standoff

• Impulse load is 360 kip-sec.
• Yield Level of the isolators is 3100 kips
• Isolators displace less than 1 inch
• For a 10 inch movement in the isolators the blast
  load could be 5 times greater

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Oakland City HallHigh Risk GSA Building with 20
ft Standoff

• Impulse load is 300 kip.-sec.
• Yield level of the isolators is 3060 kips
• Isolators displace less than 1 inch
• For a 10 inch movement in the isolators the blast
  load could be 6 times greater

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San Francisco City HallHigh Risk GSA Building
with 20 ft Standoff

• Impulse load is 480 kip.-sec.
• Yield level of isolators is 14,000 kips
• Isolators displace less than 1/4 inch
• For a 10 inch movement in the isolators the blast
  load could be 18 times greater

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Conclusions

• Base isolation provides the highest level of
  protection operational - after a major
  earthquake
• Base isolation has significant benefits for the
  earthquake protection of historic structures
• Base isolated buildings are capable of resisting
  GSA blast loads and their ability to move reduces
  the overall impact of the blast force on the
  building.

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Does Isolation Work?
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Isolated
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Conventional
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Kobe Earthquake Force
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1994 Northridge Earthquake

• 31 Hospitals had significant damage
• 9 Hospitals partially or fully evacuated
• USC University Hospital the first isolated
  hospital suffered no damage at all
• Los Angeles County General Hospital less than 1
  mile from the USC isolated hospital had 389
  million in damage

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Isolated
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Conventional
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Northridge Earthquake Force