National Park Service – Base Isolation and Blast Loads

Base Isolation Technology and

Blast Loading

Dr. Ronald L. Mayes – SGH Dr. Eve Hinman – HCE

National Park Service – Base Isolation and Blast Loads

Engineering Design Issues

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

National Park Service – Base Isolation and Blast Loads

Innovations in Earthquake Engineering

Base Isolation Fiber Wrap Dampers Steel moment frame solutions

Redundancy – helps with progressive collapse

Capacity design principles

In general what’s good for earthquake design helps resist blast loads

National Park Service – Base Isolation and Blast Loads

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!!

National Park Service – Base Isolation and Blast Loads

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!

National Park Service – Base Isolation and Blast Loads

Current Design CodesExpected 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.”

National Park Service – Base Isolation and Blast Loads

Performance Based Design (PBD)

Owner chooses desired performance Reduce business interruption Reduce damage costs

National Park Service – Base Isolation and Blast Loads

Performance Based Design Documents

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

National Park Service – Base Isolation and Blast Loads

Operational(Negligible Damage)

Immediate Occupancy(Light Damage)

Life Safety(Moderate Damage)

Collapse Prevention(Severe Damage)

Collapse(Complete Damage)

Damage States & Performance Level Thresholds

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

Base IsolationHow It Works

National Park Service – Base Isolation and Blast Loads

Isolated Structure Conventional Structure

National Park Service – Base Isolation and Blast Loads

Ground Forces are amplified

by a factor of 3 to 4 at the

roof.

Conventional Structure

National Park Service – Base Isolation and Blast Loads

Forces reduced by 3 to 6 across the isolators

Forces reduced by 8 to 12 at the roof

Isolated Structure

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

Seismic Isolator

Cover Rubber

Energy Dissipation Core

Steel Reinforcing Plates

Internal Rubber Layers

Bottom Mounting Plate

(Top Mounting Plate Not Shown)

National Park Service – Base Isolation and Blast Loads

Friction Pendulum Bearing

SECTION

STAINLESS STEELCONCAVE SURFACE

SELF LUBRICATINGCOMPOSITE LINER

ARTICULATINGSLIDER

PLATECONCAVE

HOUSINGPLATE

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

US APPLICATIONS

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

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

National Park Service – Base Isolation and Blast Loads

San Francisco Airport International Terminal

World’s Largest Isolated Building

National Park Service – Base Isolation and Blast Loads

Benefits of Seismic Isolation Retrofit

Work maybe Confined to

Basement

Building Can Continue to be

Occupied

Often the Most Economic

Solution

National Park Service – Base Isolation and Blast Loads

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

Threat Definition ISC Security Criteria High Protection

Facility 500 lb weapon

curbside 20 foot standoff

National Park Service – Base Isolation and Blast Loads

Blast Base Shear

US Department of State standards

Seismic Base Shear Governs

National Park Service – Base Isolation and Blast Loads

Air-Blast Effects Direct Air-blast Effects

Local Global

Collateral Effects Progressive Collapse

Time Regime Seconds vs.

Milliseconds

National Park Service – Base Isolation and Blast Loads

Blast Base Shear is a function of:

Total Impulse Period of Vibration Displacement

Ductility

National Park Service – Base Isolation and Blast Loads

Total Impulse Calculation Weapon Size Standoff Building Dimensions CONWEP

National Park Service – Base Isolation and Blast Loads

Isolated Structure Conventional Structure

Force

Time

Impulse Load I = Force x duration

Velocity V = I / M

Kinetic Energy = ½ M V2

National Park Service – Base Isolation and Blast Loads

Kinetic Energy = Strain Energy = Area under F – D Curve

Force

Deflection

National Park Service – Base Isolation and Blast Loads

Force

Deflection

Fy =___2 I___

2T (2 -1)0.5

Fy

National Park Service – Base Isolation and Blast Loads

Yield Level Fy = 0.03W to 0.07W

Yield Displacement = 0 to 0.5 inches

Force

Deflection

Fy

Dy

National Park Service – Base Isolation and Blast Loads

Maximum Displacement = 20 to 36 inches

Maximum Force = 0.15W to 0.25W

Force

DeflectionDmax

Fmax

National Park Service – Base Isolation and Blast Loads

Salt Lake City and County Building

High 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

National Park Service – Base Isolation and Blast Loads

Oakland City Hall

High 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

National Park Service – Base Isolation and Blast Loads

San Francisco City Hall

High 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

National Park Service – Base Isolation and Blast Loads

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.

National Park Service – Base Isolation and Blast Loads

Does Isolation Work?

National Park Service – Base Isolation and Blast Loads

Isolated

National Park Service – Base Isolation and Blast Loads

Conventional

National Park Service – Base Isolation and Blast Loads

Kobe Earthquake Force

National Park Service – Base Isolation and Blast Loads

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

National Park Service – Base Isolation and Blast Loads

Isolated

National Park Service – Base Isolation and Blast Loads

Conventional

National Park Service – Base Isolation and Blast Loads

Northridge Earthquake Force