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National Park Service – Base Isolation and Blast Loads

Prof. Dr. Zahid A. Siddiqi, UET, Lahore

Innovations in Earthquake EngineeringBase 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



Base Isolation TechnologyOne 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



The Goals of Base IsolationProtection of Life – Current Code

Additional Benefits of IsolationProtection of Building Frame

Protection of Non-Structural Components and Contents

Protection of Processes and Function

Provide for an operational facility after the earthquake



Base IsolationHow It Works



Isolated Structure Conventional Structure



Ground Forces are amplified

by a factor of 3 to 4 at the

roof.

Conventional Structure



Forces reduced by 3 to 6 across the isolators

Forces reduced by 8 to 12 at the roof

Isolated Structure



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



Seismic Isolator

Cover Rubber

Energy Dissipation Core

Steel Reinforcing Plates

Internal Rubber Layers

Bottom Mounting Plate

(Top Mounting Plate Not Shown)



Friction Pendulum Bearing

SECTION

STAINLESS STEELCONCAVE SURFACE

SELF LUBRICATINGCOMPOSITE LINER

ARTICULATINGSLIDER

PLATECONCAVE

HOUSINGPLATE

∆ m = 20 to 30 inchesFmax = 3 to 4 times Fy

∆el



Applications of Base Isolation1st 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



San Francisco Airport International TerminalWorld’s Largest Isolated Building


Prof. Dr. Zahid A. Siddiqi, UET, LahoreBenefits of Seismic Isolation Retrofit

Work maybe Confined to Basement

Building Can Continue to be Occupied

Often the Most Economic Solution



Base Isolation and Blast LoadsDoes the use of base isolation help or hurt the response of a building subjected to blast loads

Global impact

Local effects



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.



Does Isolation Work?



Isolated



Conventional



Kobe Earthquake Force



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



Isolated



Conventional



Northridge Earthquake Force

Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea


M

gx&&

1x

µ

ASEISMIC BASE ISOLATION SYSTEMS

1. Pure Friction (PF) System1. Pure Friction (PF) System

the simplest devicethe simplest devicelimits a maximum acceleration transmitted from the limits a maximum acceleration transmitted from the substructuresubstructuremay have an excessive defection or a residualmay have an excessive defection or a residualdeformationdeformationmay be used economically in the simple or smallmay be used economically in the simple or small--scale structurescale structure


Prof. Dr. Zahid A. Siddiqi, UET, LahoreAseismic Base Isolation Systems

RubberInner steel plate

Outer steel plateProtective rubber

Flange

gx&&

1x

M

K

C

2. Rubber Bearing (RB) System2. Rubber Bearing (RB) System

widely studied and used over the world widely studied and used over the world consists of alternating layers of rubber and steel plateconsists of alternating layers of rubber and steel plateparallel action of spring and dashpotparallel action of spring and dashpotmainly shifts natural period of the isolated structuremainly shifts natural period of the isolated structure



3. Lead Rubber Bearing (LRB) System3. Lead Rubber Bearing (LRB) System

widely studied and used over the worldwidely studied and used over the worldadditional energy dissipation by a central lead coreadditional energy dissipation by a central lead corebilinear model of characteristic curve is usedbilinear model of characteristic curve is used

RubberInner steel plate

Outer steel plateProtective rubber

Flange

Central lead coregx&&

1x

M

Keff

Ceq

Aseismic Base Isolation Systems



4. Resilient Friction Base Isolation (R4. Resilient Friction Base Isolation (R--FBI) SystemFBI) System

parallel action of resiliency of rubber and frictionparallel action of resiliency of rubber and frictionof Teflon coated plateof Teflon coated platehas a recovering force by rubber after slidinghas a recovering force by rubber after sliding

gx&&

1x

µ

M

K

C

Cover plate

Central rubber core

Peripheral rubber core

Rubber cover

Connecting plate

Sliding ring




5. 5. ElectiriciteElectiricite De France (EDF) SystemDe France (EDF) System

consists of the elastomeric bearing and the frictionconsists of the elastomeric bearing and the frictionplate in seriesplate in seriesbehaves as a RB unit during a lowbehaves as a RB unit during a low--intensityintensityearthquakeearthquakemay have a residual deformation during a highmay have a residual deformation during a high--intensity earthquakeintensity earthquake

`

gx&&

2x

µM

K

C

1x

Reinforced neoprene pad

Friction plates

Stud anchor



Prof. Dr. Zahid A. Siddiqi, UET, LahoreSeismic Base Isolation



Time(sec)

Acc

eler

atio

n(g)

Frequency(Hz)

Mag

nitu

de

0 10 20 30 40-0.4

-0.2

0

0.2

0.4

El Centro

0 2 4 6 8 100

40

80

120

160

200

El Centro

0 1 2 3 4 50

0.5

1

1.5

2

2.5

Mexico City

0 15 30 45 60 75-0.2

-0.1

0

0.1

0.2

Mexico City

0 2 4 6 8 100

100

200

300

400

San Fernando

0 10 20 30 40-1.5

-1

-0.5

0

0.5

1

San Fernando

Sensitivity Analysis

SETTLEMENTS OF FOUNDATIONSSETTLEMENTS OF FOUNDATIONS

NO SETTLEMENT * TOTAL SETTLEMENT * DIFFERENTIAL SETTLEMENTNO SETTLEMENT * TOTAL SETTLEMENT * DIFFERENTIAL SETTLEMENTUniform settlement is usually of little consequence in a buildinUniform settlement is usually of little consequence in a building, but differential g, but differential

settlement can cause severe structural damagesettlement can cause severe structural damage

Tieback InstallationTieback Installation

Rotary Drill HoleRotary Drill Hole

Insert & Grout TendonsInsert & Grout Tendons

Tendons Stressed & AnchoredTendons Stressed & Anchored

BracingBracing

CrosslotCrosslot

RackersRackers

TiebacksTiebacks

Watertight Barrier WallsWatertight Barrier Walls

Keep Water OutKeep Water OutBarrier must reach an Barrier must reach an impervious strataimpervious strataTypesTypes–– Slurry WallsSlurry Walls–– Sheeting w/ pumpsSheeting w/ pumps

Must resist hydrostatic Must resist hydrostatic pressure pressure

Much Has Been Accomplished …Modern Ductile Details

• Initial Failure at ~0.6g

Courtesy of Caltrans

Older Brittle Details• Total Failure at ~0.2g• Retrofit Priority

Courtesy of Caltrans

Example: Applied Engr. ResearchExperimental Validation & Refinement of “Zipper Frame System” Concept

Courtesy of Prof. Roberto Leon, Georgia Tech.

Behavior controlled by brace buckling -system is unable to redistribute forcesefficiently

∆

VV

∆∆

V

Conventional Steel Braced Frame

∆∆∆

VVV

Zipper struts tie all brace-to-beam intersection points together and force all the compression braces to buckle simultaneously (Khatib, Mahin, Pister)

Zipper Frame

Weakens After First Yield

Strengthens After First Yield

YieldYield

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