Implementation of Base Isolation in Retrofit Applications · Forell / Elsesser Engineers, Inc....

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100th Anniversary Earthquake Conference

Commemorating the 1906 San Francisco Earthquake

Implementation of Base Isolation Implementation of Base Isolation in Retrofit Applicationsin Retrofit Applications

Presented bySimin Naaseh, SE, Principal Mason Walters, SE, Principal

Forell/Elsesser Engineers, Inc.April 17th, 2006

Forell / Elsesser Engineers, Inc.

Impetus for Base Isolation of Existing Buildings

Enhanced seismic protectionEnhanced seismic protection

Reduced extent of Reduced extent of superstructure retrofitsuperstructure retrofit

Protection of historic fabricProtection of historic fabric

Protection of valuable contentsProtection of valuable contents

Cost advantageCost advantage

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Technical Issues Unique to Base Isolation Retrofit

Isolation system is designed Isolation system is designed to meet certain thresholdsto meet certain thresholds

Limited existing structure Limited existing structure capacitycapacity

Unique dynamic response of Unique dynamic response of the structurethe structure

Limits on floor accelerationLimits on floor acceleration

Limits on moat dimensionLimits on moat dimension

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Base Isolation RetrofitPlanning and Design Challenges

Accommodating the isolator Accommodating the isolator spacespace

Accommodating the moatAccommodating the moat

Retrofitting the building Retrofitting the building appendages to accommodate appendages to accommodate free movement free movement

Retrofitting stairs and elevators Retrofitting stairs and elevators to accommodate large to accommodate large displacementsdisplacements

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Base Isolation RetrofitConstruction Challenges

Minimize building vulnerability Minimize building vulnerability during constructionduring construction

Minimize impact on brittle Minimize impact on brittle elementselements

Isolator installation sequenceIsolator installation sequence

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Seismic Retrofit of San Francisco City Hall

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Historic Rotunda

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Major Earthquake Response Issues

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Fixed Base Response - Shear Walls

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Major Earthquake Response Issues

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Fixed Base Response

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Base Isolated Response

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Sequence of Construction

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New Foundation

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New Foundation

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New Foundation

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Column Jacking

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Column Cutting

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Installation of Base Isolators

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Perimeter Shoring

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Perimeter Side Beams

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Perimeter Side Beams

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Installed Isolators at Perimeter

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New Ground Floor

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New Shear Walls

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Berkeley Civic Center

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C

Isolators at Basement

Section Looking West

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C

Basement Wall / Jacking Pier Construction Sequence

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C

Column Jacking / Isolator Installation Construction Sequence

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Existing Condition

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Install Foundation Reinforcing

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New Foundation Built

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Install Formwork for Jacking Piers Around Existing Columns

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Jacking Pier Construction

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Jacking Pier Built

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Temporary Jacks Installed

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Existing Column Cut

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Existing Column Cut

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Isolator Installed

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Isolator Installed

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Isolator Locking Plates Installed

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Steel Bracing Installed

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Locking Plates Removed

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Isolators Installed

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Base Isolation Response at Perimeter Wall

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Design an ConstructionProblems and Solutions

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Construction Problems and Solutions

Sequence of operationsSequence of operations

Symmetry and balanceSymmetry and balance

Cutting and jackingCutting and jacking

PreloadingPreloading

Temporary lateral strengthTemporary lateral strength

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Structure Types

Unreinforced Unreinforced masonry bearing wallmasonry bearing wall

Steel / masonry infillSteel / masonry infill

Reinforced concreteReinforced concrete

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Example: Unreinforced Masonry Bearing Wall Building

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Salt Lake City and County Building

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Bearing Wall Sequence

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Bearing Wall Sequence

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Isolator Installed at Perimeter

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Example: Steel Framed Building

with Masonry Infill

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Oakland City Hall

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Identification of Existing Building Properties

Archaic materials and infill systemsArchaic materials and infill systems

Structure’s Modal frequenciesStructure’s Modal frequencies

Forced/Ambient Vibration TestsForced/Ambient Vibration Tests

Historic DataHistoric Data

Old Old AccelerogramsAccelerograms

Masonry infill example Masonry infill example

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Identification of Existing Building Properties

Tests of Existing MasonryTests of Existing Masonry

InIn--situ cyclic testssitu cyclic tests

Obtain shear stressObtain shear stress--strain relation, Gstrain relation, G

Obtain diagonal cracking strain,Obtain diagonal cracking strain, ggcrcr

Use G for elastic modeling of structureUse G for elastic modeling of structure

Use Use ggcrcr to determine the limits of to determine the limits of acceptable interacceptable inter--story driftstory drift

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In-Situ Masonry Test

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Stress Versus Deflection

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Local Wall Model

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ETABS Model

(Non-Linear ANSR)

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Jacking of Existing Column

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Column Cutting

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Example: Reinforced Concrete

Frame Buildings

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Pasadena City Hall

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Building Section Showing Load Transfer

8

3

(E) Column

7

2

59

6

1(E) Footing (to be Removed)

1

(E) Wall

(E) Basement Grade

1 Shoring

2 Foundation

3

4

5

6

7

8

9

(E) Wall

Moat Cover

4

Grade Beam & S.O.G. Friction Pendulum Isolator PT Threadbar(Clamping Reinforcing)

Concrete Pedestal

Temporary Shoring

PT Conc. Transfer Girder

Concrete Slab

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Installation of Isolators

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Utah State Capital Building

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Overall Basement

Plan

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Big Idea

Rotunda base must be isolated with Rotunda base must be isolated with remainder of buildingremainder of building

Main problem Main problem –– getting isolators “beneath” getting isolators “beneath” rotunda footingrotunda footing

“Below” and “Above” approaches studied“Below” and “Above” approaches studied

“Above” approach safer to build, requires “Above” approach safer to build, requires less excavationless excavation

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Big Idea

Existing concrete has relatively good Existing concrete has relatively good quality, strengthquality, strength

Maintain footing Maintain footing –– make it work as part of make it work as part of new transfer girdernew transfer girder

“Composite”“Composite”

Allow new transfer structure to span to Allow new transfer structure to span to isolators on new foundations (fig)isolators on new foundations (fig)

New foundation can be built ahead of New foundation can be built ahead of transfer transfer –– outside existing footingoutside existing footing

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Existing Footing

How to Achieve Composite Action and Transfer Load?

Stress Girders

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Locate and Mark PT Ducts on Flange

How to Achieve Composite Action and Transfer Load?

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Rotunda Footing

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100th Anniversary Earthquake Conference

Commemorating the 1906 San Francisco Earthquake

Implementation of Base Isolation Implementation of Base Isolation in Retrofit Applicationsin Retrofit Applications

Presented bySimin Naaseh, SE, Principal Mason Walters, SE, Principal

Forell/Elsesser Engineers, Inc.April 17th, 2006