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Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
Seismic Retrofit of San Francisco City Hall
Forell / Elsesser Engineers, Inc.
Historic Rotunda
Forell / Elsesser Engineers, Inc.
Major Earthquake Response Issues
Forell / Elsesser Engineers, Inc.
Fixed Base Response - Shear Walls
Forell / Elsesser Engineers, Inc.
Major Earthquake Response Issues
Forell / Elsesser Engineers, Inc.
Fixed Base Response
Forell / Elsesser Engineers, Inc.
Base Isolated Response
Forell / Elsesser Engineers, Inc.
Sequence of Construction
Forell / Elsesser Engineers, Inc.
New Foundation
Forell / Elsesser Engineers, Inc.
New Foundation
Forell / Elsesser Engineers, Inc.
New Foundation
Forell / Elsesser Engineers, Inc.
Column Jacking
Forell / Elsesser Engineers, Inc.
Column Cutting
Forell / Elsesser Engineers, Inc.
Installation of Base Isolators
Forell / Elsesser Engineers, Inc.
Perimeter Shoring
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Perimeter Side Beams
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Perimeter Side Beams
Forell / Elsesser Engineers, Inc.
Installed Isolators at Perimeter
Forell / Elsesser Engineers, Inc.
New Ground Floor
Forell / Elsesser Engineers, Inc.
New Shear Walls
Forell / Elsesser Engineers, Inc.
Berkeley Civic Center
Forell / Elsesser Engineers, Inc.
C
Isolators at Basement
Section Looking West
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C
Basement Wall / Jacking Pier Construction Sequence
Forell / Elsesser Engineers, Inc.
C
Column Jacking / Isolator Installation Construction Sequence
Forell / Elsesser Engineers, Inc.
Existing Condition
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Install Foundation Reinforcing
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New Foundation Built
Forell / Elsesser Engineers, Inc.
Install Formwork for Jacking Piers Around Existing Columns
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Jacking Pier Construction
Forell / Elsesser Engineers, Inc.
Jacking Pier Built
Forell / Elsesser Engineers, Inc.
Temporary Jacks Installed
Forell / Elsesser Engineers, Inc.
Existing Column Cut
Forell / Elsesser Engineers, Inc.
Existing Column Cut
Forell / Elsesser Engineers, Inc.
Isolator Installed
Forell / Elsesser Engineers, Inc.
Isolator Installed
Forell / Elsesser Engineers, Inc.
Isolator Locking Plates Installed
Forell / Elsesser Engineers, Inc.
Steel Bracing Installed
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Locking Plates Removed
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Isolators Installed
Forell / Elsesser Engineers, Inc.
Base Isolation Response at Perimeter Wall
Forell / Elsesser Engineers, Inc.
Design an ConstructionProblems and Solutions
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
Structure Types
Unreinforced Unreinforced masonry bearing wallmasonry bearing wall
Steel / masonry infillSteel / masonry infill
Reinforced concreteReinforced concrete
Forell / Elsesser Engineers, Inc.
Example: Unreinforced Masonry Bearing Wall Building
Forell / Elsesser Engineers, Inc.
Salt Lake City and County Building
Forell / Elsesser Engineers, Inc.
Bearing Wall Sequence
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Bearing Wall Sequence
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Isolator Installed at Perimeter
Forell / Elsesser Engineers, Inc.
Example: Steel Framed Building
with Masonry Infill
Forell / Elsesser Engineers, Inc.
Oakland City Hall
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
In-Situ Masonry Test
Forell / Elsesser Engineers, Inc.
Stress Versus Deflection
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Local Wall Model
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ETABS Model
(Non-Linear ANSR)
Forell / Elsesser Engineers, Inc.
Forell / Elsesser Engineers, Inc.
Forell / Elsesser Engineers, Inc.
Jacking of Existing Column
Forell / Elsesser Engineers, Inc.
Column Cutting
Forell / Elsesser Engineers, Inc.
Example: Reinforced Concrete
Frame Buildings
Forell / Elsesser Engineers, Inc.
Pasadena City Hall
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
Installation of Isolators
Forell / Elsesser Engineers, Inc.
Utah State Capital Building
Forell / Elsesser Engineers, Inc.
Overall Basement
Plan
Forell / Elsesser Engineers, Inc.
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
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
Forell / Elsesser Engineers, Inc.
Existing Footing
How to Achieve Composite Action and Transfer Load?
Stress Girders
Forell / Elsesser Engineers, Inc.
Forell / Elsesser Engineers, Inc.
Locate and Mark PT Ducts on Flange
How to Achieve Composite Action and Transfer Load?
Forell / Elsesser Engineers, Inc.
Rotunda Footing
Forell / Elsesser Engineers, Inc.
Forell / Elsesser Engineers, Inc.
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
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