Seismic Retrofit of Piers Supported on
Battered Piles Using
Lead-Rubber Bearings
Jeff Kilborn, MASCE, PE, SE
Robert Harn, MASCE, PE, SE
Yeliz Firat, PhD
Buildingonthe Past, Respectingthe Future
Presentation Overview
• Why Retrofit Batter Piles?
• Retrofit Case Study
– “Existing Pier” Response and Deficiencies
– Conventional Batter Pile Retrofit Scheme
– Lead Rubber Bearing (LRB) Retrofit Scheme
• Design Considerations
• Construction Process
• Advantages of LRB Retrofit Scheme
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Why Retrofit Batter Piles?
• Brittle Pile-to-Deck Connections
• Inadequate Geotechnical Capacities
• Inadequate Deck/Cap Reinforcement
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Case Study - “Existing Pier”
50’
(15.2m)
Deck
Pile cap
22’
6.7 m
A
Plumb piles
Batter piles
Section A-A
Under Strength
Brittle Connections
A
Partial Plan
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Seismic Response of Existing Pier
4500
Demand = 3900 kips
4000
CLE_5% Damping
CLE_10% Damping
3500
CLE_20% Damping
Base Shear (kips)
3000
Capacity Curve
2500
Ductility Limit
2000
1500
Capacity = 1300 kips
1000
500
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Spectral Displacement (inches)
1.
2.
3.
Initial Batter Pile System Fails
Less Stiff Plumb Pile System remains
Plumb Piles are Overwhelmed
1 Kip = 4.45 kN
1 Inch = 2.54 cm
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Conventional Batter Pile Retrofit Scheme
24 new battered pipe piles
driven through the existing
deck
12 new pile
caps
A
A
Decouple longitudinal
battered piles typical
Section A-A
Partial Plan
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Batter Pile Retrofit Response
4500
CLE_5% Damping
CLE_10% Damping
CLE_20% Damping
Capacity Curve_Transverse
Capacity Curve_Longitudinal
Strengthen batter
system Transverse
4000
3500
Base Shear (kips)
3000
Ductility Limit
2500
∆ = 5.5”
2000
1500
1000
Plumb pile system
longitudinal
500
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Spectral Displacement (in.)
Performance is Acceptable!
1 Kip = 4.45 kN
1 Inch = 2.54 cm
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7
Lead Rubber Bearing Elements
Lead Core
Rubber
Cover
Internal
Plate
Steel Shims
Between
Rubber
Layers
Flange
Plate
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8
LRB Retrofit Scheme
New LRBs mounted on new
subcaps supported on the
existing battered piles
A
Jacket/strengthen existing plumb
pile connection if required
Section A-A
A
Partial Plan
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LRB Retrofit Response
4500
CLE_5% Damping
CLE_10% Damping
CLE_20% Damping
Capacity Curve_ Example Pier
Capacity Curve_Pier w/ LRB
4000
3500
Base Shear (kips)
3000
2500
∆ = 4.3”
2000
Ductility Limit
1500
1000
500
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Spectral Displacement (inches)
Better Performance Than Conventional Scheme!
1 Kip = 4.45 kN
1 Inch = 2.54 cm
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10
Design Considerations
Pier Deck
Pile Cap
e1
e2
LRB
e2
Pile
e1
Sub Cap
Elevation
Plan
Section
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11
Construction Process
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12
Pile Shell Removal
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Stage 1 Pilecap Construction
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Shoring & Pile Cutoff
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Anchoring Pile Reinforcement
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Example of LRB Installation
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Advantages of LRB Retrofit Scheme
• Avoid Pile Driving
• Work Occurs Under Deck
• Bearings Remain Undamaged
• Cost Competitive
• Reliable & Designable Stiffness, Strength, and Damping
• Global Torsion Can Be Designed Away
• Forces Reduced for All Elements
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THANK YOU !!
Acknowledgements
• Bob Harn
• Yeliz Firat
Buildingonthe Past, Respectingthe Future