Transcript Case Study

Approaches to Historic Bridge Rehabilitation
Case Study #2
Holmes Street Bridge, No. 4175
(Deck Truss)
Shakopee, Minnesota
Bob Frame
Mead & Hunt, Inc.
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Case study #2
Holmes Street Bridge No. 4175
 Shakopee, Minnesota
 Built to carry MN trunk highway over the Minnesota River,
tributary to Mississippi
 Pedestrian use since 2005
 Deck truss
 Built 1927
 Structure length: 645 feet
 4 main river spans: Warren truss, with 3 truss lines
 4 approach spans (2 north, 2 south): cast-in-place concrete
beams
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Bridge 4175 Rehab
 Project: to restore and convert to pedestrian use
 Rehab in process 2010-2011
 Client/Owner: Mn/DOT
 Engineer: HDR, Inc.
 Contractor: Kramer Bros.
 Section 106 rehab guidance: Mead & Hunt, Inc.
2005 - Before rehab
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2010 - During rehab
Issue 1 - Repair gusset-plate connections &
replace lower chord members
Left: Typical gusset plate in good condition, upper
and center of trusses.
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Right: Typical gusset plate in poor condition, located
below drains.
 Lower chord members & gusset plates in
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serious-to-critical condition
Gusset plate with retrofit; up to 100% section
loss in some plates.
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Buckled gusset plate between diagonal &
vertical members
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How Significant Issue Was Resolved
 First, strong-back system used to relieve stress on truss connections
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Rivets were removed.
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• Rivets replaced with bolts
• Old bearing pins replaced
• Lower chord members replaced.
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Issue 2 – Repair historic concrete
 On concrete approach spans &
abutments
 Delamination, spalling, graffiti
Beams to be repaired
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Sidewalk brackets to be replaced
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How Significant Issue Was Resolved
 Shotcrete used for repair patches and to
replicate missing features
 Test repairs to check replication of
architectural shapes
 Test panels to compare color & surface
texture treatment
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How Significant Issue Was Resolved
Sculpting architectural details
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Applying shotcrete to repair area
Replicating concrete sidewalk brackets
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After initial concrete demolition
Building formwork
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Removing forms
Contractor demonstrating graffiti & paint removal
Left:
•
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Using water – less effective
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Right:
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Using micro-abrasive blast – more
effective
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Black Diamond product used
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How was Section 106 handled
 Issue: all rehab to be compliant with Secretary of the
Interior’s Standards
 Steel repairs were considered compliant
 Concrete repairs considered compliant
 Shotcrete use approved by SHPO
 Micro-abrasive blast approved by SHPO
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How was Section 4(f) handled
 No 4(f) issues
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Lessons Learned/Conclusions
 Lifting truss allows repair/replacement of gusset plate
connections & lower chord members
 Shotcrete to repair & match adjacent historic concrete
 Sculpted to replicate details
 Concrete stain for color
 Micro-abrasive blast for texture
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