Approaches to Historic Bridge Rehabilitation Case Study #2 Holmes Street Bridge, No. 4175 (Deck Truss) Shakopee, Minnesota Bob Frame Mead & Hunt, Inc.

Holmes Street Bridge No. 4175 Case study #2 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

Bridge 4175 Rehab Case study #2 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 2010 - During rehab

Case study #2 Issue 1 - Repair gusset-plate connections & replace lower chord members Left: Typical gusset plate in good condition, upper and center of trusses. Right: Typical gusset plate in poor condition, located below drains.

Lower chord members & gusset plates in serious-to-critical condition Case study #2 Lower chord members & gusset plates in serious-to-critical condition Gusset plate with retrofit; up to 100% section loss in some plates. Buckled gusset plate between diagonal & vertical members

How Significant Issue Was Resolved Case study #2 First, strong-back system used to relieve stress on truss connections

Case study #2 Rivets replaced with bolts Old bearing pins replaced Lower chord members replaced. Rivets were removed.

Issue 2 – Repair historic concrete Case study #2 On concrete approach spans & abutments Delamination, spalling, graffiti Beams to be repaired Sidewalk brackets to be replaced

How Significant Issue Was Resolved Case study #2 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

How Significant Issue Was Resolved Case study #2 Sculpting architectural details Applying shotcrete to repair area

Replicating concrete sidewalk brackets Case study #2 After initial concrete demolition Building formwork Removing forms

Contractor demonstrating graffiti & paint removal Case study #2 Contractor demonstrating graffiti & paint removal Left: Using water – less effective Right: Using micro-abrasive blast – more effective Black Diamond product used

How was Section 106 handled Case study #2 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

How was Section 4(f) handled Case study #2 No 4(f) issues

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