ST' LOUIS MERCHANTS BRIDGE DECK TRUSS REPLACEMENT

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ST. LOUIS MERCHANTS BRIDGEDECK TRUSS REPLACEMENT
ASCE 2006 Structures Congress May 18-20, 2006 St.
Louis, Missouri Mark Lasseigne, P.E., S.E. and
Aaron Kober, P.E. Modjeski and Masters, Inc.
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HISTORY BACKGROUND

• Located North of Downtown St. Louis
• Designed by George Morison and E. L. Corthell
• Built by Union Bridge Company of New York
• Completed in 1890
• Owned and Operated by the Terminal Railroad
  Association of St. Louis
• Services 35 Trains Daily for Local and
  Transcontinental Railroad Traffic

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ORIGINAL CONSTRUCTION
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ORIGINAL CONSTRUCTION
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EXISTING STRUCTURE

• Main Truss Spans Three 518-foot Pennsylvania
  Trusses, supported atop granite and limestone
  piers
• Deck Truss Spans Three 125-foot spans at each
  approach, supported atop steel towers with timber
  pile-supported cylinder piers
• Deck Girder Approach Spans Built-up deck girder
  spans, supported atop steel towers with timber
  pile-supported concrete pedestals

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STRUCTURAL EVALUATION (1999)

• Evaluation
• Comprehensive Inspection
• Structural Rating
• Fatigue Study
• Seismic Evaluation
• Recommendations
• Increase Frequency of Deck Truss Inspections
• Near-Immediate Replacement of Deck Truss Spans

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STRUCTURAL EVALUATION (1999)

• Evaluation
• Comprehensive Inspection
• Structural Rating
• Fatigue Study
• Seismic Evaluation
• Recommendations
• Increase Frequency of Deck Truss Inspections
• Near-Immediate Replacement of Deck Truss Spans

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INSPECTION FINDINGS

• Deterioration
• Pin Wear
• Member Fracture

• Cracking
• Crushed Bearings
• Truss Movement

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INSPECTION FINDINGS

• Fracture

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INSPECTION FINDINGS

• Cracks

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INSPECTION FINDINGS

• Pin Wear

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INSPECTION FINDINGS

• Bearing Locations

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INSPECTION FINDINGS

• Deterioration

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INSPECTION FINDINGS

• Crushing

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INSPECTION FINDINGS

• Movement

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STRUCTURAL EVALUATION (1999)

• Evaluation
• Comprehensive Inspection
• Structural Rating
• Fatigue Study
• Seismic Evaluation
• Recommendations
• Increase Frequency of Inspections
• Near-Immediate Replacement of Deck Truss Spans

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DECK TRUSS CONCERNS

• Structural Reliability
• Loads vs. Capacity
• Design capacity is E40
• Current traffic is comparable to E72 live load
• Main members are typically adequate to carry E72
  loads
• Current design standard is E80
• Condition and Stability
• Truss distortion, pin wear and section loss are a
  concern
• Many column caps have crushed or otherwise failed
• Pumping and deterioration is significant

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DECK TRUSS CONCERNS

• Remaining Serviceable Life
• Fatigue Life
• Potential for cracking in fatigue-prone members
  is increased
• Floor system has exhausted its remaining safe
  life
• Main diagonals are approaching the end of their
  safe life
• Economic Life
• Spans inspected for problems every six months
• Significant number of repairs have already
  occurred
• Some repairs are temporary fixes
• Internal, operational and intangible cost of
  maintaining the spans is significant

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DESIGN RESTRICTIONS

• Rail Traffic Restrictions
• Minimal disruption to traffic required
• Two ten-day track outages allowed for
  demolition/construction (staged replacement)
• One track must remain in service at all times
• Much of the structure will have to be built with
  the existing spans in place
• Existing structure limits overhead clearance

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DESIGN RESTRICTIONS

• Obstruction and Utility Restrictions
• Abandoned underground brick sewer
• 108 working underground sewer
• High voltage overhead power lines
• Underground water, fiber-optic, gas and electric
• Underlying BNSF tracks
• Flood Wall
• Bike Trail
• On-Structure Utilities

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DESIGN CONSIDERATIONS

• Live Load
• Existing structure was designed for Cooper E40
• New structure to be designed for Cooper E80
• AREMA Longitudinal Force (2003)
• Load is significantly increased from previous
  guideline
• Forces must be applied simultaneously to both
  tracks
• Geometric restrictions create design limitations
  (fit)
• Adjustment to longitudinal forces was required

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DESIGN CONSIDERATIONS

• Fit (West Approach, Before Bent Construction)

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DESIGN CONSIDERATIONS

• Fit (West Approach, After Bent Construction)

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FOUNDATION DESIGN ADJUSTMENTS

• Original Design
• 36 diameter drilled shafts
• Founded at bedrock
• 36 rock socket
• Complications
• Low overhead clearance
• Lengthy installation process
• River level complications
• Flow of liquefied material into shaft excavations
• Loosened sand causing existing foundation
  settlement

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FOUNDATION DESIGN ADJUSTMENTS

• Steel Micropile Alternative
• Adequate capacity
• Cost-effective
• Quick installation
• Adaptable to low overhead clearance

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FOUNDATION DESIGN ADJUSTMENTS

• Modified Foundations
• Drilled Shafts
• Use at Bents E1 and W1 (river locations)
• Utilize increased overhead clearance
• Guard against scour
• Micropile
• Use at remaining locations
• Increase number of piles per foundation
• Batter piles to handle longitudinal forces
• Increase length of rock sockets to five feet
• Perform load tests to twice the design load

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CONSTRUCTION SEQUENCE

• Center Truss Key to Staged Construction

Section at Mid-Span
Section at Tower
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CONSTRUCTION SEQUENCE

• STEP 1 - Foundations

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CONSTRUCTION SEQUENCE

• STEP 2 - Footings

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CONSTRUCTION SEQUENCE

• STEP 3 Bent Walls

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CONSTRUCTION SEQUENCE

• STEP 4 Shaft Extensions

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CONSTRUCTION SEQUENCE

• STEP 5 Bent Caps

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CONSTRUCTION SEQUENCE

• STEP 6 North Truss Removal

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CONSTRUCTION SEQUENCE

• STEP 7 Deck Girder Spans

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CONSTRUCTION SEQUENCE

• STEP 8 Remaining Truss Removal

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CONSTRUCTION SEQUENCE

• STEP 9 Deck Girder Spans

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CONSTRUCTION SEQUENCE

• COMPLETED STRUCTURE

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QUESTIONS?