Quinlan Covered Bridge

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					                       Quinlan Covered Bridge
             Monkton Rd. (TH-36) over Lewis Creek, Charlotte VT
                             October 25, 2010

   Presented by
    VTrans - Mark Sargent                Presented to
    VHB - Mark Colgan                     Town of Charlotte
    Vanasse Hangen Brustlin, Inc.
Quinlan Covered Bridge




Project Overview
                   Quinlan Covered Bridge
                    • National Register of Historic Places – 1974
                    • One of three covered bridges In Charlotte
                    • One of nine Burr Arch bridges in Vermont


                   Single-span Kingpost Truss with Burr Arch
                      g
                    Single lane - 12’-11” clear width
                   87’ deck length, 11’-5” vertical clearance
Quinlan Covered Bridge




    g
Bridge Location
Quinlan Covered Bridge




    Project Goals
             Supe st uctu e e ab tat o
              Superstructure rehabilitation
             Repair deteriorated timber trusses
             Keep bridge in use for community vehicles
             Extend life of 160 year old bridge
Quinlan Covered Bridge




                         History
                            Built 1849
                            Historic Photos
                             • End portal modifications
                             • Shelter panels removed
Quinlan Covered Bridge




History
          12-11” clear width
          11’-5” vertical clearance

          1985 Rehabilitation
           • Replaced deck & floorbeams
           • Added steel girders

          Other Changes
           • Relocation of knee braces
           • Selected member replacement
Quinlan Covered Bridge




Current Conditions




                         Roofing and Siding
Quinlan Covered Bridge




Current Conditions




                         Framing Members
Quinlan Covered Bridge




Current Conditions




         2x10
         2 10            Timber/Steel    Delaminated
    Wearing Surface      Floor Framing   Steel Beams
Quinlan Covered Bridge




Current Conditions




                         Impact Damage - Arches
Quinlan Covered Bridge




Current Conditions



                           Truss
                         Top Chords
Quinlan Covered Bridge




Current Conditions




                         Trusses – Top Chords at Roof Framing
Quinlan Covered Bridge




Current Conditions




                         North Abutment & Wi
                         N th Ab t            ll Erosion
                                      t Wingwall – E i
Quinlan Covered Bridge




Current Conditions




                                pp
                         South Approach
Quinlan Covered Bridge




Current Conditions




                         North Approach
Quinlan Covered Bridge




Vehicle Loading for Structural Analysis




                         H17         H17




                         H25        H24
Quinlan Covered Bridge




Vehicle Loading
                  Vehicle                           Equivalent Loading
                  Town Plow Truck (with sand)       H25
                  Fire Engine                       H24
                  School Buses
                  School Buses                      H17
                  Fuel Oil Truck (full)             H17
                  Town Tandem Dump Trucks (empty)   H12
                  Current Posting ‐ Car Traffic     H5
Quinlan Covered Bridge




Bridge Rehabilitation - Structural Analysis
                                    g     g       g
              Alternative 1 - Existing Bridge Configuration
              • Load sharing between steel girders and timber arch/trusses


             Alt    ti       Original Configuration
              Alternative 2 - O i i l C fi      ti
              • Remove steel girders


             Alternative 3 - Isolate Trusses from Floor Framing
              • Steel girders carry deck dead load & vehicle live load
              • Timber trusses carry truss self-weight & roof loads
Quinlan Covered Bridge




Bridge Components




        p
    • Top/Bottom chords   • Diagonals
    • Arch                • Floorbeams
    • Vertical Posts      • Arch bearings
Quinlan Covered Bridge




Alternative 1 – Existing Configuration
       Steel girders added in 1985 to
        support school buses
       Girders were designed for H15
                  p
        live load plus 100% dead load
       “Backup” system in case of truss
        failure
Quinlan Covered Bridge




Alternative 1 – Existing Configuration
       Analysis Results:
        •   Unrealistic to upgrade for H25 plow truck load
        •   H17 load rating for school bus reasonable
        •   Floorbeam capacity limited and needs upgrading (H10 now)
        •   Steel girder rating H22

                                                                bus),
    Conclusion: Design H17 inventory rating (frequent school bus)
    and H25 operating rating (infrequent fire truck). No plow truck.
Quinlan Covered Bridge




Alternative 1 – Existing Configuration

                   Upgrading needed f H17 rating:
                    U    di      d d for     ti
                    •    Replace top chord with larger/stronger member
                    •     pg                 g
                         Upgrade arch bearing details
                    •    Reinforce end diagonals
                    •    Add sister floorbeams
                    •    Reinforce bottom chord
                    •    Upgrade connections throughout
Quinlan Covered Bridge




Alternative 2 – Original Configuration
            Arch provides 30%-40% of strength
            Deck load capacity rating:          H25
            Floorbeam load capacity rating:     H5
            Trusses chords:                     H5


         Conclusion: Design for passenger vehicles only (H5)
Quinlan Covered Bridge




Alternative 2 – Original Configuration
                   Upgrading needed for H5 rating:
                    •    Replace top chord with larger member
                    •    Upgrade arch bearing details
                    •                     g
                         Reinforce end diagonals
                    •    Upgrade bracing & connections
                    •    Bottom chord has little capacity for overload
                          o   Strict load enforcement required
Quinlan Covered Bridge




Alternative 3 – Truss Isolated from Floor
     Minimize load on truss = minimize upgrade req’d
        “Sever” connection b t
      • “S     ”        ti between fl b                t
                                       floorbeams & trusses
      • Steel girders support all floor loads (inc. live load)
      • Trusses support only truss self-weight & roof load
Quinlan Covered Bridge




Alternative 3 – Truss Isolated from Floor
                   Floorbeam Rating:
                    • H17 at inventory (= school bus)
                    • No good for H25 plow truck
                               p     g (close enough to H25 fire truck)
                    • H23 at operating (           g                  )
                   Girder Rating:
                    • H22 at inventory (ok for school bus)
                    • >H25 at operating (ok for fire truck)

                   Conclusion: Design for H17 inventory (school bus)
                                ti (fire truck),   l   truck
                    & H25 operating (fi t k) no plow t k
Quinlan Covered Bridge




Summary of Alternatives
                           Alternative 1               Alternative 2               Alternative 3
                           Existing Configuration      Original Configuration      Isolate Trusses

              Inventory    H17                         H5                          H17
              Live Load    School bus                  Passenger car               School bus

              Operating    H25                         No vehicles larger than     H25
              Li L d
              Live Load    Fire truck
                           Fi t k                      passenger cars              Fire truck
                                                                                   Fi t k

              Req’d        ‐ Upgrade bracing &         ‐ Upgrade bracing &         ‐ Upgrade bracing & 
              Structural     connections                 connections                 connections
              Upgrades     ‐ Larger top chord          ‐ Larger top chord
                           ‐ Upgrade arch bearings     ‐ Upgrade arch bearings
                           ‐ Reinforce end diagonals   ‐ Reinforce end diagonals
                           ‐ Sister floor beams        ‐ Add tension diagonals 
                                                         near midspan
                                                       ‐ Improve bottom chord
                                                         Improve bottom chord
Quinlan Covered Bridge




Rehabilitation
       Most of the required timber rehabilitation work is to
        address deterioration which is required for all three
        alternatives.

       Some additional work is needed for structural
        upgrades; scope varies depending on the selected
        alternative.
        alternative
Quinlan Covered Bridge




Selection of Rehabilitation Alternative
       Vermont Historic Covered Bridge Guidelines
        • Priority of Use – achieve maximum users
        • Priority of Treatments – maintain character of materials
                           g     p            g         g
        • Maintain working components of original bridge timbers
Quinlan Covered Bridge




Alternative 1 – Existing Configuration
       Consistency with Historic Covered Bridge Plan:
        • Bridge remains in service for up to H20 loading (40,000 lbs)
        • Alternate route exists for heavier vehicles
                 g
        • Existing timber members remain in functional use



                                                             use.
             This Priority of Use maintains existing vehicle use
Quinlan Covered Bridge




Alternative 2 – Original Configuration
       Consistency with Historic Covered Bridge Plan:
        •   Bridge remains in service for light traffic (passenger cars)
        •   Relatively short alternate route exists or can be constructed
        •                g        g
            Restore bridge to original condition
        •   Existing timber members remain in functional use



    This Priority of Use does not maintain existing use.
Quinlan Covered Bridge




Alternative 3 – Isolate Trusses
       Consistency with Historic Covered Bridge Plan:
        • Bridge remains in service for up to H20 loading (40,000 lbs)
        • Alternate route exists for heavier vehicles
                                      g       y g                  g
        • Truss members are no longer carrying live load thus bridge
          effectively becomes a “steel beam bridge”



    This Priority of Use maintains existing vehicle use but
    does not maintain use of original timber bridge
    components.
    components
Quinlan Covered Bridge




Rehabilitation
       September 2010 Covered Bridge Committee
        Unanimously Recommended Alternative 1 - Existing
        Condition


       Priority of Use is the closest fit
        •   Satisfies intent of Historic Covered Bridge Plan
        •   Maximizes preservation of historic fabric
        •   Original components remain functional parts of the structure
        •                              co-functional            system”
            Steel girder in spirit of “co-functional reversible system
Quinlan Covered Bridge




Rehabilitation – Alt 1 (Existing Configuration)
                                   •   Replace Top chord
                                       with larger member
                                   •   Sister floorbeams at
                                       posts with 6x12’s
                                   •   Notch intermediate
                                       floorbeams
                                   •   Paint steel girders
Quinlan Covered Bridge




                       (       g      g       )
Rehabilitation – Alt 1 (Existing Configuration)




               •   Top chord replacement   •   Reinforce end diagonals
               •   Sister floorbeams at    •    pg                g
                                               Upgrade arch bearings
                   posts                   •   Replace connections
Quinlan Covered Bridge




                       (       g      g       )
Rehabilitation – Alt 1 (Existing Configuration)




               •   Sister floorbeams at   •   Notch intermediate
                   posts                      floorbeams
Quinlan Covered Bridge




Rehabilitation
       Deck - Add curbs to keep vehicles centered
       Steel Girders - Clean & paint, replace bearings
       End Portal
        • Reconstruct portal similar to original
        • Express knee braces at exterior to warn drivers
        • Maintain existing clear height
Quinlan Covered Bridge




Rehabilitation
       Abutments & Wingwalls
        • Patch deteriorated concrete surfaces
        • Patch sink hole, remove debris


       Approaches
        • Add wingwalls/reinforce slopes to prevent erosion at roadway
        • Re-grade stone file & remove existing trees
        • Add end posts to guardrails so not connected to bridge
Quinlan Covered Bridge




Rehabilitation
       Fire Protection & Detection Options
        • Treat all exposed surfaces with fire retardant to slow spread of fire
        • Install heat detecting cable with alarm to alert fire department
          Dry   i kl      t  (deluge t
        • D sprinkler system (d l        ) ith t d i for          ti
                                     type) with standpipe f connection
          to pumper truck
Quinlan Covered Bridge




Schedule
       Begin Final Design Engineering 2010
       Environmental Permitting underway
       Complete engineering and permitting end 2011
       Construction 2012 or 2013
Quinlan Covered Bridge




Questions/Comments?

				
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posted:10/11/2011
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