salisbury cb pp

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Salisbury Station Covered Bridge: Location
  • Located 0.60 mi west of the village of Salisbury on the Salisbury Cornwall town line
  • Bridge 8 on T.H. 1/T.H.3 over the Otter Creek
  • Bridge is co-owned and maintained by the two Towns
  • Bridge currently posted for 3 tons

Salisbury Station Covered Bridge: Project History

Original Construction - 1865
  • ±154'-0" single span Plank (Town) Lattice Truss by unknown builders
  • Truss patented in 1820 by Ithiel Town, an architect from New Haven, CT
  • Web width of ± 5' -0" widest in Vermont
  • Constructed at a royalty of $1 /foot
  • Constructed to provide Cornwall with a link to railway shipping point in Salisbury
Major Rehabilitation 1969 (State Contract}
  • Pier added at mid-span to level up bottom chords and remove sag. Pier designed for H10 loading.
  • Abutments capped, re-pointed and/or faced and new treated shear beams placed
  • Other miscellaneous timber repairs
Major Rehabilitation - 1992 (J. Lewandoski)
  • Significant timber repairs, including replacing and/or "sistering" all broken or rotted chord and lattice members (Spruce timbers with hardwood pins)
  • Replacement of abutment bedding timbers (White Oak)
  • Other miscellaneous repairs
  • Repairs based on qualitative assessment
  • Cost: Approx. $50,000
Rehabilitation - 2005 (State Contract)
  • 1992 - State commissions consultant study for all VT covered bridges, to include recommendations for long-term preservation
  • 1995: McFarland-Johnson study completed for Station Bridge
  • Fall 1998: After preliminary meetings, State receives concurrence from both Towns to proceed as recommended in consultant study
  • Recommended option is to rehabilitate structure for moderate traffic
    • H10 (20,000 Ibs.) @ Inventory
    • H2O (40,000 Ibs.) @ Operating
  • Complete deck and floor replacement
  • Upgrade truss members where necessary
  • Other miscellaneous timber repairs
  • Miscellaneous substructure repairs
  • New approach rail and signing
  • Channel work
Priority of Treatments in CB Preservation Plan

Salisbury Station Covered Bridge: Examples of Current Problem Areas

Salisbury Station Covered Bridge: Roofing

New Roofinq - Summer 2002
  • Green standing seam metal roof
  • New purlin boards placed where required . Existing rafters retained
  • Cost: approx. $25,000
Analyze existing purlins and rafters for snow load. If structurally adequate, replace in-kind on a piece-by-piece condition assessment.
Other Roofing Considerations
  • Tie beams: Existing 6" x 8" timbers @ 10'-0" spacing
  • Lateral Bracing: Existing 6" x 6" timbers in 1 0'-0" bays
  • Knee Braces: Existing 2" x 6" timbers @ each tie beam
Analyze bracing system for wind load. If structurally adequate, replace in-kind on a piece-by-piece condition assessment.

Salisbury Station Covered Bridge: Proposed Truss Repairs

Existing Trusses
  • 3"x12" I.b.c, 2 }2"x11" u.b.c and I.t.c, 3"x11" u.t.c
  • 3"x11" lattices
  • Significant member replacement and/or sistering in 1992
  • All members Spruce-Pine-Fir No.1/No.2 (assumed)
Need further geometry and condition assessment for proper modeling
  • If feasible, all replacement members will be in-kind

Salisbury Station Covered Bridge: Truss Modeling Options and Issues

Option 1: Two-Span Continuous Trusses
  • 1A: Dead load and structural capacity from original timbers only
  • 1B: Dead load from 1992 timbers with no additional structural contribution
  • 1C: Dead load from 1992 timbers with additional structural contribution
Option 2: Two Simple Span Trusses
  • Same modeling options as above
Condition assessment critical
Live load objectives for rehabilitation
"1992" members historic?

Salisbury Station Covered Bridge: Proposed Floor Replacement

Existing Floor
  • 3"x12" runner planks over 2"x 6" diagonal flooring over
  • 3"x12" longitudinal deck planking
  • 4"x12" transverse floor beams @ varied spacing
  • 2"x 6" lateral bracing
Floor beams rate well below proposed loading
Proposed Floor
  • 6 3/4" longitudinal glulam deck panels over 1 0 1/2" x 15 1/8" transverse floorbeams spaced at 5'-3 5/16"
  • Floorbeams notched to retain existing vertical clearances
  • . Lag screws to stiffen floorbeams for live load deflection
  • Sacrificial wearing layer "built-in" to deck thickness
  • Curb placement to encourage centering of traffic and pedestrian safety
  • New lateral bracing
  • Southern Yellow Pine for new glulam members

Salisbury Station Covered Bridge: Project Typical Sections

Salisbury Station Covered Bridge: Miscellaneous Timber Repairs

Miscellaneous Timber Repairs
  • Replace damaged planking at portals
  • Replace damaged siding
  • Other miscellaneous timber repairs
  • Fireproofing?

Salisbury Station Covered Bridge: Fireproofing Options

  • Lighting: $6/SF
    • Place in upper rafters
    • Must be vandal resistant
  • Visible alarms
    • Portal areas
  • Fire detection systems: $7/SF
    • Linear heat detector wire threaded through bridge
    • Camouflage with proper coloring
  • Tele-metering
    • Used with linear heat detectors, system dials fire department if there is a fire
Reduce fire potential:
  • Intumescent paint: $6.50/SF
    • Raises flash point of timber
    • vailable in transparent finishes
    • Requires re-application every 5-10 years, especially on decks
    • Best suited, but not a 100% guarantee against fire
  • Fire retardant treated timbers
    • May reduce member strength 10-20%
    • Not logical unless treat entire bridge
Arresting the fire:
  • Hydrants
    • Recommended at both ends of bridge
    • Pressurized: $3500 ea.
      • Need connected water source
      • Usually not practical at CB locations
    • Dry: $2500 ea.
      • Uses water source on site
      • Maximum draw height approx. 30 ft.
  • Sprinkler System: $10.50/SF
    • Placed in roofing
    • Water drawn through dry hydrant
    • Open head system - no water in it because would freeze in winter
  • Depending on measures taken, may range from 3-15% of total project costs
  • Reduction in insurance premiums
  • Do nothing is an option!

Salisbury Station Covered Bridge: Proposed Substructure Repairs

Abutment No.1 (West Abutment - Cornwall Side):
  • Existing laid-up stone
  • Faced and top leveled in 1969 rehab.
Replace split or checked shear beams and blocking with new treated timber members
Architectural facing?
Abutment No.2 (East Abutment - Salisbury Side):
  • Existing laid-up stone
  • Wingwalls faced and top leveled in 1969 rehab.
  • Re-point/face remaining exposed masonry
Replace split or checked shear beams and blocking with new treated timber members
Architectural facing?
  • Existing bent-type pier: Concrete cap on single row of vertical steel piles constructed new in 1969
Analyze pier for proposed loading considering existing scour conditions
Replace split or checked shear beams and blocking with riew treated timber members

Salisbury Station Covered Bridge: Proposed Approach Improvements

Approach Rail:
  • Currently no rail on either approach
  • Qption 1: Steel backed timber rail
  • Qption 2: Heavy-duty steel beam weathering (or galvanized) rail on timber (or steel) posts with timber offset blocks
    • Both are crash tested, standard rail systems
    • Construct wingwall extensions for shoulder housing
    • Optional rail connection to bridge portal timbers
Other Approach Improvements
  • New pavement on both approaches
  • Narrow bridge and clearance signing
  • Other miscellaneous drive and grading improvements
  • Stone fill for bank stabilization

Salisbury Station Covered Bridge: Proposed Channel Work

Channel Work
  • Remove debris at upstream side of pier
  • Stone fill for bank stabilization

    Salisbury Station Covered Bridge: Plan and Elevation

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Joe Nelson, P.O Box 267, Jericho, VT 05465-0267

Text and photos by Vtrans Project Manager Roger Whitcomb, Project Engineer Mike Lozier, and team
This file posted March 19, 2004