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V.A.O.T. Historic Bridge Committee Proceedings

Historic Covered Bridge Committee Notes of March 2, 2006


Present at Meeting:

  • Committee members:
    • Warren Tripp
    • Nancy Boone
    • Sue Scribner
  • Also in attendance were:
    • Joe Nelson representing the Vermont Covered Bridge Society
    • John Weaver - VTrans project manager
    • Consulting team:
      • Steve Hodgdon of VHB
      • Phil Pierce - sub consultant
      • Michael Weitzner - master stone mason
    • Structures Section:
      • Mark Sargent
      • Chris Williams
      • Rob Young

Steve Hodgdon of VHB gave a PowerPoint Presentation outlining the existing conditions at the bridge site along with some of its history. This provided information in addition to that provided in a Structure Rehabilitation and Alternatives Assessment Report of February 6, 2006 that had previously been distributed to committee members.

The consultant team did a good job presenting their material in relationship to the Historic Covered Bridge Preservation Plan and its Priority of Treatments and Priority of Uses. Superstructure recommendations are as shown below. The consultant recommends that steel beams remain under the bridge if emergency vehicles are to use the structure; the bridge provides the only access to several homes so this is necessary. A summary of the recommendations for the superstructure is as follows:

  • Repairs and or replacement of individual members as indicated in the diagrams below. All replacements to be of same dimension as original
  • Retention of all metal rods
  • Replace siding in-kind
  • Apply fire retardant
  • Retain collar ties
  • Paint knee braces to enhance visibility
  • Replace floor system with new galvanized, painted steel beams of slightly shallower depth to increase hydraulic capacity with nail laminated wood deck
  • Install timber curb along edge of deck and raise trusses by approximately one foot to provide additional vehicular clearance to minimize impact damage
  • Approach rail at all four corners

The presentation also included discussion on the substructure. The abutments are in very poor shape; the abutment at the west end is in critical condition with many voids. There is consensus that the existing abutments cannot be saved. Therefore the discussion moved on to whether the existing abutments will be replaced with new laid-up stone abutments or with concrete.

Mr. Weitzner was present as a professional member of the Dry-Stone Walling Association of Great Britain and has extensive experience with laid-up stone structures. Mr. Weitzner reported that he would be cautious about using the same type of stone as is there presently (schist). He would want to ensure that settlement will be uniform, i.e. spread out evenly. He recommends using larger stone at the bottom courses as they would be a lot stronger. Pros and cons on masonry abutments were detailed as follows:

  • Stone has long term durability
  • Stone would be in keeping with historic fabric
  • Stone would be more aesthetically pleasing
  • Stone abutments would cost approximately $50,000 - $60,000 more than concrete
  • Stone abutments would require use of a skilled mason to ensure work is constructed properly
  • A consistent stone source might be difficult to find for the size of stone needed

For concrete abutments, pros and cons are as follows:

  • Typical construction for bridge contractors
  • Can be constructed with vertical face to increase hydraulic capacity
  • Smaller footprint at a site with tight constraints
  • More formwork and "in the dry" construction required as well as curing time for each concrete pour
  • Aesthetically not as pleasing

A lot of discussion followed on the specific site conditions that exist.

A motion was made as follows: The committee accepts the recommendations for the concept and scope of the covered bridge rehabilitation and recommends that the replacement of substructure with either stone or concrete be left to later. Further, it was recommended that the project manager pursue a phased project, i.e. that a temporary bridge be installed as soon as possible and the trusses removed. The one exception to the consultant’s recommendations is that the committee would not like to see the knee braces painted.

The motion was seconded and passed.

Respectfully submitted,

Susan Scribner

[This article was originally posted May 12, 2006]

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