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

Historic Covered Bridge Committee Notes of February 14, 2002


Present at Meeting:

  • Committee members in attendance:
    • J. B. McCarthy
    • David Hoyne
    • Warren Tripp
    • Bob McCullough
    • Eric Gilbertson
    • Nancy Boone
    • Scott Newman
    • Sue Scribner
  • Also in attendance were:
    • Roger Whitcomb - Project Manager
    • Todd Sumner - Project Engineer
    • Joe Nelson representing the Vermont Covered Bridge Society
    • Michael Canavan from the Federal Highway Administration

This meeting was a follow-up to the last meeting held on November 26, 2001 where it was agreed that Scott Newman would further pursue whether it might be possible to consider installing glulam beams underneath the structure, considering approach grade and hydraulics.

Scott presented some Power-Point slides where 5-foot deep glulam beams installed underneath the structure had been superimposed. This demonstrated that, with the present approach grade, no impacts would be made below the Q100 level. It was questioned whether it might be preferable to install steel beams underneath as they would not need to be as deep and could be concealed by extending the siding. Discussion ensued relative to steel beams being more flexible than wood with different deflections resulting. The properties of glulam are much more compatible with wood than steel. The likely impact on the abutments was discussed. Both are laid-up stone and at one end in particular, a fair amount of stone would need to be removed to accommodate auxiliary support beams under the structure. It was agreed that the following three alternatives seem most reasonable for consideration:

  1. Remove the 8" high glulam beams currently in place, perform minimal but necessary repairs/replacement of members, and then use glulam beams underneath the structure as a supplemental system. Much of the structure has had changes, reinforcements, etc. made to date and much of this would remain.
  2. Remove the 8" high glulam beams currently in place and use glulam beams underneath the structure as a supplemental system but strive for an in-kind (same dimension, species and joinery) replacement of deteriorated members. It is recognized that a significant percentage of the members may require replacement but replicating the original engineering and craftsmanship is the objective.
  3. Replace most, and possibly all, of the existing members with new timber of larger size (and possibly species) to accommodate the desired loadings. No auxiliary support system would be used.

Discussion was suspended to discuss another covered bridge that was originally scheduled for this meeting. While available time was short, it was suggested at the end of the meeting that a vote be taken by those present on their preference of the above 3 options. All but 2 present voted for Option 2 above. It was agreed by those with the dissenting votes that direction could be provided to the Project Manager to move forward with Option 2. J. B. McCarthy, the Structures Program Manager, expressed possible concerns with the costs that might be associated with Option 2. We agreed that it would be left that the Committee recommendation will be to move forward with Option 2, but that if the Project Manager, during the course of project development, developed cost estimates that in his opinion render this option unreasonable, he will request another meeting of the Committee.

Respectfully submitted,
Susan Scribner

[This article was originally posted February 21, 2002]