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

Historic Covered Bridge Committee Notes of October 24, 2007 for:

WORRALL COVERED BRIDGE (#40) IN ROCKINGHAM

Present at Meeting:

• Committee members:
  • Mike Hedges
  • Warren Tripp
  • Eric Gilbertson
  • Nancy Boone
  • Bob McCullough
  • Pam Thurber
  • Scott Newman
  • Sue Scribner
• Also in attendance were:
  • John Weaver representing the Vermont Covered Bridge Society
  • Ron Joy of McFarland-Johnson, Inc.

Ron Joy provided a PowerPoint presentation to supplement a previously distributed Covered Bridge Summary Report. Following is a very brief summary – more detail can be found in the engineering report.

• General: Bridge is 15 – 16' wide and carries approximately 100 vehicles/day. The Williams River is prone to scour, aggradation and lateral migration. The approach span has a nail laminated deck – they keep adding gravel to build up. It is supported by I-beams and channels. The pier at the approach is encapsulated in concrete. It is recommended that the bridge be closed during construction and that the approach span be lengthened. Currently posted at H-8 load carrying capacity – not to change.
• Recommendations:
  • Remove and discontinue use of existing distribution beams
  • Realign the bridge – remove sweep and racking.
  • In-kind replacement of nail laminated deck
  • In-kind replacement of bolster beams
  • Complete replacement of primary lower chords with either select structural timbers or glu-lam
  • Partial replacement of secondary lower chords (retain ~ 45 – 50%)
  • Partial replacement of deteriorated full-height lattice planks (retain ~ 60%)
  • Partial replacement of upper chords (retain ~ 65 – 75%)
  • Replacement of both verticals at posts P1 and P6 and deteriorated interior posts
  • Addition of new endposts at the south end of the truss
  • Minimal replacement of existing floorbeams (retain ~ 95%)
  • Incorporate new bottom lateral bracing system
  • Replacement of siding and portal timbers as needed
  • Appropriate preservative and fire retardant systems
  • Replace north approach span and north abutment
  • Pending H&H analysis by Hydraulics Section, increase the length of the north approach span
  • Incorporate weathering steel approach guardrail
  • Enclose the existing SW masonry wingwall with stone fill
  • Incorporate new timber curbing
• General Discussion: Discussion on whether or not lattices should be sistered or replaced. Some existing short sisters are not doing much good. It was agreed that all recommendations would be followed with the following exceptions: The primary bottom chord will be replaced with glu-lam to reduce the amount of the secondary bottom chord that needs replacement - 25% replacement is the goal. "Bad" lattice tension members will be replaced but the areas of disassembly will be minimized. Lattice compression members will be repaired where possible, otherwise they will be replaced. Where possible in the secondary lower chord, cut out rot and butt splice laminations as this chord is not as critical. 4 lattice members near the ends of the bridge that do not rate will be replaced with stronger wood (5N, 6N, 18S and 19S). Ways to limit the amount of disassembly will be pursued. Finally, it was decided that the approach span length and profile will remain the same.