V.A.O.T. Historic Bridge Committee Proceedings
Poland Covered Bridge Meeting with Historic Bridge Committee
- VAOT has produced a set of plans showing existing details. Preliminary plans indicating rehabilitation
work shall be finished soon. Final plans for the rehabilitation project are scheduled for end of September
01. Another Committee meeting regarding this bridge will take place in Sept. 01.
- D. Hoyne outlined the scope of rehabilitation work:
- 3 ton live load capacity per town requirements.
- Restore shape to bridge -- 12" positive residual camber. 18" sag at present.
- Move bridge to staging area -- not disassemble.
- Overcome fit up problems to produce proper positive camber.
- Warren Tripp stated three options:
- Shoring in place
- internal supports in place
- moving the bridge to a staging area for rehabilitation and repairs
- Warren also stated that the choice of option should be left up to the contractor,
not determined in advance.
- Question from DHP: Will arch restoration provide relief to overstress at end diagonals (braces)? D. Hoyne
responded yes, if the shape (camber) of the bridge is restored, the existing end diagonals will remain in place
and be ok for stress.
A further question was raised about the function of the arches: Are these really tied arches (tied to superstructure)
or do the arches develop compression against the thrust blocks?
- It was mentioned that at the last meeting in April VAOT would develop rehabilitation options for presentation:
D. Hoyne stated that sawn plank floor and glulam floor systems were considered. VAOT recommendation is to eliminate
newer existing floor beams, spanning 8" - 9" between existing historic floor beams with a glulam deck. J. Weaver
stated that the existing 8 x 12 historic floor beams would not handle that span for 3 ton live load and glulam dead
load. Moments would be excessive.
- Member replacement:
- D. Hoyne stated the following:
- Bottom chord channel, rods and existing wood chords to remain in place.
- A few diagonals to replace, a half dozen kingposts to replace.
- At bottom splice bolted connections, restore rod holes with bushing trunnel liners.
- Warren Tripp stated that it would be best to shim gaps between existing members (diagonals, etc.)
caused by re-cambering, etc., to cut down on member replacements.
- Eric Gilbertson suggested profiling the channnel/rod system downward (if possible) to help
maintain positive camber.
- J. Weaver pointed out that there are three systems of tension transfer at the bottom chords: The
timber notches at kingposts to chord, the scarfed joints and the rod/channel system.
- The Structures Section has not yet undertaken materials evaluation or species ID of existing bridge members.
Species ID through HTA was suggested by D. Hoyne.
- Substructure work: Concrete bathtub sections were suggested at approaches to the bridge. Mike Fowler said that
Joe Nelson had suggested stone work buildups at a VCBS meeting last Saturday. D. Hoyne suggested laid up stone with geotextile
reinforcement (tiebacks) for the wings, concrete caps for the new bridge seats.
- Vertical profile of bridge: Will use elevations from flood insurance maps, hopefully maintain present vertical profile elevations.
[This article was originally posted February 13, 2002]