V.A.O.T. Historic Bridge Committee
Historic Covered Bridge Committee Notes of February 11, 2004 for:|
CEDAR SWAMP (STATION) COVERED BRIDGE (#8)
IN SALISBURY AND CORNWALL
Present at Meeting: Committee members J.B. McCarthy, Warren Tripp, Scott
Newman, Eric Gilbertson, Nancy Boone and Sue Scribner. Also in attendance were Mr. Ed Peet,
the Cornwall Selectboard Chair, Mr. Don Shall from the Cornwall Historical Society, Mr. Joe
Nelson representing the Vermont Covered Bridge Society, VTrans Historic Preservation
Specialist Scott Gurley, VTrans project manager Roger Whitcomb, VTrans project engineer Mike
Lozier and project technician Gaston Roy.
Project manager Roger Whitcomb and project engineer Mike Lozier provided an overview of
the bridge and its current condition through a PowerPoint presentation.
- General introduction to the bridge and its history. The bridge was built in 1865,
spans 154 feet over the Otter Creek connecting the towns of Salisbury and Cornwall and is of the
town lattice design as patented by Ithiel Town in 1820. It has the widest lattice spacing known of
any town lattice covered bridges in Vermont at 5-foot spacing. It was constructed at a royalty of
$1/foot to provide Cornwall with a link to railway shipping in Salisbury. The bridge is currently
posted for 3 ton with a 15-mile detour. The results of the McFarland-Johnson, Inc. report done
for the bridge in 1995 has previously been shared with the towns; the report states that it is likely
that the trusses could support an H20 loading if rehabilitated but it is presently limited by the floor
system. In 1998 the Agency received concurrence from both towns to move forward with
rehabilitation as recommended in the McFarland-Johnson, Inc. study. The Town of Cornwall
through their representative at the meeting emphasized that it would like to see the carrying
capacity increased to H20 loading. The Otter Creek floods at the bridge and the approach roads
are closed for some periods of time each year.
Various repairs have been made to the structure over the years. The Agency oversaw a
project in 1969 that involved various timber repairs and the addition of a pier at mid-span
designed for H10 loading to level up the bottom chords and remove sag. In addition, the
abutments were capped, re-pointed and/ or faced and new treated shear beams were placed. In
1992, the towns hired Jan Lewandoski to rehabilitate the structure. Mr. Lewandoski's work
included significant timber repairs such as replacing or sistering all broken/ rotted chord and
lattice members with spruce. Abutment bedding timbers were replaced with white oak and other
miscellaneous repairs were done. Finally, a new standing seam roof was added to the bridge
during the summer of 2002 through an Agency project with some roof sheathing replaced.
- Roof System - It is the intent to salvage the new roof if possible. The bracing
system will be analyzed for wind load and the existing rafters for snow load. If structurally
adequate, members will be assessed individually for wear and replaced as needed with in-kind
- Truss System - Further condition assessment is needed. Some tails of the lattices do
not appear to extend adequately below the bottom chord and some of the treenails are in poor
shape. It appears that a significant amount of the bottom chords were replaced in 1992 as well as
approximately one-third of the top chords. It is proposed that all members needing replacement
be replaced in-kind. However, the designers are still struggling with the modeling and structural
analysis for this structure and it is not yet known if this will be feasible.
- Floor System - The existing floor system consists of 3"x12" runner planks over
2"x6" diagonal flooring over 3"x12" longitudinal deck planking. The 4"x12" floor beams are at
an unusual and varied spacing and there is 2'x6" lateral bracing. It was proposed that glulam deck
panels be installed over 10 1/2"x15 1/8" floorbeams at regular 5'-3 5/16" spacing. Eric Gilbertson
stated that he would like to see if the present, irregular floorbeam spacing will work if glulam
members are used, even if member sizes need to be increased. It was proposed that running
boards not be replaced but curbing was suggested inside the structure to both protect the
structure and offer some refuge to pedestrians. New lateral bracing is proposed as well.
- Substructure --The abutments are in pretty good shape and no major work is
anticipated. Split or checked shear beams and blocking would be replaced. The pier will need to
be analyzed for proposed loading considering existing scour condition. It was proposed that
debris be removed at the upstream side of the pier.
- Approaches -- It was proposed that either weathering-steel w-beam or steel-backed
timber guardrail be used on the approaches. New pavement on both approaches was proposed as
well as appropriate signing and miscellaneous drive and grading improvements. As well, stone fill
for bank stabilization was proposed.
- Siding -- The siding is routinely damaged at the bottom by floating debris and ice and
has been replaced many times. It is proposed that damaged members be replaced in-kind. The
siding is not presently continuous in its height; this was discussed along with the probability that
members the height of the bridge might not have been available at the time the bridge was built.
- Miscellaneous -- The Town of Cornwall is concerned about fire. Various detection
and retardant measures were discussed at the meeting and will need more input from the towns.
Warren Tripp relayed that we are pursuing a research project on the bridge to measure deflections
which will hopefully help develop new distribution factors. Nancy Boone asked if we could wait
until the research has been completed before moving forward with design details but, as this is not
expected to be completed until sometime this summer, the timing will not work.
It appears that quite a bit of further analysis is required and another meeting is anticipated.
The project engineers were looking for input on direction of the project early on and their efforts
to date were acknowledged and very much appreciated.
Chair, Historic Covered Bridge Committee