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Cedar Swamp Covered Bridge Renovation Update [VT-01-01]*
by Jim Ligon
Cornwall, Vt, December 19, 2007 - Hi Joe--A brief update on what we're up to:
The 1865 Town lattice bridge has been lifted over 6 feet and a temporary steel bridge was built underneath to support it. A 2nd temporary structure was built on top of that so we could actually hang the stripped timber bridge by the unloaded upper members.
Initial contract estimates of timber replacement was way off because it's impossible to see the extent of damage until the structure has been supported and can be disassembled.
The full length of lower bottom chord both sides need replacement, as do many of the lattice members. The major factors are very poor initial design and construction, and subsequent overloading.
Many of the original lattice members were notched vertically between trunnel holes. I have no idea why they did that, but it allowed each point to slip. With literally thousands of points, it slipped a lot. It slipped until it broke. Then they added a pier in the middle of the river.
A pier, of course, has its own issues. They trap silt, which traps logs, which traps every other thing coming down the river. And when they all come together they hit the bridge right in the middle...Our contract called for us to clear the accumulated debris but not touch the bottom. We cleared the debris first thing, now it's back, just as it is every year.
Oh, and many many of the original trunnel holes were drilled right at the edge of a member. Many actually split members. Bad design! For historical sake we're supposed to duplicate those structural errors? Not a good idea. Now we have saved timbers with holes drilled right out the edge or bottom which do nothing but weaken the member.
We're halfway finished replacing lattice members. Bottom chord members follow as we get to themn. Progress is good and weather is as usual in a Vermont winter. We're bundled up and working.
[Jim Ligon is construction supervisor for contractor Alpine Construction, of Stillwater, N.Y.]
* Also known as Swamp Road Bridge or Salisbury Station Bridge. The span is jointly owned by the towns of Cornwall and Salisbury.
For a history of the bridge and an engineering assesment with photos, go to
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Joe Nelson, P.O Box 267, Jericho, VT 05465-0267
This file posted 12/22/2007