thetford bridge notes

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Historic Covered Bridge Committee Notes of September 8, 2003 for:

Present at Meeting: Committee members J.B. McCarthy, Warren Tripp, Eric Gilbertson and Sue Scribner. Also in attendance were Mr. Mark McMahon from the Town of Thetford and John Weaver representing the Vermont Covered Bridge Society, VTrans project manager Alec Portalupi and project engineer Martha Evans-Mongeon

Martha Evans-Mongeon provided an overview of the bridge, its current condition and recommendations for the project scope through a PowerPoint presentation.

• General introduction to the bridge and its history. The bridge, known both as the Sayre Covered Bridge and the Thetford Center Covered Bridge, was built in 1839 and is of the Haupt design in combination with a through arch. It is 127 feet long and located on Tucker Hill Road (TH 29). In 1963, the then-existing timber deck and floor beams were removed and replaced with a nail laminated timber deck supported by four longitudinal steel beams. The original stone abutments were capped with concrete, the west abutment was faced with concrete and a concrete pier was constructed at the midspan of the bridge. A vehicle went through the north truss in 2002, damaging the truss system. The bridge is currently posted for 24,000 lbs. and sees significant amounts of car and truck traffic. It is a heavily used shortcut to both US 5 and I 91.
• Roof System - The existing corrugated metal roof is in good condition and it is proposed that it be saved. One of the portals was damaged in the 2002 collision and will need to be replaced.
• Truss System - It is proposed that the 2002 collision damage to the trusses be repaired, restoring the truss system as it was prior to being damaged. These repairs would be done with new members of the same size as the original. It is likely to affect 5 vertical members and 4 diagonal members. No other repairs or changes are anticipated. It was proposed that either curbing or a rub rail be installed to protect the trusses.
• Floor System - The current deck is in very poor condition. Ms. Evans-Mongeon proposed replacement of the existing deck with one of concrete. The town made it clear that this would not be received well. A glulam deck was then proposed, with enough depth to allow for some wear as this is a heavily used structure.
• Substructure – It is proposed that the voids in the stone portions of the abutments be re-chinked and that the abutments caps be replaced along with the bearings. Also, it is proposed that the bearings under the steel beams be replaced and the steel beams spot-cleaned and repainted.
• Siding – It is proposed that the existing siding be replaced in kind. There was discussion on using a fire retardant coating on the siding. There was also discussion on whether the structure originally had openings (windows) and if so, what size and how many. More information on this will try to be obtained. The town was asked if they wanted the end portals painted – they will get back to VTrans in this regard. Finally, there was speculation that the portal was probably different in appearance originally. More information on this will try to be obtained so that they can be restored to their original appearance.
• Discussion on Overheight Vehicles – The bridge has been hit repeatedly be overheight vehicles. In fact, it was hit the day the VTrans survey crew was on site a few weeks ago. The town has been concerned with this issue for some time and in fact, we have been working with them on a project to provide better advance warning to overheight vehicles. Ms. Evans-Mongeon has instead proposed that the trusses be raised. The truss was put up on "blocks" in 1963 and these could be replaced and raised to raise the trusses. The town thought perhaps raising them 6" would solve the problem but they will consider this further and let us know more definitively. We also discussed either installing stop signs or speed bumps to slow traffic prior to entering the bridge. The town will consider these options.

Per the Historic Covered Bridge Preservation Plan, the Priority of Use for the future disposition of this structure would be (B), Limited Use on Roads. Recommended work would result in Preservation Treatments 1 and 2 being employed.

Respectfully submitted,

Susan Scribner
Chair, Historic Covered Bridge Committee

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