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A refined Analysis of the Bartonsville Covered Bridge
Town Lattice Truss Completed.

By Philiip C. Pierce, P.E.

October 7, 2000 - I sent out my final report on the refined analysis of the Bartonsville Covered Bridge last week and I have talked to the owner of the bridge and my client: the Town of Rockingham. I also sent a copy of the report to the VAOT and have talked to them.
       The Town Lattice trusses at Bartonsville were found to have suspect strength as a result of the Statewide Study, yet that work was based on a very cursory analysis. The Study could not fund a thorough analysis of all 75 bridges - hence the more simplified approach. The bridge has been posted at 3 tons since the Study (See Editors note below).
       I have concluded, after exhaustive work, that I am willing to increase the capacity to 17 tons for permit vehicles. According to state practice, the bridge would still be limited to a posting of 16,000 pounds as a consequence of having a timber floor. In my opinion, this is good news for Rockingham, and they agree.
       My work has included the preparation of a three dimensional, finite element computer model and has included field testing to verify the results of the computer simulation.
       While being similar to work done at the Brown, Paper Mill, and Hopkins covered bridges, the analysis work has continued to evolve further into the realm of unknowns with the bottom chord/lattice connections (in my opinion, these connections are the key to the analysis of a Town Lattice truss).
       I believe this work has pushed the envelope and is getting closer to quantifying the "hidden reserve" of these bridges. More could be done, but I ran out of time and money in this assignment. More efforts will hopefully follow on another bridge.
       While I am in no way able (or motivated) to speak for the VAOT about the ramifications of this work, I believe that the several other Town Lattice bridges, found to have similar suspect capacity as a result of the Study, may benefit from such an investigation. It is not cheap and takes a lot of work, but raising the capacity without doing any field work is attractive.
       I hope to discuss the results of my work with VAOT shortly. It may generate interest in tackling some of the other bridges in a similar situation.

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Mr. Pierce owns and operates Phillip C. Pierce, P. E., a consulting engineering practice specializing in covered bridges. Mr. Pierce has over 27 years of experience with diverse bridge and highway engineering assignments while employed within other consulting engineer firms.

Editors note - The Statewide Study referenced above alludes to the Long-Range Planning Study of Town-Owned Covered Bridges. This Study was sponsored by the Vermont Agency of Transportation and completed by a consulting engineering team led by McFarland-Johnson, Inc., of Binghamton, New York. Mr. Pierce served as the Project Manager for the Study. The focus of the Study was to develop a long-range plan for preservation of all of the bridges for the indefinite future.
        The Study included an exhaustive evaluation of all aspects of the bridge, including current and future traffic needs, as well as an evaluation of the structural condition and needs of the bridge. Five preservation plans were investigated at each bridge -- from keeping the bridge open to moderate traffic to rehabilitation of the bridge or constructing a bypass structure if the covered bridge was found to be unable to economically and/or safely support the traffic needs. No covered bridges were to be destroyed -- all to be preserved whether able to remain open to traffic or not.
        The Study was completed in 1995 and included seventy-five covered bridges and culminated in a report for each bridge which was provided to its Town owner to help them decide which preservation action to pursue for the bridge.
        During the course of the survey, some of the bridges were found to be theoretically unsafe, in which case traffic weight restrictions were recommended until such time as more extensive engineering evaluation was possible. The Bartonsville Covered Bridge was one such structure. Hence, the work reported on herein, was sponsored by the Town of Rockingham as a result of the early finding of suspect strength. Mr. Pierce conducted the work under contract to the Town.

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Joe Nelson, P.O Box 267, Jericho, VT 05465-0267
This file posted March 13, 2001, revised April 26, 2006