December 1, 2010
Town Highway 36 over Lewis Creek, Charlotte
Attendance: VTRANS: J.B. McCarthy, Mike Hedges, Wayne Symonds, Scott Newman, Kaitlin O'Shea, Mark Sargent (project manager), Pam Thurber, and Bob McCullough (Historic Bridge Program); Vermont Division for Historic Preservation: Nancy Boone; Vanasse Hangen Brustlin, Inc., Consulting Engineers: Mark Colgan; Preservation Trust of Vermont: Eric Gilbertson; John Weaver (Vermont Covered Bridge Society); Town of Charlotte: Dean Block, Charles Russell, Marty Imick, and Hugh Lewis, Jr.
Introductory Presentation: J.B. McCarthy and Mark Colgan apologized for the oversight in not notifying town officials about the previous meeting in September and then discussed the town's concern about the need for its loaded highway maintenance truck, H25 loading, to use the bridge. The proposed alternative achieves only an H17 loading, adequate for school buses but not the maintenance vehicle. Town officials had inquired whether it would be possible to increase the secondary steel support system in order to achieve the H25 load. Subsequent discussion focused on the exact weight of the maintenance vehicle - loaded or partially loaded, and calculated the figure roughly to be between H23 and H25.
Mark Colgan explained that the engineering problem is not inadequate strength of the steel structural system but rather that the steel girders are more flexible than the combined timber truss-arch system and deflect to a greater extent when carrying loads, as much as an inch or more. Because the floor system of the Burr arch-truss is tied to the steel girders, the former flexes as much as the steel girders, creating excess stress on the joints of the arch-truss system. Eventually, that stress will cause the arch-truss system to fail. By limiting the loading to H17, the timber structure would be capable of carrying loads independently of the steel girders, the two structural systems could be separated, and the latter could serve as a secondary safety system functioning only during overloading.
Discussion. The discussion that followed framed the dilemma facing the committee, namely that continued use of the bridge by loaded town maintenance trucks will create excessive stresses on the bridge, ultimately damaging the bridge's historic structural and material integrity. However, should the town's maintenance vehicle be unable to use the bridge, the town would be forced to select an alternative route that is six miles longer (three miles each way), necessitates greater changes in elevation, and hinders the town's ability to clear and sand roads in the vicinity of the bridge in a timely way for school buses when snow or ice collects. Although Route 7 would reduce the extra length of an alternative route, town officials choose not to use that road because of the volume of traffic and speed of that traffic.
Committee members then began a dialogue about the various other alternatives available for consideration.
Recommendations. Each alternative considered requires engineering analysis, and Scott Newman requested that he be given an opportunity to review the project for compliance with Section 4(f) and Section 106 before additional engineering analysis is undertaken. Specifically, VTRANS and FHWA must consider whether the additional mileage and concerns associated with the available detour makes that alternative imprudent for purposes of satisfying Section 4(f). Whether a site for a new bridge exists, and the comparative costs for that bridge, must also be considered. The meeting concluded with agreement to investigate those issues prior to further engineering analysis, and with plans to schedule a third meeting at a convenient opportunity.
Meeting Adjourned: 12:05 P.M.