After reading about the gift of the Martin Bridge to the town: "Marshfield Makes a Deal", in the Barre-Montpelier Times Argus, John Weaver contacted George Longenecker, Marshfield selectboard chairman.
Weaver, a Professional Engineer and Bridge-watch Coordinator for the Vermont Covered Bridge Society, volunteered to evaluate the bridge at no cost. The following report was sent to the Town of Marshfield Selectboard.
The overall conditions of the dry rubble masonry abutments and wings are poor. In particular, considerable (river) undermining and settlement of the northwest and southeast corners are evident. Individual stones indicate noticeable dislocation and large open gaps between stones appear in many places at both abutments.
Overflow areas in adjacent fields seem to provide some channel flow relief during flood events.
The wood superstructure demonstrates some merits: The roof seems to be tight enough to keep most of the structure dry, also, it has ample overhang and pitch. The siding is in fair condition and provides venting at roof soffit locations. The superstructure shows some evidence of repairs and maintenance over the life of the bridge and still maintains a positive camber.
However the bottom chord indicates heavy areas of rot at the end diagonal joint locations and bearings. Due to this rot and settlements of abutment stones, the trusses have settled (distorted) and do not bear on the abutments in a satisfactory manner. The entire bridge is racking (very noticeably) toward the upstream side. Many truss joints are loose and distorted. The floor system is missing planks and the floor beams are spread very far apart. The queen posts seem to be connected to the bottom chords with metal straps - this was probably not the original design.
Judging from experience with Randall bridge in Lyndon, the cost of underpinning each abutment would be approximately $16,000. Rehabilitating the upper portions of each would probably cost the same, for a total abutment cost of $64,000. Repairing truss members, flooring, floor beams and aligning the wooden superstructure would probably cost approximately $25,000 - $30,000, for an overall total of approximately $94,000. It is recommended that all wood members on the inside of the bridge be treated with a surface application of fire retardant.
Per site visit the bridge appears to be salvable, that is, to rehabilitate it to some stable condition. However, even rehabilitated, the structure may have only somewhat limited load capacity beyond carrying its own dead load. Final use and load capacity would have to be determined by a professional engineer. For now, continued deterioration of the foundations will probably cause further distress in the wooden superstructure, leading to its eventual collapse.
John H. Weaver, VCBS