Present at Meeting:
Project engineer Wayne Symonds had previously prepared a proposed scope of work (SOW)/ assessment report for the rehabilitation of the Gorham Covered Bridge under project number Proctor- Pittsford BHO 1443(37) which was distributed for comment and review. In addition, Mr. Symonds prepared a power-point slide presentation to clarify some of the ensuing discussion. The ensuing notes are to be read in conjunction with the assessment report as the committee discussion generally followed the same outline as the report, as follows:
General introduction to the bridge and its history: The work performed during rehabilitation projects in 1956 and 1979 was detailed as well as the towns expressed desire for emergency vehicles to be able to cross the bridge. It was assumed that the bridge should be capable of a 40,000 lb. operating capacity, which would represent the maximum, occasional loading that the bridge could support.
Roof System: There was general agreement that the present corrugated metal roof can be replaced with a new, galvanized standing seam metal roof and that roof boards can be replaced as necessary. The roof rafters appear to be in good shape, but it was recommended that they be replaced, to be able to provide an approximate 18" overhang, with new rafters of a similar size and material. There is not currently any roof overhang and it is felt that water is currently running into the structure; to support this, the current lower top chord shows evidence of rot. Recommendations relative to tie beams and cross bracing are detailed in the proposed SOW -- there wasn't any disagreement relative to these areas so the project engineers can proceed as recommended.
There was a lot of discussion relative to the section on knee braces. They have been augmented with steel angles that are bolted to the middle of the lower top chord and to the tie beams. The SOW recommends that the steel angles be removed and the knee braces all be replaced with like material while modifying their configuration so that they intersect with the top of the lower top chord rather than at the bottom of the lower top chord. It is envisioned that this new design will be much stronger. One unusual current design feature is that the chord is notched at its intersection with the bracing rather than the bracing being notched. Eric Gilbertson, while acknowledging that the proposed configuration may be much stronger and effective, requested that the original configuration be re-assessed and consideration given to either supplementing the existing knee bracing and/ or improving the connections rather than replacing the original material and changing the original design. Structures agreed to examine this further. No objections were voiced over removing the auxiliary steel angles.
Truss System: No objections were raised relative to the discussion and recommendations for the top chords. With the exception of 6 lattice members at each end of the structure, it is recommended that the current members and current splices be assessed and replaced with similar size and material as needed depending on current condition. Approximately 70% of the members have been spliced. Plates on 2 of the splices will be removed and examined over the next few weeks as representative samples of their general condition. It was agreed that if original material in non-spliced sections has been damaged, the entire member can be replaced. If just the spliced area has evidence of damage, it can be replaced. For 6 lattice members at either end, the SOW recommends that the wood species be upgraded for greater strength, hopefully keeping the sizes the same.
Replacement of the lower bottom chord with glulam was proposed along with replacement of the upper bottom chord with southern yellow pine or Douglas fir. It was proposed that the first priority would be to replace current members with new ones of the same size. If not found to be sufficient, the second priority would be to investigate using members of the same width but deeper, depending on ensuing analysis. Eric Gilbertson expressed his preference that both chords remain the same size as present, even if this means using glulam for both chords. Recommendations are made in the SOW relative to the deck, but further investigation will be made in this area. Use of sawn lumber planking and glulam will be two of the options considered.
It was generally agreed that the current siding, none of it original, can be replaced with new siding. Representatives from the town expressed their preference for hemlock to be used. There was also discussion relative to extending the siding to cover the upper top chord. The town representatives stated that they would like to see the current opening remain.
Floor System: It was proposed that glulam floor beams be used to reduce dead load. Eric Gilbertson expressed that he would rather not see glulam used, but would not object if found to be necessary as the floor system is not original and generally viewed as expendable. Recommendations relative to removing distribution stringers, installing bolster beams to distribute loads and deeper bearing blocks were favorably received. In addition, installation of new cross bracing under the bridge will be considered.
Substructure: The SOW recommends constructing 2 new cast-in-place concrete abutments for reasons noted in the report. No strong objections to this were voiced. Hydraulic concerns were discussed. A longer bridge would be ideal, but is obviously not feasible. The concrete toe wall that was added in the 1979 rehabilitation project has resulted in increased constriction of the waterway. New abutments will help to resolve this. The use of form-liners and/or new stone abutments on concrete footings was discussed and will be considered. Scott Newman, in discussion following the meeting, requested that facing the new abutments with some of the original stone be investigated.
Dave Hoyne asked if there were any goals relative to the bridge's camber. As new abutments will likely be constructed and the bridge removed temporarily, 6" to 8" of positive residual camber will be strived for.
Monies were received from the National Historic Covered Bridge Preservation Program to rehabilitate this bridge, but one of the conditions is that construction funds are obligated by September 30, 2002. Therefore, project development is on the fast track. Accordingly, there will not be a formal preliminary plans submittal. It was agreed that the project engineers, after further analysis incorporating input from the town and Historic Covered Bridge Committee, will prepare and present a typical bridge section for further discussion by the committee at the appropriate time.
The efforts by the project engineers to provide comprehensive material for committee review was acknowledged and very much appreciated.
[This article was originally posted February 13, 2002]