Historic Covered Bridge Committee Notes of March 2, 2006 and April 5, 2006 for:
BRALEY COVERED BRIDGE (#38) IN RANDOLPH
March 2, 2006 Meeting
Present at Meeting: Committee members Warren Tripp, Nancy Boone and Sue Scribner. Also in attendance was Joe Nelson representing the Vermont Covered Bridge Society, VTrans project manager John Weaver as well as several members of the consultant team – Steve Hodgdon of VHB, sub consultant Phil Pierce and master stone mason Michael Weitzner. Mark Sargent, Chris Williams and Rob Young of the Structures Section also participated in the meeting.
Steve Hodgdon of VHB gave a PowerPoint Presentation outlining the existing conditions at the bridge site along with some of its history. This provided information in addition to that provided in a Structure Rehabilitation and Alternatives Assessment Report of February 6, 2006 that had previously been distributed to committee members.
The consultant team did a good job presenting their material in relationship to the Historic Covered Bridge Preservation Plan and its Priority of Treatments and Priority of Uses. Superstructure recommendations are as shown below. The consultant recommends that steel beams remain under the bridge if emergency vehicles are to use the structure; the bridge provides the only access to several homes so this is necessary. A summary of the recommendations for the superstructure is as follows:
- Repairs and or replacement of individual members as indicated in the diagrams below. All replacements to be of same dimension as original.
- Retention of all metal rods
- Replace siding in-kind
- Apply fire retardant
- Retain collar ties
- Paint knee braces to enhance visibility
- Replace floor system with new galvanized, painted steel beams of slightly shallower depth to increase hydraulic capacity with nail laminated wood deck
- Install timber curb along edge of deck and raise trusses by approximately one foot to provide additional vehicular clearance to minimize impact damage
- Approach rail at all four corners
The presentation also included discussion on the substructure. The abutments are in very poor shape; the abutment at the west end is in critical condition with many voids. There is consensus that the existing abutments cannot be saved. Therefore the discussion moved on to whether the existing abutments will be replaced with new laid-up stone abutments or with concrete.
Mr. Weitzner was present as a professional member of the Dry-Stone Walling Association of Great Britain and has extensive experience with laid-up stone structures. Mr. Weitzner reported that he would be cautious about using the same type of stone as is there presently (schist). He would want to ensure that settlement will be uniform, i.e. spread out evenly. He recommends using larger stone at the bottom courses as they would be a lot stronger. Pros and cons on masonry abutments were detailed as follows:
- Stone has long term durability
- Stone would be in keeping with historic fabric
- Stone would be more aesthetically pleasing
- Stone abutments would cost approximately $50,000 - $60,000 more than concrete
- Stone abutments would require use of a skilled mason to ensure work is constructed properly
- A consistent stone source might be difficult to find for the size of stone needed.
For concrete abutments, pros and cons are as follows:
- Typical construction for bridge contractors
- Can be constructed with vertical face to increase hydraulic capacity
- Smaller footprint at a site with tight constraints
- More formwork and "in the dry" construction required as well as curing time for each concrete pour
- Aesthetically not as pleasing.
A lot of discussion followed on the specific site conditions that exist.
A motion was made as follows: The committee accepts the recommendations for the concept and scope of the covered bridge rehabilitation and recommends that the replacement of substructure with either stone or concrete be left to later. Further, it was recommended that the project manager pursue a phased project, i.e. that a temporary bridge be installed as soon as possible and the trusses removed. The one exception to the consultant’s recommendations is that the committee would not like to see the knee braces painted.
The motion was seconded and passed.
April 5, 2006 Meeting
Present at Meeting: Committee members Mike Hedges, Eric Gilbertson, Bob McCullough, Pam Thurber, Warren Tripp, Nancy Boone and Sue Scribner. Also in attendance was Joe Nelson representing the Vermont Covered Bridge Society, Mike Canavan of the Federal Highway Administration, Joe Voci from the Town of Randolph, VTrans project manager John Weaver, Steve Hodgdon from VHB and Lee Goldstein of the VTrans Environmental Section.
Steve Hodgdon had another PowerPoint Presentation on the substructure. Currently there are large voids, evidence of settlement, the caps are only partially supported and there is evidence that there is some tilting and/or sliding of the abutments. Over the years, the grade has been raised 3-4 feet which has added stress to the substructure.
Many of the same "pros and cons" as were discussed at the previous meeting were discussed again. However, using figures provided by the stone mason and using more accurate quantity estimates, the consultant now estimates that a stone abutment would cost $200,000 - $250,000 more than a concrete abutment. The consultant recommended use of concrete, primarily on the basis of cost savings and that it would be easier to install at the tight site that is present. Use of a stained dry stack form liner was recommended.
To expand on the "tight site" discussion, the consultant has determined that concrete abutments would have a smaller footprint and could accommodate approach rails on the wings. Further, the wings can be built to "fly" off the main stem wall with a single footing. Concrete would also provide for the greatest hydraulic opening. The bend of the river does provide some physical constraints on one side of the bridge; installation of a temporary bridge provides physical constraints on the other side.
The stone mason recommends use of much larger blocks of stone -- about 2' x 4' at the bottom courses, extending at least as far into the abutment. Therefore, the appearance of a new laid-up stone abutment would be very different from the existing abutments. Further it is proposed that the footings and cap would be of concrete regardless of what the remainder of the material used will be.
Lively discussion followed. Some basic points brought up include: the bridge has a concrete deck and steel beams, a new stone abutment would be very different in appearance both in its size and the stone used, there will be a fair amount of concrete used either way as it is proposed that the footings and caps be of concrete, form liners are not desired, no old fabric would be saved if new stone abutments are built, the cost differential is fairly significant. Some discussion followed as to whether to include bid alternates to see how much more stone abutments would cost.
The following motion was made (with some reluctance): "Motion to replace laid-up stone abutments with colored concrete with chamfered edges. Basis for motion is that there is going to be a large amount of concrete for the footings and caps. Rather than a reconstruction, a new stone abutment would be a change in stone type and size. Also, the site conditions favor the use of concrete.
Committee members and the Town voted. All committee members voted in favor of the motion. The Town representative voted against motion -- stating that he would like to see stone used and include bid alternatives in the Invitation for Bids. The Vermont Covered Bridge Society representative stated that they would like to see new stone abutments built. Motion to replace stone abutments with concrete had the majority of votes (7 versus 1).
The committee would like to thank the consultant, VHB, for their thorough presentations. As well, we would like to thank the Town of Randolph for sending a representative.
Chair, Historic Covered Bridge Committee