The Kingsley Covered Bridge (Br. 28 on TH 39) in the town of Clarendon has been programmed for a project in the Town Highway Bridge Program. Laura Stone, Structures Scoping Engineer has worked with Hoyle Tanner & Associates to document the history of repairs and develop a list of alternatives for rehabilitation of the covered bridge.
Josif Bicja, of Hoyle Tanner & Associates, gave a PowerPoint presentation of the components of the covered bridge and associated needs. A summary of these concerns is as follows:
There is a metal roof on the bridge that is blistering and fading. The ridge cap is attached with nails and screws that may be starting to leak. Many roof boards are cracked. Trees are overgrown at the ends of the bridge covering the roof. There are splits and rotten sections of the roof rafters along with evidence of insect damage. There are also some broken members and over cut notches. There are guy wires attached to the ends of the covered bridge, but they are not well anchored.
There are large (1 ¼”) gaps in the lattice splices. Several lattice members have split ends. A considerable amount of rot was noticed and generally that indicates there is more rot in areas not visible. There is some racking and twisting of the top chord, with rot and insect damage present. The bearing timbers are rotted with some settlement of the truss evident.
The existing lateral bracing is not adequate to allow removal of the guy wires. The solution is to add additional bracing just below the existing or strengthen the cross beam to chord connection to handle the guy wire attachment. There is more than enough freeboard above the stream, therefore the guywire is not needed to anchor the bridge due to stream flow loading.
The runners are tapered to match the backwall as the backwall is lower than the finish grade of the deck. This in effect launches vehicles onto the bridge. There is also a considerable gap between the end of the deck and the backwall which traps material and moisture.
The nail laminated deck and floorbeams are in good condition and not planned for replacement. The deck can handle an H20 loading and the floorbeams are good for H15.
There are concrete abutments with evidence of cracks, spalling, delamination, and staining. The abutments are quite high at approximately 32 ft. in height. The abutments appear to be founded on ledge at the stream level.
There was a discussion about the appropriate design loading for this bridge. The consultant presented the affects to the trusses for the H3, H12, H15 and H20 truck loadings. The town mentioned the desire to maintain the existing 3 ton loading. A consensus was reached that the H12 (12 ton truck) would be an appropriate design loading. There is a small amount of additional lattice replacement (7%) above and beyond what is needed due to condition and approximately 20% of chord replacement to achieve the H12 loading. There is a significant increase in the lattice replacement needed to go to the H15 or H20 loading (+37%).
There was a discussion to modify the portal to reduce the opening to the covered bridge. The opening is currently posted at 11’- 0” and measured at 12’ – 1”. There was concern about changing the visual aspect that exists and the decision was to keep the portal as is.
There will be discussions with the Town on adding lighting to the bridge as there are no windows present and no interior lighting. Given that this covered bridge is 120 ft. long it is quite dark inside the bridge and difficult for drivers to see pedestrians.
Recommendations were made to add NOCHAR to selected members along with possibly installing Protector wire and a sprinkler system. These will be discussed with the Town also.
Meeting Adjourned 11:00 A.M.