The snowmobile club has a bridge over the Burnshirt river in Hubbardston, MA. It's an old railroad bridge, supposedly from 1910 or so, that is re-decked for recreational use. It's about 30 feet long and 14 or so feet wide. The deck was last replaced about 9 years ago with oak and had significantly deteriorated. Since the bridge is on my new grooming route I had an especially interest.
The frame of the bridge is monstrous, four, 53" tall I beams. Those will easily support the grooming machine and since they're spaced about where the tracks of the machine go I wasn't at all worried about the machine going through the bridge. I wasn't even particularly worried about snowmobiles since their weight is so spread out. What really worried me (and the club as a whole) was dogs or horses. This is a multi-use trail so we need to watch out for everybody.
The state Department of Conservation and Recreation (DCR) had condemned the bridge and to be honest they were right, there were holes that had been roughly patched and a bunch of the decking was ready to let go at any time.
So how do we replace this deck in a way that ensures we won't have to do it again in a couple years?
Step 1: Pressure treated wood
55 6"x8"x12' planks. They weigh 140# apiece!
Step 2: Spacing
The old deck had the planks tight up against each other, we left a 1/2" gap between each plank.
In this picture you can see a board laying across the decking planks with a bolt hanging down, that bolt is one of the spacers.
To get a 14 foot wide bridge with 12 foot planks we offset each plank by a foot which left a gap at the end, this will help the bridge shed water off the sides.
We also way overbuilt the railings, the old bridge had 2x4 railings, these are 6x6s lagged to the bridge planks. You can't see them but above the planks there is another 6x6 between each upright, that plank is lagged down and then the upright is lagged into it. Those side rails are STRONG.
The whole job took 2 full days with 10-12 people each day.
One of my jobs was to organize removal of the old bridge, we took 7 pickup loads out, these were very heavy loads, the old wood was terribly water logged. Ben has been burning it in his outdoor wood boiler, it looks like the deck will heat his house for a full month. He cried about taking a day off work to help with the construction but I think he got a pretty good return on his investment.
