Here's what the short span bridges will look like for our singletrack project. It's all wood construction. I'm using five inch (5") diameter treated fence posts as the vertical supports. 2 - #2 SPF 2 x 10's span between them. And #2 SPF 2 x 6's are the deck. My engineering calcs suggest this will span up to ten feet (10').
I plan to bolt through the 2 x 10's and posts with two (2) three-quarter inch (3/4") diameter bolts. The deck will be fasten to the stringers with sixteen penny (16d) ring shank nails.
If I remember, I'll take pictures of this before, during, and after construction. In addition to the bridge proper, I'm placing seven feet (7') of board walk on each end. Why seven feet (7')? Well, the smaller treated wood fence posts we can buy are three inch (3") diameter and seven feet (7') long. I'll lay these flat on the ground, two feet (2') apart. I'll span over these the #2 SPF 2 x 6's cut three feet (3') long. This is a pretty economical way to get some long lasting, but strong, board walk.
Ride on.
4 comments:
14" overhangs on your construction? I'd think a siginificant rider load on the edges of that overhang might compromise the fastening of the 2x6 not to mention the vertical rigidity of the 5x5 fence posts depending on how deeply they are dug in. Just my .02. I'm no bridge engineer... LOL
I get (2'-6" =) 30" - 1.5" - 5" - 1.5" / 2 sides = 11" overhangs. But, I have the same concern. I'm going to see how this goes. If things get loose or not work so well, I'm going to decrease the cantilever distance one of a couple of different ways.
I always have a plan "B!"
Oops, I went 36" on my figure. Either way, it seems to be a lot of leverage on a single post sunk into dirt (or even mildly concreted in place). I like the design of it, but maybe 2 posts spaced at 18" from each other with a single cross buck would work decently with very little additional material cost. PS- our trail groups agreement with the city is that we'll build/maintain the track, but they provide us raw materials (like lumber) when we need them. Might be a future consideration when negotiating additional trails/areas.
I can't think of any of our bridges that are supported in the center. They just span the full gap. Speaking of our bridges, when you going to roll down this way and ride some singletrack with me?
The posts are 7'-7" apart. I'm digging a 12" diameter hole, putting a 5" diameter post in it, three feet deep, and then saccrete. The 2 x 10's run on either side of the posts and then the 2 x 6 span perpendicular across. It will make more sense when I install it and take pictures as I go.
I am stuck here every single weekend until this project is done. Once it is complete, I'll be looking for things to do and places to go. Looks like fall trips are in order.
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