Author Topic: Bridge Timbers (Read 2360 times)

tyb525 · « **on:** July 05, 2008, 09:11:43 pm »

I'm going to build a light-duty bridge across one my creeks so i can get back to the woods with my atv and trailer. (can get thru the creek with atv but not trailer). It needs to be able to span about 15' and hold an atv and a garden-tractor wagon full of firewood. I'm gonna use pallets for the top, but I'm not sure what to use for the supports.

Will tulip tree timbers (about 10" diameter) be strong enough? Or would you guys suggest something else.

I'll be thankful for any advice or tips.

Onthesauk · « **Reply #1 on:** July 05, 2008, 10:18:02 pm »

I built two of these last year for exactly the same purpose. I had some Western Red Cedar, broken off up about 40 feet by a falling alder, that I salvaged for the longer one, (16 foot.) Cedar was about 16 inches where I cut it off and about 10 inches at the smallest end that I used. Decked it with treated 2X6 and holds the ATV and a full trailer of firewood with no trouble at all. Shorter bridge is 12 foot, slightly smaller cedar, but done the same way. Tacked a 2X4 on each edge just to make sure nothing slid off.

Don P · « **Reply #2 on:** July 05, 2008, 10:26:11 pm »

Locust or white oak would be a more durable choice. Tulip poplar? If so it will rot really fast exposed to the ground.

This calc would do the job for sizing with a couple of caveats. First a rolling load should be doubled to account for its dynamic nature (brakes and a nosedive, bounce, etc.). You should be able to inscribe the square beam within the small end of the round timber to be safe.
http://www.forestryforum.com/members/donp/beamclc_ctrpointload.htm

If you can get one of those 2 species then I'd use these numbers for wood strength (grade em tight, no big knots, nasty grain etc),
Fb=1000
E 1.0
Fv 200

All that said I crossed a low gulley about 14' span on a pair of 6x8 locust for several years with about a ton. Never have checked it.

OK just did, I'm apparently dead

tyb525 · « **Reply #3 on:** July 05, 2008, 10:39:18 pm »

I have the tulip logs handy so i thought just maybe...

Would they get me through the rest of the year? I don't really want to use white oak or locust for a bridge, but I do have a lot of locust around here.

Don P · « **Reply #4 on:** July 05, 2008, 10:46:23 pm »

they would last the year, I'd be leery of crossing them next year though. When they go it'll likely be a brash (short grain, little tear) failure... pop, boom

Mooseherder · « **Reply #5 on:** July 06, 2008, 12:32:30 am »

We torched the axle off an old truck frame, dragged across the creek, put stringers across, then pallets on top. I pounded a couple steel rods down where the frame allowed into the ground.
I don't know how it is still there because it is under flowing water a couple times a year. It was under water last week again.

Don P · « **Reply #6 on:** July 06, 2008, 07:59:08 am »

If it will get covered occassionaly tip it upstream a little so the stream pressure will hold it down rather than floating it off.

Ironwood · « **Reply #7 on:** July 06, 2008, 09:19:51 am »

Man if it were me I would DEFINETELY go with white oak or locust. If your putting your labor into it why redo it in a year or two? IMHO. Your greatest expense should be YOUR labor.

Ironwood

tyb525 · « **Reply #8 on:** July 06, 2008, 10:17:12 am »

Well I have plenty of both so maybe I'll go with that. With that said how big should they be? Should I peel the bark off?

Ironwood · « **Reply #9 on:** July 06, 2008, 04:37:22 pm »

I am no expert, so take this as you will. Sapwood lacks the bug resistance of the heartwood. While the tree is alive the living layer is protected by pesticides in the nutrients that flow up the tree, once dead the sapwood is the first to go leaving behind the much more durable heartwood. I would try to get the sapwood cut off or just cut it away with a chainsaw at the joint areas and let it rot away elsewhere over time v
ironwood

SwampDonkey · « **Reply #10 on:** July 06, 2008, 05:00:39 pm »

Some tamarack/larch or hard pine might work to. Most small woodlot owners around here find an old truck carcass like mooseherder suggested.

tyb525 · « **Reply #11 on:** July 06, 2008, 10:00:22 pm »

thanks for the tips guys, I found a couple I-beams behind our barns that should do the trick. I didn't really want to cut down a good oak or locust.

woodmills1 · « **Reply #12 on:** July 07, 2008, 07:25:08 am »

Now that you found proper metal beams for your bridge, why not cover it with proper 3x4 or 4x8 instead of pallets?

tyb525 · « **Reply #13 on:** July 07, 2008, 05:14:49 pm »

I just might do that. How should I fasten them to the beams? Bolts?

WH_Conley · « **Reply #14 on:** July 07, 2008, 09:14:07 pm »

Bolt a runner to the top of each beam and nail the cross boards. By the way, get plenty of Ben Gay, or other preferred treatment.

tyb525 · « **Reply #15 on:** July 07, 2008, 10:20:58 pm »

Got me an old can of repellent, it would probably be illegal to sell it now, I think it has a lot of deet. It seems to work well.

Radar67 · « **Reply #16 on:** July 07, 2008, 10:33:40 pm »

WH, At 18, I don't think he will need any Ben Gay for sore muscles.....

tyb525 · « **Reply #17 on:** July 07, 2008, 11:03:56 pm »

I already do plenty of firewood cutting and misc farm work. I don't think I've ever had to use the stuff

Ron Scott · « **Reply #18 on:** July 07, 2008, 11:40:23 pm »

Looks like you're on track to making a long lasting bridge.

Good Feller · « **Reply #19 on:** July 12, 2008, 10:41:20 pm »

I wouldn't use white oak, pallets, etc. if you want it to last. If you are going to put in the time and sweat build it right. We needed a bridge just like you described for taking our four wheeler and lawn mower over too. The first bridge we built out of white oak logs and it didn't last very long,,,, 5 years maybe. So then we tore that mess down and used rail road ties. If you can get a hold of some long ones that's what you need.

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Author Topic: Bridge Timbers (Read 2360 times)