Another Bridge Thread

[Luke'sScreenName]

Luke, I have pulled a couple trailers back there behind my quad, and I did take my truck back there a few times early on, but may need to clear a little on the path to get it back there again. I would plan on pulling the lumber on a trailer, either behind the tractor or my truck, even if I had to make a few runs. Is that what you are talking about, or do you have another idea?

Ya, you mentioned it would be difficult to get a trailer back there but thought maybe you were taking about and 18 wheeler size.
Seems like a cheap used equipment trailer (16-25 feet) set on concrete footings would be easy and cheap.

 

[Egon]

Egon, I don't know what section modulus figures are, but will go google them. I'm by no means an engineer of any sorts, which is part of the reason I'm here. I can generally teach myself things through research, but when faced with the alternative of having to pull my friends tractor out of a creek, I'll take as much advise as I can get. Design breaker seems important, so I'm off to google.

Thanks ag

I'm not an Engineer either. Also can't really give advice either.

Usually the deeper the beam the greater the section modulus the greater the load carrying ability. The object is to balance the beam design with the decking required to get an economical solution. This would also incorporated the use of lateral bracing between the beams.

One can also add flanges to a wooden beam. The other way is to make up a deeper beam from narrower flat pieces that are glued and do not have to be full length. This would be the desirable method and cover with fiberglass to slow rotting. Gluelam beam. (Buy them and the design might come with )

The point loads would refer to the tire contact spots where it might be a good place to place the beams.

Note: the beam formulas look nice but they have to be applied properly situation wise.

 

[mrtwister]

This is mine.... 20' X 8'......3 beams across creek- 8" X 8"X 20 ft (white spruce covered with tar paper to prevent moisture build-up and rot)).... supported by railway ties recessed into the creek-bank at each end.....3" decking ( white pine and jack pine treated with sealer)...underneath vertical support in the middle resting on bedrock on the creek-bed ( pressure-treated 8" X 8")...no problem supporting tractors and other vehicles...in the springtime the vertical support-beams sometimes wash away but we cross anyway....some deflection however not enough to worry about until they are replaced. Still going strong after 3 years.

 

[tennesseejb]

Thanks to everyone for your feedback. I will check into culvert before I making any final decisions. I agree it's the "easiest" and probably the "safest" solution, but what I want to avoid is having two or more smaller culverts and essentially have spots in the creek where debris will back up and the force of the creek after a good rain will possibly wash the culvert. If I was going that route, I'd want a full piece of culvert that fills the 8-10 foot creek opening. I'll check.

I can't get any commercial companies to come back there, but is possible to get (drag or roll) a trailer back there, I just haven't found one that felt big enough for the job for less than what I could build a wood bridge. I also like the idea of a wood bridge from an aesthetics perspective, but again, it's an option worth looking into further before locking in. What I didn't know about trailers is that often the ones pulling tractors have axles in the middle to support the load. In my case, the middle would not be supported. So I'd want to get one (like a semi flatbed or something?) that I know can hold the weights we are talking about. Could someone who is suggesting a trailer post a link to one that could give me an idea of the type of trailer we are talking about... just so I don't hear one thing and think something different than was was intended.

mrtwister that is essentially what I'm thinking except my span is only 10-ish feet and I don't want to put the support in the middle. That being said, given my span is half your's, it seems I would essentially be doing the same thing from a structural perspective. Seems that is much in line with the design kennyg has suggested. Did you just lay tar paper across the top of the beams before attaching the decking? and fold it over some to protect from rain? Or did you do something more to "wrap" them? Are the beams attached to the railroad ties? Or just sitting on top? Railroad ties instead of concrete seems like a good option as well. Fairly easy to replace later if needed. Did you choose 3" decking for a structural reason? Seems most have used 2x (really 1.5), but I haven seen more commercial bridges that used 2x6 (or 2x8) on it's short side to deck all the way across. Overkill for my application I think, but it did look nice. Seems it would be a pain to replace a few boards in that scenario though.

Thanks again to everyone.

 

[tennesseejb]

What about something like this?
38ft trailer

 

[Luke'sScreenName]

Or this? https://knoxville.craigslist.org/hvo/5369903988.html

 

[Luke'sScreenName]

Or #4 here. https://asheville.craigslist.org/hvo/5365189106.html

 

[LD1]

Couple of suggestions.

1. Trailer is quickest, easiest, and pretty cheap if you are patient and wait on the right deal. Do some serious CL shopping before you rule this out.
2. Look for steal beams. Some 12-15' steel beams in the 10"-12" depth range I usually see on CL all the time for next to nothing. Worst case scenerio you have to buy new beams. Around here that is ~50 cents a pound. Even something as small as a W8x21 beam has the ability to carry ~4500# point load right at mid span and still have a 5:1 safety factor. A 40' stick would be ~820# and with a few cut fees to whatever size you need would probably run under $500. Then all you need is decking. Probably a good bit cheaper than you $1000+ budget.

3: Contact your local electric companies and inquire about used poles. I did a bridge spanning only about 4' this way (but drove 18k backkhoe over it). Basically use the electric poles the same way you are wanting to laminate the 2x8's. Only alternate every other one, cause the poles are tapered, So have big end on near side, then next one have it on the far side, then back to near side, etc etc. Think like making a raft.

Electric poles are usually 8-10" diameters, and treated really well. The electric companies usually give away used and broken poles. Most times still in pretty good shape. But sometimes not, avoid the ones taken out of service for rot. But lots are just where they have moved a line for one reason or another, (they dont re-use poles no matter the shape), or some are broken from stormes or accidents. The broken ones are fine cause poles are 40' or so long, lots of times you can still get two good 15' lengths.

After you have all the poles laid out spanning the creek, lay down decking with some polebarn spikes. Decking over it ties everything together and keeps the tires from just "displacing" and rolling the poles out from underneath you.

My absolute last resort would be the all wood beam as you describe or a all wood bridge with wood beams and wood decking. Lots better (and cheaper) solutions out there. I dont like to mess around with heavy things crossing bridges, do it right.

 

[mrtwister]

mrtwister that is essentially what I'm thinking except my span is only 10-ish feet and I don't want to put the support in the middle. That being said, given my span is half your's, it seems I would essentially be doing the same thing from a structural perspective. Seems that is much in line with the design kennyg has suggested. Did you just lay tar paper across the top of the beams before attaching the decking? and fold it over some to protect from rain? Or did you do something more to "wrap" them? Are the beams attached to the railroad ties? Or just sitting on top? Railroad ties instead of concrete seems like a good option as well. Fairly easy to replace later if needed. Did you choose 3" decking for a structural reason? Seems most have used 2x (really 1.5), but I haven seen more commercial bridges that used 2x6 (or 2x8) on it's short side to deck all the way across. Overkill for my application I think, but it did look nice. Seems it would be a pain to replace a few boards in that scenario though.

Thanks again to everyone.

In reply to your question, yes I laid a long strip of tar paper maybe 14" wide, the length of the beam then folded it over along the sides then nailed it along those sides with roofing nails...you can kinda see it in the picture with the truck crossing.....then the decking was attached to the beams with 6" galvanized lag screws. I drilled a couple of 3/8" holes clear through the end of each beam then drove 12" spikes right through those holes to attach them to the ties. I milled the beams and decking myself with an Alaskan Sawmill so I could chose my own dimensions....I had the wood for free so I chose 3" thick to make sure there was little to no deflection when driving over it. Hope this helps...Twister

 

[Jim Timber]

A 24' 24" steel culvert costs about $400 around here. You could get a bunch of fill dumped where there's good access and build it up for well under your 1K budget. Class 5 is about $200 a 12yd truck delivered in my area, but we have taconite tailings which are better road base and won't wash out if crested, and those are $185 a load.