Rough cut lumber bridge deck

nay-aug · July 16, 2009, 07:32:41 AM

Hello All,

This is my first post!

I'm building a bridge over a creek that will span 28". Concrete footings on both sides and telephone poles for the main beams. I'd like to use 2 1/2" or 3" rough cut lumber for the deck boards, but I have no idea what wood would be best or thickness. A local sawmill suggested Beech, saying that is a hard wood that will last. They even tell me they can have it Wolmanized for an additional 20 cents per board foot. I looking for help on lumber type, thickness, wolmanizing, and even the use of telephone poles for the main beams.

This is a acess road to my camp and will see normal vehicle traffic.

I'm a total rookie at this, any and all comments welcomed.

Best regards, Al

jdtuttle · July 16, 2009, 08:02:03 AM

28 inches or 28 feet? ;D ;D. If it's 28 feet that's a pretty long span for a pole that was meant to stand straight up for loads. Maybe someone with an engineering background will chime in. What's the width of the bridge & how many poles do you have? This is a great place to do a little research :P
jim

nay-aug · July 16, 2009, 08:15:51 AM

Hello Jim,

Thanks for replying. Yes, it is 28 feet. I was planning on using 4 or 6 poles, because I have them available. They are 8" to 9" in diameter. I could purchase some rough cut timbers if that would make a better bridge. Deck width will be 12'. I'm wide open on this project and looking for suggestions.

Any thoughts on the deck boards?

Regards, Al

jdtuttle · July 16, 2009, 08:30:15 AM

http://www.bridgesite.com/funand.htm
Check out this site. You will need to do load calculations of the vehicles that will be traveling over the bridge. 9" poles spanning 28' may not be adequate without some type of truss or suspension design incorporated. Know any engineers that can calculale loads?

jim

Brad_bb · July 16, 2009, 09:02:18 AM

If you are planning to put vehicles over it, I don't think you will be able to lay down poles and nail deck boards down to them. It will take some real design (trusses) and joinery. Beech is a great hardwood for a timberframe if it's good quality, but it's not rot resistant. Probably White oak for the structure. Deckboards options are up to you, depending on the upkeep tolerated, amount of use, etc. I'd consider if you really need 12 ft wide. You can do it, but 8 feet would be less load and a little easier on the design.

pineywoods · July 16, 2009, 09:19:53 AM

Go to my photo gallery, there's pics of just such a project, just a little shorter. There's posts on here somewhere, do a search on building a bridge. I used 6 6X12 pressure treated pine, deck is full 2 inch heart pine, pressure treated. Look down the left side of the screen, there's a little red toolbox. click on that and scroll down to DonP's calcs. There's formulas there for calculating load bearing loads for solid beams. You can get away with deck nails to fasten down the deck, just use big ones. We run a dozer over ours and it ain't fell in the creek yet ;D ;D I don't think the poles will do the job. Whatever you use, make sure is treated against rot..

nay-aug · July 16, 2009, 10:01:47 AM

Thanks Gents,

Great comments on the main beams, I'll do the calculations and rethink these beams.

Any more thoughts on the decks boards. What lumber would be rot resistant? I'm planning on having it treated as well.

Best regards, Al

DanG · July 16, 2009, 10:22:05 AM

Hey Nay, and welcome to the forum.

Is there any way you could put some intermediate pilings under there to shorten the span, or is the actual stream 28 feet wide? I'm thinking even if you could place them four feet from each end you would cut the span to 20', and some well made knee braces would shorten it even more.

nay-aug · July 16, 2009, 10:36:00 AM

Hello Dan G,

Yes, on the one side I can get additional support and shorten the span to 19 or 20 feet. I'll do the calculations as someone else has suggested.

Any thoughts on the deck board material?

Best regards, Al

MSU_Keith · July 16, 2009, 10:37:42 AM

A publication that helped me greatly is the timber bridge document located here:
http://www.fpl.fs.fed.us/products/publications/pubs_interest.php

It has descriptions of all the various calculations needed to design simple and more complex bridge structures including static and dynamic loads, flex limits, shear limits, abutment requirements, etc.

My span is 12' with 5 - 12" x 8" x 15' WO timbers connected to poured 12" round piers. Decking is 2" WO in the middle with the entrance and exit 'ramp' decking wolmanized. Side beams have a truss/railing that also provides support.

DanG · July 16, 2009, 12:58:49 PM

Quote from: nay-aug on July 16, 2009, 10:36:00 AM

Any thoughts on the deck board material?

Without knowing where you are, it's hard to know what might be available. Basically, anything they use for RR ties should work. The beech should be fine if you have it treated, as mentioned. Also, sycamore and sweetgum are known to take treatment well.

I'm also thinking, if you have a creek and need a bridge, you also might have some trees. You could save a big roll of cash by cutting your own and hiring a sawyer to make your beams. ;)

nay-aug · July 16, 2009, 01:28:34 PM

DanG,

I live in Northwestern Pa., about 60 miles north of Pittsburgh. The parcel of land I'm talking about has a good stock of trees, mostly Maple. I think Silver Maple! How would that be for main beams and deck boards?

The guy with the Beech quoted me 60 cents a board ft. for 2 1/2" thick x 8", 10" & 12" random widths. I need enough to cover approx. 28' long by 12' wide. Plus another 20 cents per board ft. to pressure treat it. I didn't think that was too bad.

Regards, Al

DanG · July 16, 2009, 01:43:42 PM

I can't answer your question about the maple, but there are plenty of folks here that can. ;)

80 cents isn't a bad price at all for the p/t beech. All I'm saying is, you could get it even cheaper if you wanted to use your own trees. You wouldn't believe how many people have ended up with their own sawmill after having some custom sawing done. Just planting a few seeds for thought. :

;D :D

jdtuttle · July 16, 2009, 03:02:25 PM

I'm in NY and have sawn white oak for bridge deck boards.
jim

Brad_bb · July 17, 2009, 10:47:22 PM

Silver Maple, no good for beams or much of anything else. It's soft and not very strong. White oak is, of course one of the best choices due to it's resistance to rot and strength. You don't need to treat it. If you are trying to do a really nice job of it, keep it from touching the concrete pilings. Use something as a barrier between them to keep moisture off the beams.

Meadows Miller · July 18, 2009, 06:24:10 AM

Gday

Welcome to the forum Nay-aug You have come to the rite place Mate ;) ;D ;D 8) 8)

With the poles overhere H/wood to span that distance on a Major/minor road is about 16" to 18" dia midpoint or the same size in a hexagon with the sapwood removed they are fun to saw :

4 of them will cope with two semis hitting it at 62mph at peak load ;)

Quote from: DanG on July 16, 2009, 01:43:42 PM
I can't answer your question about the maple, but there are plenty of folks here that can. ;)

80 cents isn't a bad price at all for the p/t beech. All I'm saying is, you could get it even cheaper if you wanted to use your own trees. You wouldn't believe how many people have ended up with their own sawmill after having some custom sawing done. Just planting a few seeds for thought. : ;D :D

DanG We arnt leading another bloke astray are we Mate ;) :D :D ;D Its pretty simple math to us ;) :D Want Brige + Have Trees = Buy Mill , Learn how to use it Here ;) , Mill timber and Build Bridge and the most important part ;) Keep Mill for other projects Does That sound about rite Mate ??? ;) :D ;D

Reguards Chris

tyb525 · July 18, 2009, 10:36:45 AM

Chris your reasoning is flawless ;)

SwampDonkey · July 18, 2009, 05:49:28 PM

Can you use an old truck frame and use beech or white oak as decking? Grandfather always used white ash on his bridges. I mentioned the truck frame because they use them around here, probably not longer than 16 feet however. Anyone got an old junked logging trailer frame? I seen one the other day on a vacant lot that would span that creek. ;D

Rooster · July 18, 2009, 07:40:05 PM

Al,

Welcome! I am also fairly new to this forum. And I have to say that the members here that post regularly are very supportive and also very practical. I see that you were having a hard time getting these guys to chime in on a suitable decking material. And all the replies were focused on your choice of support structure. It makes sense when you think about it, they are just trying to steer you in the right direction. The best decking choice in the world is not going to help you any when it's laying in a pile at the bottom of your ravine. ;)

Also remember that there are a lot of FF members who have't seen your post yet, who might be able to answer the rest of your questions..just give it some time.

I also saw a farm bridge made out of a couple of used flatbed semi trailers, side by side.....and they were decked with White Oak. ;D

Good luck, and keep asking questions, these guys are the best!

Rooster

sbishop · July 19, 2009, 06:28:13 AM

Swampdonkey, i've seen them use an old school bus frame!

Sbishop

Meadows Miller · July 19, 2009, 08:02:47 AM

Gday

Quote from: tyb525 on July 18, 2009, 10:36:45 AM
Chris your reasoning is flawless ;)

Gday Ty Great minds think alike Mate ;) :D :D ;D Hows the Lt10 going are you getting abit off sawing done ??? or ar things busy with school mate ;) ;D 8)
I Also told Woodmills the other week you would have no dramas doing a strait swap on the lt70 with him seen as he reckons shes alittle quick

;) :D :D :D :D :D :D

Another thing to think about is a rail car container flat usually come in 20' 24' 28' and 40' lengths alot of farmers overhere use them as main access to farms you can drive a loaded semi over them ;) Ive also seen a flat car used at 60' long but that was abit of a tight sqeze getting a semi over as he had a tight bend at each end :

Reguards Chris

tyb525 · July 19, 2009, 08:13:28 AM

Hey Chris,

I'm getting some done on the little LT10 but I'm not setting any records :D Schools been over since June 1 but I've had other things to do such as build mom a neck deck ;) I would not mind having that LT70. Then I would need my own crew to keep up! ;D

Sorry for hijacking the thread :D

nay-aug · July 20, 2009, 09:25:56 AM

Well all the comments have been very helpful. I originaly though about a old flat bed truck as well, but his is a tough area to get to. What ever I use will need to come in via pickup truck, Polarus Ranger, or dragged in by a small Komatsu dozer. Oh yeah, it's pretty steep too!

I'm going to use timbers and/or poles for the main beams, and shorten the span to 20' via an intermediate support. Now I just need to solve the deck material choice. Sounds like White Oak is the best choice, not sure about the cost or availability of that. The Beech was economical @ 60 cents a board ft., but that would have to be treated. Silver Maple is no good, are there any Maples that would be acceptable? How about sugar Maples?

Regards, Al

Tom · July 20, 2009, 09:38:31 AM

If you are going to buy the material, there would not be anything wrong with treated pine for a deck. It would probaby be the most economical commercial solution. Something thicker than dressed 2x material would be better though. Pine is a good building material, light, strong, wears fairly good, available and is one of the less expensive.

Brad_bb · July 20, 2009, 10:51:06 AM

If this is to be a longterm solution, and used a lot, I'd go the white oak direction. but for a shorter term solution or doesn't see so much traffic, pine would be fine. Also consider the structure underneath so that the deckboards are adequately supported. If you had just two supports and the deckboards spanned 10 feet and you put weight in the middle, well you can guess what could happen. If using 2X deck of pine, think about the spacing needed for floor joists, now consider that you'de be driving heavy vehicles over it. That is why we have focused on the structure first. The deckboards shouldn't be doing much supporting, but rather the structure should, hence our focus. Were you planning to place the poles solid across? Like 10 or more poles side by side? If that were the case, we could calculate the static carrying capacity. You'd then need to use a considerable safety factor as dynamic loads could be significantly higher.