# Need to build a 25' flat bridge



## Vedder316 (Oct 1, 2011)

I have scoured the net for plans to build a 25 foot flat bridge i need to take my riding mower over a creek with no luck. My mower is an average craftsman yard mower. I was thinking on doubling 2x12x16's up and connecting them length wise. (x2 on the outside and single connected ones in the middle) as the main supports. What would be a safe way of connecting the 2x12x16's length wise? Do you think that would safely support the weight? Below is how I was thinking on laying out the 2x16's. I would however need to connect them length wise. Would this work? Any help or suggestions would be great. Thanks. ***Edit. I will likely have x2 of the 2x16s in the center instead of the 1.

Matt


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## Jackofall1 (Dec 5, 2010)

Hello Matt and welcome the best DIY'r site on the web.

You could try this link http://www.fs.fed.us/eng/bridges/documents/2x12/R9_STD_Trail_Bridge.pdf and http://www.fs.fed.us/eng/bridges/drawings.htm

Just remember you build it you are liable for it, someone gets hurt and its your butt they will be dragging into court.

Mark


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## Willie T (Jan 29, 2009)

The cheapest safe way for you to accomplish this is to go to a truss manufacturer.
Have them engineer and design four (4) 30 foot, flat top trusses - two, doubled, for each side of the bridge - about four feet apart. Tell them you are thinking of "Pratt" trusses... or possibly "Lattice" trusses.
There's a possibility they will tell you that you will need six (6) trusses instead of just four (4). Not likely, but possible.
Put these in place on concrete piers or 'seawall' structures on each side of the creek, spanning the creek.
Then just build a roadway between the truss girders.
This will give you a bottom to drive on and sides to act as safety rails. Make the trusses high enough, and you can put a roof on and enclose it like a covered bridge if you want to.

BTW, built as you drew it, there's not a snowball's chance in hell it will work.


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## Joe Carola (Apr 14, 2006)

vedder316 said:


> i have scoured the net for plans to build a 25 foot flat bridge i need to take my riding mower over a creek with no luck. My mower is an average craftsman yard mower. I was thinking on doubling 2x12x16's up and connecting them length wise. (x2 on the outside and single connected ones in the middle) as the main supports. What would be a safe way of connecting the 2x12x16's length wise? Do you think that would safely support the weight? Below is how i was thinking on laying out the 2x16's. I would however need to connect them length wise. Would this work? Any help or suggestions would be great. Thanks. ***edit. I will likely have x2 of the 2x16s in the center instead of the 1.
> 
> Matt


omg!!!


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## Willie T (Jan 29, 2009)

I think it could all be summed up with these emoticons: :wheelchair::bangin::w00t:


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## 1910NE (Sep 5, 2010)

If I was attempting this, I would look at a shallow arch of some kind as the way to go.....pics would help.


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## Willie T (Jan 29, 2009)

ddawg16 said:


> Look into PSL beams....you can get them over 25' long. Hint....your not going to find them at Home Depot.
> 
> Based on the span tables I have...2 PSL beams...3.5 x 11.25 at 25' long....would do just fine at holding the weight of a riding lawn mower (not a tractor) and the average adult....you would of course need proper blocking and footings....


The single beam in your garage is 20' long (7" x 16")...it cost you about $600.... Right?

That might get pretty expensive for this bridge... and then you still really should put side railings on it.

The trusses might give you everything for a bit cheaper.


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## BigJim (Sep 2, 2008)

I would use telephone poles but one thing is for sure, what ever you use it is best to secure it so it don't wash away at high water.


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## Daniel Holzman (Mar 10, 2009)

This topic has come up several times in the past few years on this forum. I have previously expressed my opinion that design of a bridge is considerably more difficult than residential framing, because of moving loads, force of water, need for guardrail, and difficult to understand code and legal issues. Some on this forum felt that a small bridge over a small creek was no big deal, didn't really need a design, and could be built using large wooden elements such as telephone poles, pre-engineered trusses, aluminum I beams, steel ibeams etc.

As a professional engineer, I would NEVER offer advice on how to design or build a bridge unless I had a contract to do so. The reason is very simple, if I give you advice on how to design it or build it, and you take that advice and actually go ahead, then something goes wrong, I have a serious problem with my license and career. I expect that any other professional engineer on this forum feels exactly the same way.

Therefore, you should expect to get suggestions solely from non-professionals, who believe that they are insulated from any liability regardless of how badly the results turn out. Some of these folks are probably very knowledgeable, and will offer sound, workable suggestions. Some of them may know absolutely nothing about bridge building, moving loads, and water forces. How are you going to tell the difference? And which advice are you going to rely on?

My suggestion is to go to your local building inspector, tell them what you want to do, and see if they can point you in a good direction. There are companies which manufacture pre-engineered bridges, that could be a starting point. You are probably going to need a permit, maybe more than one, and the authorities with jurisdiction no doubt have requirements about clearance, anchorage, and materials. You ultimately may need to hire an engineer that actually knows something about bridge building, licensed in your jurisdiction. This is not the end of the world, engineers actually sometimes perform a useful service, and designing your bridge could be one of them.


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## Joe Carola (Apr 14, 2006)

Daniel Holzman said:


> This topic has come up several times in the past few years on this forum. I have previously expressed my opinion that design of a bridge is considerably more difficult than residential framing, because of moving loads, force of water, need for guardrail, and difficult to understand code and legal issues. Some on this forum felt that a small bridge over a small creek was no big deal, didn't really need a design, and could be built using large wooden elements such as telephone poles, pre-engineered trusses, aluminum I beams, steel ibeams etc.
> 
> As a professional engineer, I would NEVER offer advice on how to design or build a bridge unless I had a contract to do so. The reason is very simple, if I give you advice on how to design it or build it, and you take that advice and actually go ahead, then something goes wrong, I have a serious problem with my license and career. I expect that any other professional engineer on this forum feels exactly the same way.
> 
> ...


Good post. Just hope that people listen. Just because this is a DIY'er site...people think that they can do anything themselves without any professional advice...when what they want to do should be designed/done by a professional.

*Not every project is for a DIY'er!*


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## Clutchcargo (Mar 31, 2007)

I would consider a suspension bridge. Back when I was a yout, we built one in YMCA camp. It was awesome. It took a crew of misfit pre-pubescent kids, but we did it. Of course, back then we weren't as lawsuit happy as we are today.


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## Tizzer (Jul 24, 2010)

Have you considered acquiring a couple beavers to dam up the creek?


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## 1910NE (Sep 5, 2010)

If the creek is small enough, and you can do so legally, why not drop a culvert in and then build a path over it?


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## Vedder316 (Oct 1, 2011)

Well I have decided that the 2x12x16's are definitely not going to work. That you all for your input. Any idea on what I can use to span the 25 feet? There in no chance of water hitting. I am contemplating the utility poles idea but am unable to find any.


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## Aggie67 (Dec 20, 2008)

What's the aversion to doing it correctly, and calling an engineer?


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## Vedder316 (Oct 1, 2011)

Aggie67 said:


> What's the aversion to doing it correctly, and calling an engineer?


No aversion at all. I have little experience and thought I would be able to do it correctly. Hence coming here and asking. Also I cannot afford to hire a contractor to design and build it. If I can find some thing to safely support the weight such as utility poles I see no problem in doing it my self.


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## BigJim (Sep 2, 2008)

The utility company use to sell used phone poles. I am not saying anything against engineers at all, they do know what they are talking about. I have seen bridges built of phone poles that held a mid size farm tractor with implements attached. Three poles will surely hold a lawnmower and a man in 25 feet.

You may be able to find a salvage yard that sells railroad trussel timbers I have used them before also and if it will hold a train...


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## havalife (Mar 23, 2011)

All I will say is Good luck, btw before you hire an engineer you may want to meet with the ACOE www.usace.army.mil, that will cost time and money but after you talk with them you will most likely decide to forget the bridge thought. If they do not stop you EPA will.


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## Willie T (Jan 29, 2009)

Well, I do have to say that long before anyone even knew how to spell the word engineer, our ancestors simply felled a big tree at the river's edge, and then walked across it for years and years.

I applaud your pioneering spirit.


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## Oh-Fudge (Sep 1, 2011)

Cool idea Vedder. I could see myself motoring on my Craftsman over a little bridge to the back 40 :yes:.

Why DIY? Why do we all DIY = $$$$$. Professional Engineer = $$$$$.

To the engineer guys, amen, great advice and totally right on. But, I'll bet you don't (and shouldn't) give blueprints away for free. Hey, if I had money out the wazoo I'd hire a horticulturist to mow my grass.

Pictures of this "creek" would be great. If this guy lives on a 100 acre ranch in Montana and this little creek is totally on his property and he wants to make a little homemade bridge and he is the only one who is going to plunge to his death then why can't he give it a try? DIY-at your own risk. But, Dude, if we're talking about a 40' "ravine of death" here, and you were serious about butt joining 2x16's to span 25', then I have to agree with the engineer guys :no:.


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## AGWhitehouse (Jul 1, 2011)

Utility Poles are a great idea. But if you can't find them, you might try a "truss type" bridge. Here's an idea of what I mean: http://mathemati.ca/images/Model_B3.gif

Think of it like building a roof on a house. You have the rafters and they are held together by collar ties.


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## Msradell (Sep 1, 2011)

AGWhitehouse said:


> Utility Poles are a great idea. But if you can't find them, you might try a "truss type" bridge. Here's an idea of what I mean: http://mathemati.ca/images/Model_B3.gif
> 
> Think of it like building a roof on a house. You have the rafters and they are held together by collar ties.


What is that bridge for? Considering it's only about 12" long it sure isn't for much.


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## oh'mike (Sep 18, 2009)

Crossing a brook on his riding lawn mower,If I read it correctly.


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## Oh-Fudge (Sep 1, 2011)

*Need to build a 25' flat bridge*



Msradell said:


> What is that bridge for? Considering it's only about 12" long it sure isn't for much.


Uhmmm, it says in the title that it's a "25' " bridge? :wacko:


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## Blondesense (Sep 23, 2008)

Who's on first?

The OP wants to build a 25' bridge. The example bridge in post #21 is only 328mm.


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## WillK (Aug 29, 2010)

I think we've got a base assumption that this bridge necessarily has to go 25' unsupported except at both ends. You're only looking to run a riding lawnmower across it. Is a mid-span support out of the question? Seems it would simplify the issue considerably.


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## AGWhitehouse (Jul 1, 2011)

Msradell said:


> What is that bridge for? Considering it's only about 12" long it sure isn't for much.


It's a random internet image that generally displays the idea of truss bridge. I thought it was obvious that it wasn't a plan for the OP's case, but I guess I thought wrong.


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