Building a bridge in a flood plain?

[paintman161]

I wish i could do something like this! Nice bridge!

 

[Depmandog]

My work takes me around the demolition business and have spent considerable time at yards of demo contractors. You would be amazed at what steel components come off demolition projects.

Bar joists are one of those construction materials that are ideal light gauge bridge building products that can be bought pretty reasonable in price. In your case, a 5-6' wide bridge you would want three joists.

The neat thing about bar joists, the load span data has already been performed (assuming you can identify the type). From a quick check on a 40' bar joist - it appears a 24" or greater depth give you adequate support for a light deck bridge. (Of course you will have to weld block bracing to your bar joists to tie them together).

You could pour a concrete stem wall on each end, say 6' above ground. Allowing for 2' of bar joist, this would give you 4' of clearance above the bank-full water level, allowing for flood conditions. You could do the same thing with railroad ties..but that would be more work IMHO.

Then build a wooden ramp up to the bridge on each end (or ramp up with dirt). The floods would probably take away your approach ramps, but the bridge would be safe unless it was a massive flood.

Use pressure treated lumber as bridge decking, some cable as bridge rails.

Bar joists around here will run .50 a pound. These joist are going to weigh around 400# each.

 

[cbarlandandcattleco]

Go to your county FloodPlain Manager and he should give you the information you need. If not go to fema and search for floodplain proof bridges. it is available. I am retired as an FEMA FloodPlain Manager. If I can be of any help. let me know. Bottom line, The bridge needs to be above the Base Flood Level in that area. Ron

 

[Tractor Seabee]

I want to build a bridge over a creek, it is about 40'-0" from edge to edge. Most of the year the creek is below the surrounding banks. But once maybe twice a year (depends on how much rain or snow melt) it does flood the surrounding areas but goes down within 2 days. I would like to make it 5' wide to drive an ATV across.

Is there any way to do this without having the bridge float away when the water floods the area?

thanks!

I read through the posts on this and did not see any real answers to the questions folks asked in trying to help you. It is hard to visualize your problem. There are a lot on innovative guys on there with a lot of varied experience. I have built expeditionary bridges out of many things but never quite as long as you indicate. I have been in heavy construction all my life (50+ years).

Important Questions:
-what is the normal water level (distance below the top of bank to water
-how high over top of bank bank does the water get in flood stage
-how fast does the water flow during flooding
-at flood stage how far out does the water spread from the 40' you are planning on the bridge to be
-what is your budget
-can you get a concrete truck to both banks
-if not, can you mix concrete on both sides
-are there trees on both sides that will support rigging tackle to drag the bridge across with
-can you get pickup truck or tractor to both side
-can you get a semi truck to one side
-what equipment do you have, can borrow, rent, or need to buy

First thing you have to do is plan. A project like this you cannot start and let it grow as you go.

A 40' span was mentioned but that may be cutting it too close to get a good head wall installed on each end.

My thought is a 53' semi flat bed trailer from a truck wrecking yard. You should be able to get one for a little more than the scrap value as they do not have to cut it up. You want one rear axle left on for over the road transport. Get it to one side and park at right angle to the creek. Lift the 5th wheel end and cut away the 5th wheel and landing gear to leave smooth rails Rig a haul line, preferably with a winch anchored 5-6' above the ground if possible. Drag that end over the creek and center the length. Drop the haul end for now. Lift the rear end and cut away the spring hangers to leave smooth rails on that end too.

Now you are ready to do the head walls. (If you can plan and layout well you can do this ahead of moving the trailer over the creek.) This is where site conditions dictate method so you will need some local advice on how deep and wide. You want at least 2 yds of concrete on each end more if you need to get deep to get bearing (that is a good reason to go 53'0 to get away from the creek mud). Make them 2' longer that the bridge deck is wide and 18" wide. The higher you put the tops above the ground the harder it will to place the deck on it. I would make close to ground level if you don't need more elevation to clear fast moving creek water. Saves forming above ground also. After curing gradually lift and move the deck over the head walls a little each side at a time till in place. If you can afford a crane now is a good time to do that instead. There are many ways to get the deck in place including doing the head walls first and setting as part of the move across the creek initially.

You will have to fill in all the little details this book does not have space to do. That is why this is not a project for a novice with no construction experience.

Keep us all posted as you go along with lots of pictures.

Ron

 

[Shield Arc]

I use to build bridges for a living, this is where you start!

 

[Shield Arc]

Build a bridge that can float

I've built a couple of those.

 

[MotorSeven]

TS, remember, fast moving flood stage brings lots of interesting things down stream. I have see 25" diameter trees with the root ball attached ripping and rolling along in the current of big floods here. That is why I chose to go 5' above the deck, which is 4' above the high water mark...still it might not be enough to keep something like that from snagging the span and pulling it along with it. A lightweight bridge here with a minimum clearance to the high water would not last one season.

Here is a video of a moderate flood last winter. This is the County concrete bridge downstream 1/2 mile from the bridge I built:
[video]http://s271.photobucket.com/user/motorseven/media/Farm/Jan2013Flood_zpsf93fe375.mp4.html[/video]

 

[MotorSeven]

And here is a still shot:

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[Kapnfriday]

MotorSeven - I like your bridge. How did you get it across the creek initially? Did you do something like Tractor Seabee described and winch it across with your winch anchored to a stout tree on the far side? Did you have to flip the bridge to an upright position, or did you get it across in that position?

I'm building a footbridge over a small creek (4-5 feet across) using utility poles as my main supports. I'm trying to figure out how to get the poles all the way across since I can't access the other side with my tractor. Thinking of using chains and a couple come-alongs fixed to a tree.

 

[Tractor Seabee]

MotorSeven - I like your bridge. How did you get it across the creek initially? Did you do something like Tractor Seabee described and winch it across with your winch anchored to a stout tree on the far side? Did you have to flip the bridge to an upright position, or did you get it across in that position?

I'm building a footbridge over a small creek (4-5 feet across) using utility poles as my main supports. I'm trying to figure out how to get the poles all the way across since I can't access the other side with my tractor. Thinking of using chains and a couple come-alongs fixed to a tree.

I recently built a 16' long by 9' wide bridge over my creek. Used 3 RR ties for the stringers. I strapped one end under the FEL Bucket, wedged the end of the tie under the brush guard. When I lifted on it it cantilevered out and I just eased them over from one side. Took a couple tries to get the strap length right but then easy. Only lifted about 1' off the ground as it was feeling a little light in the A end even w/ the BH on. That was with a little BX 25.

Ron