Time for a new bridge - how to engineer?

[paulharvey]

You asked about a bridge, so maybe you Want a bridge. I Google "agricultural bridge designs" and the first article is PDF from Alabama with a lot of food info. Little technical, but recommends 3" wood decking, 8"-10" wide. Gives some specs on steel W-beams, ect. No idea how to link a PDF.... many of the state agricultural schools have designs for barns ect free online to view

 

[Sodo]

Maybe it just needs a little help during the time the trucks are delivering gravel. Can you support the bridge at center with a stack of wood scrap lumber in the streambed (and let the stream just leak thru the wood). The remove it after your gravel is delivered? Maybe can set a steel pipe in with the wood stack to let the water pass easier.

It would be useful to know what size truck and if they are tandem or single axle.

Culverts make a creek look like a ditch. A bridge has more charm. But maybe it is a ditch.

 

[Egon]

If the bridge think about beams that are much deeper than wide. They can also be laminated. For supporting heavier vehicles it might be best to get a standard plan to follow.

 

[vtsnowedin]

Well if you want a quick short bridge consider a flatbed trailer with the wheels cut off.

 

[Catch95]

If you search under my name you can see the posts I did on building a new bridge on my property -twice! First time to replace one and the second time after an old footing I used gave way during a flood. I then moved the bridge to a new location using a crane.

The bridge has worked really well. Couple of things I learnt (without going into the engineering of beam and decking sizes etc)

Footings are very important! Think twice before using an existing one. Turned into an expensive mistake for me.
Make sure you anchor your beams to the footings. Water can exert tremendous force even in a small stream when flooding.
Be careful about where you place the footings. Ensure they are far enough back from the stream to prevent erosion under them. I stabilised my banks with a couple of rolls of chain link fence material pegged down and gabion baskets.
Ensure your beams are at the track width of the heaviest vehicles likely to use the bridge. I set mine for my tractor.
Put a rail on the edges for those times your neighbours are leaving late at night after a few beers....
Allow enough gap between the decking boards for expansion. Surprising amount.
Don't underestimate how much fill you will need to bring your track up to the level of the bridge. Have a look at the pics from my post re moving the bridge. Took many truckloads of road base to get up to the bridge deck height.

I really enjoyed doing my bridge even though it was a back breaking exercise. Still get a quiet sense of pride each time I drive over it.

Good luck

Mark

 

[KennyG]

You might want to look at my bridge thread

http://www.tractorbynet.com/forums/projects/289644-my-bridge.html?highlight=bridge

Look at how I did the footings. Your bridge can be very short but I think you want good footings. Mine has a span of about 12 feet and the calculated capacity (with safety margin) is about 5 tons.

 

[vince2]

My experience with building several bridges was that no commercial trucker would take the risk of crossing a wooden bridge, no matter what the tables say. I had to build a ford, a crossing from heavy rock, so they could bypass the bridge, of course only passable when the water is low, but they rather go through some water on solid soil then run any risk with an unknown bridge. If I had known that in advance, my bridge would have been more modest in capacity for cars, PU trucks and tractors and saved me a lot of worry.

 

[buckeyefarmer]

If you want a gravel truck to drive over, a culvert is the answer.

 

[newbury]

Have you read http://armypubs.army.mil/eng/DR_pubs/dr_a/pdf/tm5_600.pdf?
Bridge Inspection, Maintenance and Repair

 

[JeremyL]

While the preponderance of the recommendations are for a culvert, my wife really likes the bridge option since that it what has always been there (since her grandparents' day). Local lumber yard has #1 used railroad ties, 7" X 9" X 8'. If I use them as beams, I shouldn't have to worry about rotting, and can afford as many as it would take to make the deck sturdy. One possibility would be to use 4" X 6" X 10' posts for the decking.

Anyone know how I can calculate how many beams I need to carry the load of a small, loaded gravel truck?

Thanks for all the information!