Building a bridge over a creek (driveway)

[Softcoin]

I bought a piece of property that has a creek in the front of the property.
There is a wood bridge there now, (20 years old) 7 sets of 5 2"x8"x15' boards bolted together w/ cross boards on top connecting them all and runners on top to drive on.
There is a concrete pad on each side of the creek 2ft thick x 12ft wide x 6' deep.

I'd like to replace the wood with 8" or 10" i-beams (as many as it takes) and connect them all with cross boards and runners.

I-beams would be 15' long sitting on the existing concrete pads, concrete pads are 13' apart. so the i-beams would be sitting 1ft of pad on each side. see attached

Does anyone know if this would be strong enough for a single axle dump truck full of gravel?

 

[RedNeckRacin]

a fully loaded tri axle dump truck at 72,380lbs? You better get a Professional Engineer to design this and seal it. There is a big difference between a W8x15 and a W8x67 or a W10x19 to a W10x112.

 

[bigdeano]

There are online calculators for beam strength which would be a good start for you.

 

[Reb954]

This chart should help you figure out what you need.

Keep in mind, the shown ratings are per beam. Multiple beams should be cross braced so they can't roll under a load.

The bigger question is what are you using for decking. The wood decked bridges I have set all use 3" thick plank layed cross wises to the beams, then 3" runners on top of that. But, most bridges I have set use the corrugated steel decking, then get gravel or asphalt on top. For your purposes the wood deck would do fine.

 

[crazyal]

Call up a couple local steel yards and tell them what span you are trying to cross. Sometimes they end up with short sections that they will sell for a much better price than if you specify what you want. Often they can even tell you how much they will support (it'll be not as detailed as what an engineer can tell you). From there you can decide if it'll work for what you want to do.

About 20 years ago I helped my step brother build a bridge for his driveway. He got 7 19' I-beams (forget what size) and we painted then spaced them out. He had a welder come up and put in cross pieces after we got them in place. We then laid down pressure treated 2x4 bolted together with threaded rods. The data he got was from the steel company and the bridge has handled everything from tri axle dump trucks fully loaded with gravel and cement trucks to build his house.

 

[Stimw]

Years ago I drove a single axle dump truck hauling pool sand.
The pit ALWAYS scooped from the bottom of the pile getting the wettest/heaviest sand!!
My worst load was 33,000 lbs gross weight and it was heavy.
This should give you a maximum number to work with.

 

[ArlyA]

The last bridge we did decking was unplanned treated red pine 4x8's. It was designed so a pickup truck could use it. I beam spacing was 3ft centers (as I recall anyway). What about a fire truck?.

 

[Groo]

an I beam sitting between the tires wont do squat unless the decking is pretty stout.

a single axle can be rated for over 30,000 lbs on its own (think I saw as heavy as 38,000lbs for a Freightliner SD single drive axle), so an overloaded single axle might be over 20 tons. a standard heavy single axle rating is 20,000 lbs.

 

[BrokenTrack]

The loads on this bridge would actually be pretty small just because the length is so short. While it is true a triaxle truck or fire engine might roll across it, bridge calculations are done on length and weight. In this case, even if a tri-axle truck did roll across the bridge, because the bridge is only 13 feet long, that means the entire weight of the truck is never fully on the bridge. (The front axle is on the bridge, or the rear axles are on the bridge, but never the full weight of the truck.

It still leaves the three rear axles over the bridge granted, but then that load is spread over 12 tires.

The best way to deal with that is, to put down (4) I beams at truck width, angle irons welded x fashion between them so they do not twist under load, then plank the bridge over with 3x8 planking. I would add bumpers on the outside, or railings depending on height. (Just to limit the liability of kids or grand kids falling off if it is high).


I would not over-think this too much.

 

[Jstpssng]

Sometimes you can also find used bridge steel for sale.