Need Bridge (deck) input

[dan_m]

Have you considered used railroad ties as decking directly on the I-beams?
I know its a bit lat as you have done your piers already but if the I-beams were spaced at the width of the tractor tires, your decking wouldn't be 'carrying' the load. (Assuming you only plan on driving the tractor across.)

I had not considered railroad ties - that may be the solution.

I set the i-beams at a guesstimated spot based on knowing eventually it'll be more than just the tractor driving on it - I wanted to more evenly support any weight and tire distance. I will be keeping log splitter across creek as well as riding mower, dump carts, and would like to eventually get a side by side to drive around the property and they all won't have the same spacing between tires.

UPDATE: I may even keep my small utility trailer across it (5.5' w x 9'l) - near 600 lbs dry weight and my bx2380 pulls it easily.

I can say for certain, there will not be any automobiles driving on it.

Dan

 

[dan_m]

I would price out white oak and if it isn't too costly throw it down and call it a day. Pressure treated today isn't your fathers pressure treated and it will rot like it was never treated.

Last I looked it was 15-20 board foot - don't recall dimensions but I think 2x8 or 2x10 (real measurements not nominal) so looking at 120-160 per 8' board.

Dan

 

[Flintknapper]

I would price out white oak and if it isn't too costly throw it down and call it a day. Pressure treated today isn't your fathers pressure treated and it will rot like it was never treated.

^^^^^^

Quite true (unfortunately).

 

[Alfred_2345]

I was looking for a simple online beam calculator but didn't find anything specific but you can probably find something that you could use. One thing I noticed is that they talk about "live" load vs "dead" load. The tractor weights you quoted are probably the static (dead) weight. As you are bouncing across the bridge the tractor will be a "live" load and therefore much higher. Don't ask me how much. I'm an electronics engineer not mechanical/structural. Good luck

 

[fried1765]

I was looking for a simple online beam calculator but didn't find anything specific but you can probably find something that you could use. One thing I noticed is that they talk about "live" load vs "dead" load. The tractor weights you quoted are probably the static (dead) weight. As you are bouncing across the bridge the tractor will be a "live" load and therefore much higher. Don't ask me how much. I'm an electronics engineer not mechanical/structural. Good luck

The live load is your tractor.
The dead load is the weight of the bridge structure itself.

 

[dan_m]

I was looking for a simple online beam calculator but didn't find anything specific but you can probably find something that you could use. One thing I noticed is that they talk about "live" load vs "dead" load. The tractor weights you quoted are probably the static (dead) weight. As you are bouncing across the bridge the tractor will be a "live" load and therefore much higher. Don't ask me how much. I'm an electronics engineer not mechanical/structural. Good luck

That was the issue I am running into and looking for any input.

So far the contenders are
1) 2-2x8 or 2-2x10

A double 2×8 or 2- 2×8 header can support 4690 pounds of total weight/ load when spanning to 4 feet, 3130 pounds weight when spanning to 6 feet, 2660 pounds weight when spanning to 8 feet and can support 2130 pounds of total weight when spanning to 10 feet.

A double 2×10 or 2- 2×10 header can support 5000 pounds of total weight/ load when spanning to 4 to 6 feet, 3760 pounds weight when spanning to 8 feet, 3010 pounds weight when spanning to 10 feet and can support 2510 pounds of total weight when spanning to 12 feet.

2) railroad ties

for #1, at any given time, the front or rear wheels of tractor (mower, side by side, etc) will be on 1 cross beam (joist) at a time.

Given that the total weight of anything I am calculating to put on it will be 5,000lbs and a double 2x8 supports 4690lbs then and a double 2x8 should be sufficient as the entire 5,000 lbs won't be on a single cross beam at once - only a portion of it. lets assume bad case of 70/30% weight distribution - 3500lbs on a single cross beam at a given time. for me to exceed the 4690lbs of 2-2x8, 93% of the total weight needs to be on a single cross beam.

Of course, I'll over build and do the 2x8s at shorter spacing and not 12"/16"/24" so that the weight is more distributed over 2 sets of cross beams, not a single cross beam. If 70% (3500 lbs) is in the middle between 2 cross beams, then the forward one will have 50% (1750lbs) of the weight and the rearward one will also be 50% (1750) of the weight.


Dan

 

[Alfred_2345]

The dead load is the weight of the bridge structure itself.

Dead load is any stationary load that does not impart dynamic forces. It can include the structure.

 

[PoTreeBoy]

In the good old days, farmers would cut 4 or 5 big trees across the creek and plank with 2" white oak boards. I've crossed many times with tractor, pickup, hay wagon, etc. They would last 5 years or so if out in the sun to dry.

If you have a source of white oak, you could use that, then treat it like folks on here have treated their trailer decks for additional life.

Or, you may find 'bridge timbers'. Around here they are 3x8x12' pine, pressure treated with the good stuff. My lumber yard ordered them for me, 8' or 16' might be available. They were better quality than the #2 I've recently bought.

Your beams are wider and heavier than what I used, your bridge is shorter and load is lighter, so you shouldn't need much, if any, beam bracing.

Link to my bridge project

 

[dan_m]

In the good old days, farmers would cut 4 or 5 big trees across the creek and plank with 2" white oak boards. I've crossed many times with tractor, pickup, hay wagon, etc. They would last 5 years or so if out in the sun to dry.

If you have a source of white oak, you could use that, then treat it like folks on here have treated their trailer decks for additional life.

Or, you may find 'bridge timbers'. Around here they are 3x8x12' pine, pressure treated with the good stuff. My lumber yard ordered them for me, 8' or 16' might be available. They were better quality than the #2 I've recently bought.

Your beams are wider and heavier than what I used, your bridge is shorter and load is lighter, so you shouldn't need much, if any, beam bracing.

Link to my bridge project

Great work! Awesome bridge.

There are a couple of lumber yards near me and a larger one about an hour north of me in the mountains that might be better suited for having the "bridge timers". I'm sure they have larger beams for the cabins up that way - just if they carry anything like you mentioned.


Dan

 

[lynnmor]

Last I looked it was 15-20 board foot - don't recall dimensions but I think 2x8 or 2x10 (real measurements not nominal) so looking at 120-160 per 8' board.

Dan

I bought two planks of white oak that measured 1-1/2" x 10" x 8' less than two years ago from an Amish sawmill. The price was a fraction of what you were quoted. Perhaps you have other sawmills that will give you an out the door price on the entire order that is more reasonable.

 

[dan_m]

I bought two planks of white oak that measured 1-1/2" x 10" x 8' less than two years ago from an Amish sawmill. The price was a fraction of what you were quoted. Perhaps you have other sawmills that will give you an out the door price on the entire order that is more reasonable.

Those are the ones close to where i live. I haven't checked many and it's been a while.

Dan

 

[North Idaho Wolfman]

Running cross boards is a waste of time and won't do anything for strength.
You don't really need support in the center, but if it makes you feel good put the same blocking in the center as you do the ends.

 

[D2Cat]

Might check with local trucking companies and see it they have any trailers they're selling. Set that trailer bed on your I beams.

 

[Lil Foot]

I was once metal detecting under a bridge very similar to yours, about the same size, and same type I-beams.
They had placed 3 or 4 heavy wall pipes, maybe 4"-5" in diameter, between the I-beams, and drilled holes in the webs for some large threaded rod. They clamped the pipes between the I-beam webs with the threaded rod, and then welded the pipes in place.
The "deck" was rough sawn lumber, (oak?) probably 3"x 10", bolted to the beams with carriage bolts.
Looked like it had been there for 20 or 30 years.

 

[Flintknapper]

Those I-Beams didn't happen to be salvaged from a fire....did they?

 

[dan_m]

Running cross boards is a waste of time and won't do anything for strength.
You don't really need support in the center, but if it makes you feel good put the same blocking in the center as you do the ends.

View attachment 104887

Running cross boards is a waste of time and won't do anything for strength.
You don't really need support in the center, but if it makes you feel good put the same blocking in the center as you do the ends.

Just to be clear I understand what you mean:

Are you saying that "Running cross boards is a waste of time and won't do anything for strength." - you are referring to the cross bracing between the two i-beams? If so, I was only considering doing that in a few spots (maybe 3-4) in case of flooding to help keep them supported and from the left leaning toward the right. So far, one storm did wash a 2x4 I had laying across the top of the footers downstream (this was not long after I completed the footers)- so I know water can hit the bottom of the I-beams.
Also, I'm not sure how the creek will behave in a decent sized hurricane remnant. If I did this toward the top instead of middle of i-beam, I could then add some sort of wood beam between the two i-beams (parallel) to help support the wider gap between the beams. If I go the 2x8 route, then you're correct, there is no need for a "3rd beam".

View attachment 104887

Your top note is what I had in mind, running the 2x8 cross beams perpendicular to the i-beams - with a spacing between them. Then "covering" that gap with top deck running parallel to i-beams.

Interesting point on the middle note, I had not considered not doing a cantilever and bracing the far ends from the bottom of the i-beam. As I pointed out, kind of doing the reverse with longer cross beams to support the handrail to keep it from swaying - The current footbridge that previous owner made doesn't have support and the hand rails wobble like crazy.

I'm not sure on what you're depecting in the bottom - are you showing a side view of the bracing from the bottom of the i-beams to the bottom of the cross braces?

This is why I asked on here, to get some ideas and things I hadn't thought about. I'm digging the idea of bracing the bottom of the far ends from the i-beam.

Dan

 

[dan_m]

Might check with local trucking companies and see it they have any trailers they're selling. Set that trailer bed on your I beams.

I'd have to tear down my fence in at least 2 places to get a trailer that big to the creek. Interesting idea.

Dan

 

[dan_m]

Those I-Beams didn't happen to be salvaged from a fire....did they?

No, they have been sitting outside for a number of years though. They are still solid and no soft spots. The friend I got them from got them from a construction site years ago he worked on - they were just going to bury them. He was going to use them to add another bay on to his shop that he repaired his equipment in (skid steers, mini ex's) now that he's not going to use the beams, he gave them to me. He even used his oxy torch to cut the holes to bolt them to the footers (kept me from drilling them!) and brought them over on a tilt deck trailer. I pulled them off with my tractor, then he set them with his mini ex.

Dan

 

[GSD-Keegan]

very similar in construction to what you have in mind OP.

 

[Russell King]

Here is what I would do.

Get a welder to come out and install the cross members between the beams using square or rectangular tube. Weld these about 4 feet apart down the length of the wide flange beams (what have been called I-beams. These will set the spacing between the beams to be the same for the length of the two beams and keep them from twisting. These will probably be one close to top flange and one close to bottom flange back and forth.

Then you can use these to place vertical legs on and support the length of a four by four running the same direction and length as the beams. attach a four x four on top of both beams so you now have three four x fours the length of the beams. Put two x four (or six or eight) laying flat like deck boards across the four by fours and screw them to the four by fours to create the width of the bridge. Then brace the ends like suggested by NIW above in end view.

in fact that end view is very similar if there was a four by four at the center and on top of the beams.