Starting my bridge!!

[scootr]

The mix will have to be real wet for a chute. You may have to push it down the chute otherwise.
hugs, Brandi

Use a vibrator Long chutes are a drag

 

[Doorman63]

Use a vibrator Long chutes are a drag

That’s concrete humor?

I actually have 40’ (4-10’ pieces) of U shaped 22 or 24 gauge sheet metal shrouds for some coiling doors.

 

[EddieWalker]

Interesting build. What type of vehicle are you planning on driving across your bridge?

 

[Doorman63]

Interesting build. What type of vehicle are you planning on driving across your bridge?

Shooting for my Kubota L2501 and/or our 2007 F150 farm truck
Pick up is about 6k

 

[LD1]

Without knowing the wall thickness of the tube.....off the cuff....I'd say the max for that structure is about 2500# presently. Based on the fact that you are spanning a little shy of 20' and deflecting ~1/4" with ~1200# of ATV's.

There is FAR more that goes into engineering calculations.....but for anything but the shortest of spans (where stress/shear become a factor).....L/360 deflection is usually a pretty good rule to follow. That is the length in inches divided by 360.

So say your span is ~18'....thats 216".......and 216/360 is 0.600" deflection MAX. And since you are nearly half that with teh ATV's.....safe to say thats about half the max load that structure will handle.

Then of course you have to have sufficient decking to handle the wheel load of 2.5' crossmember spacing.

Also throw in the fact that the entire weight of the truck or tractor are NOT right in the middle at the same time. A full sized pickup has a lengthy wheelbase. But then you also have to account for dynamic load/stresses of the vehicle moving.

I would forget the aircraft cable and truss it with some rebar similar to whats pictured above but on the BOTTOM so it stays in tension. That will add tremendous strength. But dont just weld the ends at a small point where the rebar comes back to the bridge. Flatten it back out so you get a good 4" or so of weld. Some 3/16 x 2" flat would work too.

Whatever modification you make, slowly work the weight of the load up and keep an eye on deflection. Dont go past 5/8" or so

 

[dodge man]

I don’t think a cable under tension is going to add a lot if any strength.

 

[Lineman North Florida]

How about jetting a pole down mid-span of your bridge on each side to support the weight in the center, we used to jet poles down in water all the time and always found that creosote was far superior than any cca pole in water.

 

[Doorman63]

Without knowing the wall thickness of the tube.....off the cuff....I'd say the max for that structure is about 2500# presently. Based on the fact that you are spanning a little shy of 20' and deflecting ~1/4" with ~1200# of ATV's.

There is FAR more that goes into engineering calculations.....but for anything but the shortest of spans (where stress/shear become a factor).....L/360 deflection is usually a pretty good rule to follow. That is the length in inches divided by 360.

So say your span is ~18'....thats 216".......and 216/360 is 0.600" deflection MAX. And since you are nearly half that with teh ATV's.....safe to say thats about half the max load that structure will handle.

Then of course you have to have sufficient decking to handle the wheel load of 2.5' crossmember spacing.

Also throw in the fact that the entire weight of the truck or tractor are NOT right in the middle at the same time. A full sized pickup has a lengthy wheelbase. But then you also have to account for dynamic load/stresses of the vehicle moving.

I would forget the aircraft cable and truss it with some rebar similar to whats pictured above but on the BOTTOM so it stays in tension. That will add tremendous strength. But dont just weld the ends at a small point where the rebar comes back to the bridge. Flatten it back out so you get a good 4" or so of weld. Some 3/16 x 2" flat would work too.

Whatever modification you make, slowly work the weight of the load up and keep an eye on deflection. Dont go past 5/8" or so

This is why we love this place!!

I have multiple 50’ lengths of 3/8 crane cable (not aircraft cable). 5k capacity turnbuckles aren’t hard to get…..that’s where my cable idea came from.

The rebar/flat stock idea work for me as well……overhead welding isn’t my strong suit so that’s why I was shying away from welding under the bridge.


The decking….I was gonna build a couple different test fixtures to see what will hold the tractor/pick-up.

I was thinking of just throwing some c-channel/tube steel down where the wheels ride and wood plank the rest……this idea has me nervous if someone didn’t drive on the steel.

 

[Doorman63]

I don’t think a cable under tension is going to add a lot if any strength.

A cable under tension bowed down (4 or 6”) in the center should?

 

[Doorman63]

How about jetting a pole down mid-span of your bridge on each side to support the weight in the center, we used to jet poles down in water all the time and always found that creosote was far superior than any cca pole in water.

This is my last resort. I have another bridge with poles/cross bracing/etc in the center. I’m trying to see if it’s possible not to use them.

 

[LD1]

If overhead welding is what you want to avoid, you could use a 3" wide strap that's wider than the 2x6 then it's not an overhead weld....only the 6" or so stand-off in the middle is. Which that weld to the bottom of the tube would be under compression and not nearly as critical.

Or if using rebar....you could always weld the rebar to a 3" wide by 4" long piece of flat stock. Then weld the flat pad to the 2x6.

If you yousef the cable....how would you attach the turnbuckles? As thin as the tubing is.....I would trust the tension with a bolt to anchor the cable. The idea of the rebar or strap is distributing the force over a larger area.

But if your gonna guard-rail it anyway....you can truss the top like an iron bridge or sides of a landscape trailer as mentioned.

Lots of ways to make it stronger....but without knowing a budget....or what scraps you have on hand....hard to say what will work best for you.

 

[LD1]

This is my last resort. I have another bridge with poles/cross bracing/etc in the center. I’m trying to see if it’s possible not to use them.

It's certainly possible....if you want no poles.

Even just welding a 1/4"x4" strap top and bottom direct to the 2x6 (basically making an I-beam but with the tube for the web)....you would nearly quadruple the strength.

I really wish I had seen this post before you had the bridge in place and I would have advised you before you set the beams

 

[Doorman63]

It's certainly possible....if you want no poles.

Even just welding a 1/4"x4" strap top and bottom direct to the 2x6 (basically making an I-beam but with the tube for the web)....you would nearly quadruple the strength.

I really wish I had seen this post before you had the bridge in place and I would have advised you before you set the beams

Re:cables
Flat stock “sandwiching” the tube
1/2 or 5/8” bolts with spacers top and bottom
Bottom bolt would have cable looped thru……no welding on ends.
Center spacer is cut from a 4x4x1/4” tube approx 3” long….allowing a good weld from above on both sides.




Flat stock I can get. I could do the same set up so no overhead welding.

Trying to keep my budget low……under $1000 including concrete.
So far I’m at $180 for the Timbers. Steel is free!

 

[Mark_G]

This is a curiosity question, could a utility trailer or decked trailer for hauling vehicles be used as a bridge? Take the wheels etc. off and rest on supports on each side? Seems like an easy bridge idea for relatively short spans.

 

[LD1]

This is a curiosity question, could a utility trailer or decked trailer for hauling vehicles be used as a bridge? Take the wheels etc. off and rest on supports on each side? Seems like an easy bridge idea for relatively short spans.

Yes it can. And alot of people use a trailer for building bridges

 

[rich1023]

If you subscribe to "mother nature's journal", you will be able to exact the positioning of your bridge over troubled waters. Erosion has a way of surprising us, determining which bank might fade and which might feed is a 50/50 science at best. My $.02 would offset center to the downslope side, also influenced by the bank trend in your photo. Rickrack could help save erosion if you have access. Good luck on your project, stay safe!

 

[1700E Dreamer]

Looks good

 

[WoodChuckDad]

I wonder how much the steel would have cost. Till you said it was free, I was wondering why you went that way. Looking forward to seeing how you do this.

 

[Doorman63]

Thanks for all the well wishes everyone.

No progress since a couple weekends ago. The bridge isn’t at our full time residence.

We are going this weekend.
I’ll (hopefully) be making some mock-ups for the bridge decking and driving one wheel of the tractor and pick up on them to see how the wood responds.

I’ll build a small tube steel frame with the correct spacing and lay it on the ground. If the mock-up fails……nothing gets broke or wet!

 

[51allis]

It's certainly possible....if you want no poles.

Even just welding a 1/4"x4" strap top and bottom direct to the 2x6 (basically making an I-beam but with the tube for the web)....you would nearly quadruple the strength.

I really wish I had seen this post before you had the bridge in place and I would have advised you before you set the beams

Been following this build as I have a very similar landscape on the back of 20A and eventually want to build a bridge that would hold about 7000#. If anything my creek might be like a 2ft wider (longer span for the bridge). You had mentioned "I" beam...I have an old 14'x70' mobile home that is basically garbage except for the steel I beams under it (its an old one with the 1-1/2" outside walls). Those I beams are about 12" to 14" high and the steel in them is 5/16". Could I repurpose those I beams to build a similar bridge that would hold the weight I need?