Bridge question

[sarti]

I could not find the other thread on this and not sure I posted in correct place but I have a creek bridge with 16 ft span made from 2 treated 6x6 glued and bolted together Beams spaced same as tractor tires Right now I run my b2630 across it wondering if it would hold a 6000 lb tractor

 

[TnAndy]

One way to find out

 

[KennyG]

No, you are way undersized. Under ideal conditions there is a lot of margin in timber compared to design values, but this one isn't close. Per my copy of Marks Handbook for Mechanical Engineers, a 6 x 6 on a 16 foot span is good for about 1150 lbs uniformly distributed load. The allowable point load is only half that, or 575 lbs. A tractor is something between a distributed and a point load, so I would use the point load value.

As I understand it you have two beams, each is a doubled 6 x 6. I would use an allowable load value of 2300 lbs for that bridge. It's marginal for your B2630 with any attachments.

Your problem is that the bridge beam dimensions are backward. Beams should be as deep and narrow as possible without buckling. A single 2 x 12 has a point capacity of about 750 lbs, more than a 6x6. Therefore, 4 laminated 2 x 12's under each tire track would be about what is required for a 6000 lb tractor. You would need about six 6 x 6's under each track to provide the same capacity.

 

[Henro]

He doesn't say if the 6x6s are glued and bolted vertically or horizontally.

If they are glued on top of each other, with a glue that is waterproof and rated for such an application, then the net result is a nominal 6x12 beam on each side.

If the glue is not effective different story, more like the calculations in the previous post. Sorry can not see that post now to credit the author...

 

[ovrszd]

It was Kenny.

I've got two bridges in my timber.

The first is an ATV bridge that easily handles that task. I made it too narrow for a larger tractor or offroad buggy to get on. Purposely.

The second is wide enough to cross with any vehicle I own. For that reason I made it strong enough to handle any vehicle I own.

Over build once and have a long term bridge. Under build once and have a disaster.

 

[ovrszd]

I'm also anxious to hear clarification of the beam construction. His statement could be taken three different ways that I can think of immediately.

One, not mentioned is the 6x6 being created by gluing and bolting 2x6s together? Thus one 6x6 under each track?

I've never saw two 6x6 beams glued and bolted together to create a 6x12.

 

[KennyG]

I would be very skeptical of the effectiveness of beams laminated on top of each other. With the stress developed by any bending, I think they would delaminate very quickly unless they were factory fabricated under controlled conditions. I assumed they were side by side.

 

[sarti]

I used gorilla glue that cures with moister and used stainless allthread to thru bolt 2 6x6 one on top of the other making a 5 1/2 x 11 1/2 beam. There are two beams total 5 ft apart,,one under each wheel

 

[fried1765]

It was Kenny.

I've got two bridges in my timber.

The first is an ATV bridge that easily handles that task. I made it too narrow for a larger tractor or offroad buggy to get on. Purposely.

The second is wide enough to cross with any vehicle I own. For that reason I made it strong enough to handle any vehicle I own.

Over build once and have a long term bridge. Under build once and have a disaster.



View attachment 637749


View attachment 637750

Assuming that fabrication picture is of the bridge structure assembly shown upside down.
Nicely done!

What about the dog house?
When ya gonna fix that?

 

[KennyG]

I used gorilla glue that cures with moister and used stainless allthread to thru bolt 2 6x6 one on top of the other making a 5 1/2 x 11 1/2 beam. There are two beams total 5 ft apart,,one under each wheel

If you are confident that the glue will hold as well as the wood fibers, you should be OK. I wouldn't have done it that way because I don't have that much confidence in glue.