Another Bridge Thread

[oosik]

Ballegre, After all this professional advice no one will be surprised if you go into the bridge building business.

 

[ballegre]

So I just want to clarify that you are calculating for the 6000lbs per beam and not two single seperate 3000lb loads plus 250lbs evenly distributed for decking.

Well, based on other postings here, I used a tractor weight of 12,000 lbs (2x safety factor) load then I divided by 4 for each wheel. Thus I'm using 3000 lbs load for the calculations.

And I'm calculating for a 12' - 4x12 beam (2 2x12 boards laminated and bolted) to support 3000 lbs.

You saying I need to calculate for the entire 6000 lb load at one point? I'd like to hear different opinions on this if you have one.

Being that your beams are narrow, do the connections (i.e. nails) have any appreciable effect on the top wood fibers being in compression?

I'm concerned the tractor weight would losen the decking eventually so I was planning to bolt the decking to the beams. Should I be concerned about this weakening the beam? Would decking nails be a better choice?

Also, do you have a way to analyze the beams for torsional failure? I think some sort of bracing would be crucial for success in this instance. Some diagonal bracing would be very benefical here. I would consider very stronly going with much more than a 2 or 3x safety factor, 5 sounds much more reasonable. Wood decays outside no matter what.

I was planning on cross bracing, though if I set the beams into the concrete columns at each end I don't think this is necessary.

Using steel plates for your transition areas from wood span to concrete support is an excellent idea and the gluing of members is also an excellent suggestion. Its not worth going cheap. Ove rdesign it in case you neglect something. Just my $.02

I need to look into steel plates. I also read here that I can get steel I-beams from McMaster or other industrial supplier (or use an old trailer frame).

 

[swick1]

You should use entire tractor weight divided by number of beam assemblies, calculate desired deflection, then multiply by factor of safety.