how to calculate max load

[minimustangs]

Hi. New here, not an engineneer by and stretch. I am tool friendly, but no expert.

I have 2 distinctly different projects that require figuring out maximum support loads.

1st Project is a portable 8' x 8' x 12"H riser for a drum kit. I'm guessing that 500lbs would be the max load here. The catch is keeping it lightweight and strong while being solid enough to have next to no "spring".

2nd project is a spring/summer ongoing thing. I need to bridge a creek on my property. I want to be able to span about 20 feet, and carry a loaded ATV & trailer, with the trailer loaded down with chopped hardwood. I'm guessing this is going to be a load in the range of 2000 lbs.

Really all I'm looking for is a web link to information on dimensional lumber and how far I can span. If you happen to have more that would be great.

My wife has told me that she knows from previous projects I've built there will be no problem with me building it strong...because I tend to overbuild everything. What she put to me was "Does it really need to be THAT heavy duty"? If I don't need to use 2 x 12's why should I incurr the extra expense. On the other hand if I miss the mark and don't build it sturdy enough, at the least i'll have to rebuild it - after getting quite wet...

Oh yeah, on other consideration....

During winter the bridge will likely get covered in snow - up to 3 feet, maybe 4.
During the winter I'll need to access this same bridge with a skidoo and trailer. This time though the trailer will be hauling 55 gallon drums of sap.

Thanks for your input.

Steve,

Huntsville, Ontario

[giddonah]

light weight and strong, go with welded tube frame. you can design it to bolt together so it can pack up. Deck it with plywood.

For the bridge, seriously, get an engineer.

[Don_P]

I agree on the engineer part, remember when you get into rolling loads, like the bridge, it is a good idea to double the load, triple it if you plan on hitting the brakes, dynamic loads can get big fast.

This calculator is on the AFPA website;
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

I've put together some calcs to model with before I call in the expensive guys.
http://www.ls.net/~windyhill/Calcs/beamindex.html

Hope this helps

[minimustangs]

I agree with the hire a pro sentiments you have both mentioned. I actually have purchased plans for a bridge, I mostly was asking for personal interest & so that I could apply those values against the plans I have. These calculators seem to answer that question pretty well.

Thanks!

Steve,
Huntsville, Ontario
http://ca.geocities.com/straightupontheweb