If you read the post “I my own general”, you’ll get the idea. Roger Dodger kept asking me to consult an engineer to calculate where to put internal supports for the roof and etc., since he (and most other people) are new to underground construction. I called and called and explained my project to 14 different structural engineers, and none of them wanted to just do a little calculating for me; they wanted to charge me thousands of dollars to come up with a blue print. Which, of course, would be useless once the digging unearthed a pluto-sized boulder or an underground river, so I didn’t want to go that way, and just waited for the Universe to point the way. Which she has.
Yesterday Roger Dodger came over and really applied his brain to the issue, and came up with a reasonable fascimile of a plan, but he needed some numbers to be sure that the roof wouldn’t collapse, so my morning at the PO today was dedicated to research. Now I’m so familiar with board feet (a 10 X10 inch post, 10 feet long has 83.3 board feet…just in case you, like me, were wondering), snow loads, the weight of dirt, and the unit stress for bending in pounds per square inch of doug fir its positively scary.
Here’s what I know:
1) Earth roof, saturated; 6″ @10 lbs/sq.in = 60 lbs/sq ft
2)crushed stone drainage layer; 2″@ 10lbs/sq.in = 20 lbs/sf
3) snow load at 5830 feet elevation, 46.93 deg lat, 110.74 deg long (that’s pretty darn close to my location)=78 lbs/sf
4)Structural load; typical for scale of heavy timber structure, includes timber, planking, membrane and insulation; 15lbs/sf
5)Total maximum load = 173 pounds per square foot.
AND I now know that the unit stress for bending in common structural doug fir is 1450 pounds per square inch, and the unit stress for shear is 95.
Aren’t you glad you now know this too?
Love and quadratic equations,