Posted by Jeremy French on October 23, 2015
At some point, imagination has to meet reality. Teleportation is awesome, but it is still not real. Having a table with a double cantilever of this scale is certainly not in the realm of teleportation, but if some serious consideration is not taken, the results will be the same- body parts scattered about.
My highly sophisticated method of engineering has a pretty good track record. "Uhhh, that looks good, add some more." That said, this is a project worthy of calling in someone who is handy with a Ti85 and has letters behind his name.
: Enter stage right- Jeff Girard of CCI ::
We have a good article for understanding the basic principles of reinforcement, which is worth a read if you are not familiar. This article covers the basics, but is not sufficient when the possibility of catastrophic failure is present. When something has the potential to cause serious damage, that's when you better call someone who knows how to consult the books. Thankfully Jeff Girard was willing to oblige, thanks Jeff!
Following a thorough analysis, an ample amount of coffee, and some sophisticated looking spectacles, what we found goes counter to some of the basic principles of reinforcement. The finished table was to measure 4" thick, and once you figure in for the thickness of the rebar needed, and the amount of cover from the elements the steel would need, we ended up with rebar smack dab in the middle of the countertop!
All in all, we ended up with a big footer, and lots of steel.
A few notes ::
We ended up bringing the rebar up closer to the surface than what we originally planned. Since the concrete was densified through modifications we made to the mix design, we didn't need a traditional amount of 'cover' to keep the steel from the elements. We ended up with 1" of cover from the top of the steel to the surface of the concrete.
Did it work? We can get more into that later in our final analysis. The fact is that the mold was removed less than 24 hours after casting, and no limbs were lost in the process. Good sign!
Thanks to Steve Millard for the aerial shot here. The drone proved equally useful as a ceiling fan in this heat, heat that proved to be the curveball we would face on casting day...