Cribbing capacity

What are your thoughts on cribbing capacities, and stacking heights? Where did you derive your information? Too many folks preach "crib as you lift", however rescuers aren't told all they need to know. Let's hear it. What are your SOG (P)s for figuring capacity?

As a general rule of thumb, the capacity of each "pillar" of a box crib is around 6000 lb. This would give a 2x2 box crib with 4x4 lumber a capacity of about 24000 lb. Go up to 3x3 crib with 4x4 lumber, and you now get a capacity of 54000lb. A soiid box crib of 4x4 lumber would have a capacity of 150,000lb. If you jump up to 6x6 lumber, the numbers rise. You also need to be able to estimate the weight of the object you are lifting. Cars and most trucks are not going to cause catastrophic failures. On trucks, remember that by law the gvw must be posted, and many larger ones are 80,000 gvw's. Worst case is to plan on the max weight. For collapse situations, figure that 1 cubic foot of 4000psi concrete debris is approx 120lb. one cubic foot of light frame debris is generally 25-50lb, this is variable dependant on other factors such as furniture,equipment load on the floors..etc.
Height capacity should be no more than 3 times the width, so if you have 24" long 4x4, the stack height should be no more than 6 feet...the higher the need...the longer the lumber needs to be. If the crib is to be used as a lifting platform for an air bag, the top layer should be solid, and generally would not want to build any less than a 3x3 box crib (out of 4x4 lumber).

[This message has been edited by e33 (edited April 09, 1999).]

Is that hardwood or softwood?

Cribbing should be out of hard woods like oak, preferebly rough cut. No stains or paints of any kinds should be added due to they hide damage. Also vehicle fluids on a painted surface can be slippery. Add a handle for convenience made of webbing and your set.

Softwood..and cribbing of softwood lends itself better to cribbing as if it begins to fail, it creaks and cracks. It really boils down to personal preferance...and there is also a big weight factor difference.

I agree with e33,cribbing should be cut from soft woods.They will "tell you" when they are reaching failure point..Also thats why you're crib members should overlap each other at least the thickness of the lumber so you can see the ends starting to split...