Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
(OP)
We typically use 12 x 12" oak timbers as cribbing for heavy equipment maintenance. Typical point load weights = 20,000 lbs . Would like to use aluminum tube instead of the oak due to fire code/ fire loading issues.
Assuming 6" x 4" tube, trying to determine thickness required to support 20,000 lbs point load . Assuming 6" flat on floor, I would treat each 4" vertical leg as a column. Assuming 1/2" wall thickness, compressive stress = 20000/(0.5 x 4") = 10000 psi << 0.6Fy = 0.6 (21000) = 12,600 for T6061 T6 aluminum ... OK ... Agree with this logic ??? Thanks..
Assuming 6" x 4" tube, trying to determine thickness required to support 20,000 lbs point load . Assuming 6" flat on floor, I would treat each 4" vertical leg as a column. Assuming 1/2" wall thickness, compressive stress = 20000/(0.5 x 4") = 10000 psi << 0.6Fy = 0.6 (21000) = 12,600 for T6061 T6 aluminum ... OK ... Agree with this logic ??? Thanks..






RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
What sort of point load is it?
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
I'd be hesitant to use tubing of any material as cribbing, because there's always some point load that can buckle the walls.
I would prefer oak to aluminum for cribbing, because in a fire, charred oak will be there long after the aluminum has softened, buckled, then melted and pooled. Take a long look at the mechanical properties for aluminum at even slightly elevated temperatures.
You should also talk to your insurance company; they may have some input.
Mike Halloran
Pembroke Pines, FL, USA
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
You haven't defined what a "point" load is, typically has to be over some finite area.
A tube could conceivably flatten to one side at lower loads than what column failure would indicate, depending on the lateral load applied.
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
Further, the stiffnesses of the two comparatives are nowhere near equivalent. The oak wins.
RE: Use of 6" x 4" x ?" Aluminum tube for heavy equipment cribbing
A slight irregularity on the piece, the floor, the rigging, or the machine forging doesn't distort, scar or damage the (very expensive) part you are supporting. The wood compresses and accepts the change "gracefully". Also, a 12 x 12 or 16 x 16 timiber is very stable against tipping over if bumped or jarred while rigging, or if the load does not land exactly evenly when coming down.
12 x 12 (or 16 x 16) is NOT fireproof per se, but will not burn under any normal circumstance or normal ignition sources. Forest fires, for example, burn right past this kind tree trunk, leaving them only marked on the outside bark. (Then again, when has somebody citing cribbing as a "fire danger" been considering time-until-ignition?)