engineering/calculations help

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could i get a little help?  what little i understand about load calculations and deflection, i think i have the right size steel.  here are the details:800lb static load on top of a steel framesteel frame will be 3" x 3" x 3/8" angle36" deep   30" wide    96" highangle on all 4 sides at topangle on 3 sides at bottom  30" width at front on bottom does not have a 3" x 3" in placesorry not good at posting a drawing/plan.thanks. dave.
Reply:Deflection cannot be calculated without more detail as to how the load is transferred to the frame.If you can ensure that the load will transfer to the single angle columns uniformly across the cross section, you will be fine.  However, accidental eccentricity of the load should be considered.  This can be estimated once it is known how the load will be transferred to the frame.The KL/r of the single angle columns is 168 by my calculation.  The limit is 200.  That is cutting it a little close for my design preference.  Using 3" x 3" x 7ga (3/16") square tube gives a KL/r of 85.  That would be what I would use./This advice is given for informational purposes only.
Reply:Post up a drawing of what you're trying to make and also where the load will be applied and I'll look into it for you
Reply:96" tall?  I think that will require cross bracing on the three 'closed' sides.  But, yeah, a sketch will help.  Do you have a pencil, paper and access to a digital camera, or cell phone with a camera?
Reply:the load will be centered on the 36" dimension.  the load is going to rest on the 36" dimension only.  if i change the 3" x 3" angle up rights to 3" x 3" x 3/8" square tube [as fegenbush suggested, although i would rather have 3/8" than 3/16" to attach something to later on] would it still require cross bracing?Dave.
Reply:here's the pics. Attached Images
Reply:You don't mention how tall this 800 lb. static load is, but the bottom is 8' off the ground. If something were to bump it, it will wobble around pretty good. The taller it is, the more leverage it has to work on folding up the legs below it. The cross bracing between the legs is a good idea to give it more stability. At least a 1/8"x1" flat stock run diagonal corner to corner and welded together where they intersect would help greatly. Angle iron or tubing would be even better. Is this going to be anchored to a concrete slab or just free standing? What is the 800 lb. load going to be? Are you sure it's 800, or is it "about 800 lbs." , which could end up being more. How are you going to get this 800 lbs up there after this is built, forklift or something? Will it be up there from now on, till eternity? Will people be around it frequently after it's loaded?
Reply:bistineau,  36" tall.  anchored to concrete floor.   electrical transformer.  yes, 800.  fork lift.  up there till eternity.  people will be around it, but not frequently.Dave.
Reply:Either way you go, angle or tubing for the legs, cross bracing should be considered, to add ridgidity/stability to the structure. A peice of the material that the legs are made from run horizontally about half way up would be better than nothing at all. Especially if you could tie all four legs together at that point.
Reply:Using real rough numbers, 3"x3"x.375" (4) pcs structural steel angle (8.4 square inches), yield strength 36,000 psi, factor of safety of 5, would take a load of about 60,000 pounds. The problem is your primary failure mode is going to be buckling. I don't have my structural book with me but I suspect the .375 angle iron would take the STATIC buckling. Even so, there is no way I would stick 800 pounds up that high without cross bracing. Is there any way to attach the top of the rack to a wall? It wouldn't take much to bump that rack, or have it set in motion by an unexpected earthquake like the Northeast had last year. The buildings were doing a lot of moving and I wouldn't want to see that transformer topple over because a few pieces of steel or a horizontal attachment were missing.Last edited by Fab54; 04-03-2012 at 01:08 PM.Millermatic 211Lincoln Precision TIG 225Century 250 MIGLincoln 225 AC Box (sold)I support my local welding store (Amazon, McMasterCarr, Cyberweld, EBay).
Reply:If you could use square tubing for the legs, vs angle, that would provide much better torsional stiffness in the legs. Which would help resist the whole thing trying to twist or wobble. It would also help if you could use tubing for the top, I suppose, since the overall twisting (if it tried to go sideways) would also involve twisting those top pieces. A closed section (square or round tubing) is much stiffer in twisting than an open section (like angle). Even some gussets at the top, front corners (on the front face, going left/right, not going front/back) would provide a bit of help to resist the front trying to go sideways.
Reply:fab54, the wall behind it is drywall over metal studs, not much meat.redoctobyr, gussets and bracing will be incorporated.  i do not want that thing coming down for any reason other than to be replaced.
Reply:Interestingly enough, HSS 3" x 3" x 3/8" (square tube) is actually a little worse for buckling than the 3/16" thick due to the increased radius of the corners.  However, it would be acceptable.(4) 5/8" anchor bolts (epoxied in) would make sure the bottom doesn't move.  5/8" may seem heavy, but it is the smallest diameter I care to deal with.  96" tall doesn't make me care too much about cross bracing the frame.  It certainly wouldn't hurt to do it.Electrical transformer means it's all dead load, so I think you'll be fine with the suggestions you have.
Reply:If you want this thing to stay up there then you need to do it it right. You need to design the support for the unexpected, not the routine day to day undisturbed dead load. If your willing to take the risk of it working 99.9% of the time then go for it but I wouldn't want to drive across bridges, hop in elevators, or fly in planes that work 99.9% of the time. Do it right and plan for the unexpected and you'll be able to sleep at night. A good example is gas pumps. Pure dead load. Sit on a 12" concrete pad. Not moving a bit. But wait. What if a car bumps it? That's why they put the concrete filled steel pipes around all the pumps. Same with bridge supports. Can support the load fine until they get bumped, or are subject to large loads due to a flood, or an earthquake. So they make them bigger and stronger than required for 99.9% of the use.Millermatic 211Lincoln Precision TIG 225Century 250 MIGLincoln 225 AC Box (sold)I support my local welding store (Amazon, McMasterCarr, Cyberweld, EBay).
Reply:fab54, all of the points we've discussed have been explained and it has finally suck into my friends brain.  he's forwarded all the necessary info to a  structural engineer for further "enlightenment".again thank you all.     Dave.
Reply:Please let us know what the final design is. This is an interesting design problem.....Millermatic 211Lincoln Precision TIG 225Century 250 MIGLincoln 225 AC Box (sold)I support my local welding store (Amazon, McMasterCarr, Cyberweld, EBay).
Reply:i will.   thanks again.   Dave.