Box steel strength rating?

I have acquired a pile of 2 inch by 6 inch by 1/8 inch wall rectangular tubing. I want to use it for the legs of a stationary hoist or gantry and put an I or H beam across 4 of them (set up like a swingset). I know there is a chart somewhere for calculating the vertical load capacity, anyone know where a copy could be found? Thanks in advance!

I believe it would take a professional (skilled, experienced) structural engineer to give you any safe, meaningful load rating as there are so many variables and any failure would probably be a safety issue.
1. columnar (straight in line with the tube) load data is not useful as I understand what you are doing, the load will be also in bending mode.'
2. 1/8 (or 11ga)thickness precludes deep penetration welds. Although you can get good looking welds, the stress around the weld and the thinness of surrounding metal doesn't make for a completely safe load bearing connection unless you use plates and gussets at the joint and even those parts can cause too much rigidity or weld stress to be safe.
3. 1/8 (low carbon mild steel?) is much more susceptible to rust-through than, say 1/4 inch thick stuff. 30 years from now, some poor fellow may come to grief under the corrosion.
4. What is the condition of the interior of the tubes and seam welds now?
5. Extreme loading of any design can be caused by choosing too small of wheels/casters that can't roll over floor cracks or debris while under load. IMHO, the caster/wheel should be rated for the entire rated load of the design, not 1/4 the load.
It is easy to get rated beam strength (bending) load from books for the main beam as that data is from tables of unrestrained beam end data. Remember the load may not be distributed equally between the two supports, most of the load may be on one leg/support system.
Please do not be offended if I have suggested anything you already knew, I got interested because of this useful, fun project. I hope to make one someday soon, myself. Leonard

Hi Brent,

If you get the information you need, would you please post it, and particularly, tell us how and where you got it? This general type of question comes up frequently enough that I know that many of us don't know how to go about finding this information.

Thanks, Stan

(quoted from post at 09:02:43 02/12/09) I believe it would take a professional (skilled, experienced) structural engineer to give you any safe, meaningful load rating as there are so many variables and any failure would probably be a safety issue.
1. columnar (straight in line with the tube) load data is not useful as I understand what you are doing, the load will be also in bending mode.'
2. 1/8 (or 11ga)thickness precludes deep penetration welds. Although you can get good looking welds, the stress around the weld and the thinness of surrounding metal doesn't make for a completely safe load bearing connection unless you use plates and gussets at the joint and even those parts can cause too much rigidity or weld stress to be safe.
3. 1/8 (low carbon mild steel?) is much more susceptible to rust-through than, say 1/4 inch thick stuff. 30 years from now, some poor fellow may come to grief under the corrosion.
4. What is the condition of the interior of the tubes and seam welds now?
5. Extreme loading of any design can be caused by choosing too small of wheels/casters that can't roll over floor cracks or debris while under load. IMHO, the caster/wheel should be rated for the entire rated load of the design, not 1/4 the load.
It is easy to get rated beam strength (bending) load from books for the main beam as that data is from tables of unrestrained beam end data. Remember the load may not be distributed equally between the two supports, most of the load may be on one leg/support system.
Please do not be offended if I have suggested anything you already knew, I got interested because of this useful, fun project. I hope to make one someday soon, myself. Leonard

Click to expand...

Thanks for the feedback, all very valid points. If they didn't all apply to me they will likely apply to someone reading it later.

I am planning on building a stationary unit, not on wheels/casters. It will require moving the carrying object rather than the crane when hoisting and moving something but it is the only way it will work in my shop.

Also, that will prevent it from going outside into the elements, and from people wanting to "borrow" it. I don't mind loaning things out but all too often they come back broken, or a month late, or not at all.

I will continue to do some research and post back if/when I find something out.

Well I found a great reference manual online, and was even able to find my box steel with the correct wall thickness. However I do not know how to interpret "KIPS" and "KSI", something to do with shear strength blah blah blah.

Anyway, here is the link if anyone wants to look.
http://www.steeltubeinstitute.org/pdf/brochures/beam_load_table_bro.pdf

That bla bla bla might be what saves your hide when working under it LOL or the person that talked you into borrowing it, or some other person after you are gone etc.

You might want to see if any AISC reference materials will provide some additional information, on the shape you have you can find older editions of their manual of steel construction handbook on e-bay, been awhile since I looked in one and forget if they provide and strengths and statistics of steel materials, but they will ID the shape and weight per foot. Good reference material for steel though costly to own, the new manuals are a few hundred bucks.

Personally, I think any time one fabricates a hoisting device, no matter how small, they should know by virtue of mathematical calculation what the safe working loads are of the component making the span, loads imposed onto the floor, or base of the hoist etc etc., including a safety margin, same information should be stenciled and painted onto the equipment in a conspicuous place. Some people balk at this, I know what I am doing, don't need no engineer to calc it out or do some rudimentary analysis to at least provide an idea of what you are dealing with.

Often times people will eyeball these things and not consider other factors, and it may never be an issue, most times you don't even know the real weight of the item you hoist anyway, all good reason to know the equipment is capable well beyond what your actual use is.

See what you can find in AISC, might be something there, not exactly sure of the shape you have, sounds like it could be tube, but you say box, you definitely want to ID the shape if this piece is not something previously fabricated. It would be a good idea to rough sketch your fabrication plans, detail all steel, fasteners and welds to be used, and just pay an engineer to analyze and calc it out so you know what you have, something like might be worth 1-2 hours to an engineer, or just wing it, be careful and don't let anyone borrow it. I spent a lot of time in my career doing just that, could not chance the risks, every dime I spent on the engineer was always worth it, some are fantastic to deal with, field and application orientated, will work with you or what you have, been there many many times.

I designed and built this crane. 24-foot span, 40-foot travel (powered).
<a href="http://smg.photobucket.com/albums/v512/Chyrel/cranes/?action=view¤t=Hoists-1.jpg" target="_blank"> </a>
<a href="http://smg.photobucket.com/albums/v512/Chyrel/cranes/?action=view¤t=Truck-1.jpg" target="_blank"></a>



But, I had a friend who is a PE bless every detail of it! Auto-Cad and e-mail made it so easy to get his approval.

How long are the pieces? Do you know that they passed inspection? 1/8" seems light to me but it depends a lot on the design. I knew the guy that invented the Jay-copter that was at the 1964 N.Y. worlds fair. It carried 16 people 125 feet in the air. None of the tubes in the triangular boom were thicker than 3/16" but then again his brother designed it, who was a structural engineer. There is point between using too thin of a wall and using something solid or too thick. Often times tubing will be a lot stronger than solid because the solid material will weigh too much which causes deflection. Best to talk to an engineer, I think. Dave

It is all new material left over from fabrication work a welder/neighbor did at a local factory. He built a bunch of HUGE roller tables that hold jigs for making trusses, they put the wood and truss plates into the jigs, then this GIANT roller comes over the top, running on RR track on floor, and roll-presses the trusses together. I figured if it could handle that multi-ton press I could make something useful out of it. Most pieces are 12-14 feet long. Scrap price was so low he just let me have it for helping him clean up and haul it out. I suppose I got 12 or 16 of them.

Thanks for sharing pictures. A good crane is so necessary and expensive and it looks like if you mishook the sling/chain you could lift the whole truck with the load. Are there any cross tie rods between the support columns? Call me green-eyes! Leonard

That is ironic, I know the exact set up you describe, we had a truss plant at the lumber yard where I worked years ago, I used to ride the roller and work in there when deliveries were slow, helped install the equipment when they built the plant and did a fair amount of work on one of those tables, including setting the jigs, the saw that made the smaller web pieces was interesting. The roller is what presses the splice plates against the table, they set the pieces, hammer the plates at the joints, lift the joint, toss one underneath, then roll, then feed through the final double roller out the slot in the building to the outside rollers for stacking and banding. If the material you have is anything similar to what this table was made of it would be wise to see if the use you have for it will work structurally, hopefully it does.

Brent: Kips is Kilopounds, or in other words, 1000 lbs. KSI is Kilopounds per Square Inch--just good old PSI x 1000. Beyond that, I'll second (and third, and fourth) the recommendations to get a good mechanical or civil engineer to look over anything you do, particularly if it's going to be used where catastrophic failure could endanger someone. This type of project can look simple, and often IS simple, but even competent engineers don't know everything--most engineering formulas are distillations of hundreds of years of trial and error, and do not represent "absolute truth" so much as the best educated guesses of thousands of bright people. The education that went into those educated guesses cost many lives when those guesses were wrong--it would be a shame to add yours or someone you care about to that total.

Hi Leo!
Yes there are five 4-inch sch. 80 pipes welded to the top of the main rails. The pipe braces at each end have tabs welded to the pipe and two 3/4-inch x 6-inch lag bolts into the 6 x 12 building columns. The center posts of the bridge crane are 8” x 8” x 1/2” box tube. The four corner posts of the bridge crane are 4-inch sch. 80 pipe also attached to the 6 x 12 building columns.

If you are going to use the box tube for the legs you need to worry about unbraced length (the distance from one horizontal support to another).

The AISC has formula that gives you the maximum load that a specific length of column can take before it buckles. To be on the safe side you want to ensure that any one of the two legs one each side can take half of the entire load with a safety factor of at least 8 to 1.

1) How tall is the gantry going to be?

2) What is the grade of the steel tube. It should be marked on the outside of the tube. I.E. A500. This will give you the Fy of the steel. That number plays into the buckeling equation.

3) The table that you found are for using the tube as a beam NOT as a column. These equations are NOT interchanged. Bad things happen.

4) What angle are the legs going to be at? If they are not straight (up and down) then not only are they acting as a column but also as a beam. The equations get a little bit trickier.

5) Will the load always be in the center of the span or will it be on a trolly? If it is on a trolley in means the legs need to be sized to take more load then if the load were always in the middle.

As everyone else has said, make sure someone runs the numbers on this structure.

Hope this helps.

Thanks! Those things had come to mind but I would have to dig out some OLD textbooks to even attempt...so I guess I need to break down and call my engineer brother-in-law...my dreaded last resort as I hate owing him favors - he usually has bigger ones than I at payback time.