Pallet Weight Rating

[dmaier]

I am trying to determine the max weight a steel coil bunk can handle (weight rating). It is to use HSS tubing for the frame and wedges (saddle). However I am struggling with how to correctly calculate it's capacity. Would I individually analyze one piece of HSS, take the side walls as buckling columns and the top as a simple supported beam (the bottom portion neglected due to it resting on the floor)?

Or is there a series of equations that can help me in this calculation? Any help is greatly appreciated

Thanks

 

[dhengr]

Dmaier:
Are these for your own shop? What do the designs of your current coil bunks look like? It seems to me that you are over complicating the design with the lower frame made up of all of the pieces of 6"x3"x3/8" HSS parts, and their welded joints. Basically, the thin webs of the wedges pick up point loads from the coil. Then distribute them down, over a few inches of length, through a crappy weld detail (wedge web to HSS corner) into another thin web of an HSS, which then takes the load down through a radiused corner of the HSS and finally into the bottom face of the HSS, as a bearing load on the conc. slab, or soil. Why not just cut the wedge pieces from 8"x6"x.5" HSS pieces about 12" long, diagonally on the 8" face, so you ended up with two pieces, pieces which are about 2" near the center and about 6" on the outside end. The slope on the wedges should be about 15̊. Then weld the wedges to a 3'x3'x.5" or .75" thk. plate, with about 4" btwn. the inner ends of the wedges at the plate centerline. Lay this all out, to scale, so you see how it fits all of the coil sizes you deal with. Note, that wooden bearing pieces treat the coils much better, but of course, they get beat up over time and must be replaced. Also, for the big coils your conc. slab or soils must carry 11k or 12k/sq.ft.

 

[dmaier]

dhengr:

Yes this would be for my company's stock. Currently wooden bunks are used for standard storage. However as you have mentioned they get beat up over time. These steel ones are intended to be repeatedly used in staging so they will need to be more robust than wooden versions as they will constantly have product moved on/off of them.

There has been a first version using I-beam construction, however it is not well received as they are quite large and heavy, and hard to bolt down. So using the HSS was to 'thin' the overall design and lighten them to be more manageable as well less expensive to make. The largest coil is 80"OD x80"W and weighs 50tons.

This was not of my design, but up to me to see if they can handle the weight. I have not rated something of this nature in the past so I am struggling how to start with calculating it.

Thanks

 

[MikeHalloran]

I'd consider using more durable wood, e.g. oak, without changing the design.

Assuming you've already done that, and even tough wood is being beaten up:

Both the design in the sketch and as proposed by dhengr contain a lot of steel that isn't being stressed much at all, as in contributing to the weight but not to the strength.

Try drawing a free body diagram of each loading condition, to a uniform scale, using onionskin or CAD layers. Superimpose them all, then try to synthesize a structure that can carry an/all loads, and that only exists where loads are applied.
You might, for example, end up with 4 or 5 deep wedge pairs, connected by rebars just big enough to handle them as a group, with formed handles near the corners.

To protect the product, nothing prevents you from using '1x_' wood or HDPE as a replaceable/consumable covering on the wedges, secured by counterbored screws.



Mike Halloran
Pembroke Pines, FL, USA

 

[dhengr]

Dmaier:
What you showed might not be your own design, but I still don’t think it is a very good or practical design, and you might get a feather in your hat if you cleaned it up during your work effort. Reread my earlier post and sketch the details I suggested. Does that serve the same purpose and is it easier to fab. and use? What is the purpose of your lower frame made out of 6 pcs. of 6"x3"x.375" thk. HSS? Please explain. That is fairly complicated and difficult to weld together. Draw some sketches of the various welds on that frame, they are nasty little welds, for the most part. That’s expensive fabrication. Then, they don’t receive the load from the wedges very nicely either, and have a nasty weld detail too, draw that weld detail. Finally, the HSS takes the load down through its webs, from a round top corner, to a round lower corner which is eccentric w.r.t. the web where it finally contacts the conc. slab, not a good structural condition. Draw a FBD of that bearing condition and the web, and try making structural sense out of it. I’m not saying it can’t be done, but why make things difficult, for no good reason. The HSS is expensive steel in $$/pound when compared to a mild steel plate. The cost of the HSS and all the fab’ing. can buy you a lot of 3'x3' plate, and it’s a lot easier to weld the wedges to this plate, which is a lot easier to bolt down too. Alternatively, I’ll bet you could find a local saw mill which would cut you some 10' or 15' long 8"x8" timbers, and then rip them at 15̊ to make approx. 2" to 6" high wedges, 8" wide and 10' long. Do some of this study, sketching and thinking to clean up the design, or explain why you can’t clean it up, and show that in your next post. Then we can talk about stresses and cap’y. of this new design.