Angled and Cantilevered shelf - max load? 3

[beattsmjk]

Hi,

I am trying to design a simple racking system for a small IBC (container that is to hold 250Kg of liquid).

The rack it sits on will hold just one box but will need to angle down approx 10 degrees so that the entire contents of the box can be drained. box is 800 wide x 600 deep x 830 high approx.

I was thinking of making the frame out of standard mild steel channel or box section but am unsure of how the material sizes I need to prevent the shelf from shearing at its rear support, which I was either going to weld to an upright or more than likely bolt to.

I have attached a pdf showing my idea. (ignore the fact I have shown it three boxes high, I intend to go one or max two high).

many thanks for any advice.

 

[kingnero]

The hooks (parts A+B+C) will be bolted to the I-beams?

Draw a free body diagram for the hooks, and combine+divide the shear force and moment over the bolt group.

Dimension the bolts for shear and tension.

For welding, it's essentially the same idea but a bit more work. still pretty basic in this case.

Note:
I wouldn't use 10 degrees, if it's fluid it'll run to the lowest point with a much lesser angle. Thick oil maybe slower, but it'll get there eventually I'm sure.

 

[beattsmjk]

Hi,

Yes Parts A,B,C will be bolted to the upright I beam.

I know what a free body diagram is but i'mm unsure of how to go about combine/dividing shear force and moment over the bolt group. Any tips would be greatly appreciated.


I agree with the 10 degree, we could probably get away with less, but the liquid is quite viscous (consistency of double cream).

 

[kingnero]

Draw the FBD with the forces and upload it, and I'll see maybe tonight, probably tomorrow evening for checking your bolts - shouldn't take too long.

 

[beattsmjk]

Sorry Kingnero,

I wouldnt know where to start in drawing an FBD!

I understand what they are but not how to construct one.

The only info I can offer is the weight of the box (full) = 250 Kg
The angle of incline - say 10 degrees
The material used to support the box (x2) is 50x50x6 mild steel box section, welded to a flange plate which in turn will be bolted to an upright I Beam. The arm is approx 615mm long

The Bolts I would intend to use are probably M12's
The box is 600mm deep x 800mm wide x 830mm high


Sorry if this isnt enough info for you.

 

[hydtools]

Google it to get started:

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=tp1502

Ted

 

[drawoh]

beattsmjk,

Are you an engineer, or a drafter?

You are asking very basic questions. This sort of calculation should be done by someone on site who can see everything, and who knows what they are doing.

How catastrophic will it be if this thing fails? A container with 250kg of liquid in it will hurt, even if the liquid is not something dangerous.

You should be wondering about your cantilevered vertical post, especially at the base.

Also, the weight of your liquid is not the only load your structure will encounter. How do the containers get on the rack. A search on Eng-tips for forklifts can be entertaining as well as informative.

JHG

 

[MiketheEngineer]

This is truly Statics 101.

Suggest you hire a professional licensed structural engineer so you don't get someone hurt.

But at about 500+/- lbs - it will not take much to make it work.

 

[beattsmjk]

Drawoh,

I am an instrumentation engineer but because I work for a small company need to turn my hand to other areas from time to time. I feel that you are being quite patronising in your approach to my request for help.
What may seem basic to you, may not to others and if roles where reversed I would not adopt such a stance.


I will in know way have this construction built without being 100% sure of it's capability in safely holding the load, but wanted to get a heads up on how this is calculated so when I do go to an engineering company who deal with this kind of thing I have an understanding of how things are worked out.

If it were so simple as you say, how come you are unable to point me exactly in the direction I need to be heading?

Yes I am fully aware of the perils of forklift drivers.

The design is based on the racking that is used widely to hold stock steel, often rated at much higher loads than I would be dealing with, but I appreciate my loading is slightly top heavy due to the angle of incline.

Thanks

 

[nuche1973]

This is an interesting FBD. Not only do you have the vertical forces to consider, but you also have a column that is basically a cantilevered beam and it is all dependent on where the rack is located. For starters, I have included a red-line review of your initial drawing. I also noted some websites that cover statics problems and FBD's. As stated before, you may want to consider additional assistance. I hope this helps.

There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.

 

[nuche1973]

Opps forgot the pdf. It has been a long day.

There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.

 

[beattsmjk]

Thank you for info nuche. I will indeed seek further assistance as it is looking increasingly more complex.

 

[drawoh]

...

If it were so simple as you say, how come you are unable to point me exactly in the direction I need to be heading?

The problem, as noted by MiketheEngineer, is that you are asking questions about statics. This is the basic thing you have to know to understand the forces involved. Then you have to learn some mechanics of materials so that you understand the stresses, then you have to learn machine design so that you understand the bolts and the welding. After that, you need some practical experience, preferably with an experienced designer or engineer looking over your shoulder. It is not as if I could take over your job.

I can look at your drawing and work out bending moments, but all that is is a few details I understand. We cannot see the whole picture. It is possible or even likely that there is some detail that makes the whole analysis wrong.

Think back on the first month or so after you graduated from college. How good a job did you do on the very first engineering task you were assigned? Was anybody's safety on the line.

JHG

 

[kingnero]

Maybe not the wisest thing to do, but I said I'd have a look...
You need to check the values in the calcs, (length, point of G, factor of safety, ...) but with this you'll know how to start yourself.

As mentioned before, the connection of the vertical post to the horizontal footings will be much more stressed, and will need a more detailed design.

 

[nuche1973]

kingnero:
nice add-on. I'd use a factor of safety of 2:1.

There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.

 

[beattsmjk]

Sorry Kingnero, I've been out of the country the past few days.

Many thanks indeed for your efforts, I would have never have got that far.

 

[kingnero]

Also - and this is why you need someone on-site to help you - you need to check the threads for their strength: if you're threading the I-beam, it need to be thick enough so the bolts can develop their full strength (there's no point in drilling & tapping a 4mm flange for a M12 bolt, for example).

I didn't think of it right away because it seems logic when looking at the thing, but from an on-line description you'll miss sometimes the obvious.