C-Channel Configuration

[Sam Low]

Hi All,

There is a 600 N/m distribution load applied to the same size of channel but in different configuration. Herewith attached the sketch for your reference. Which configuration is better?

In my opinion, it will be more or less the same since the contact area (Highlighted in yellow colour) is almost the same.

Hope you all can help me out on this.
Thank you!

 

[JohnRBaker]

I would say 'B' and for more reasons than the obvious. I agree, structurally, it's pretty much a wash (no difference), but from a housekeeping point-of-view, with the legs turned-down, no debris nor foreign objects can collect in the 'open channel'. It's just cleaner and easier to keep it that way.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
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The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[desertfox]

Hi Sam Low

Better from which point of view? From a loading point of view 'A' is better in my opinion because there is no bending stress to worry about unlike the 'B' configuration which is only resting on the base by the vertical legs.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[SnTMan]

Lots not to know here. Is the channel acting as a beam, i.e. cantilever or otherwise supported, subject to bending? Or is it fully supported, i.e. laying on a slab, subject to compression only?

To JohnR's housekeeping point, legs up, easy to clean out, legs down, less so. Ignoring end caps, if any

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Compositepro]

I assume the sketch is an end view of a beam at its point of support. In that case the legs should face down so that they are under tension. If they are under compression the legs will buckle easily because the tips of the legs will see maximum compression and they are not braced against lateral buckling. You can demonstrate this with a steel tape measure. It will support itself in a cantilever with the edges up but will not with the edges down where the edges are under compression.

 

[LittleInch]

Makes no sense. What is the channel doing if its resting on a surface.

You say 600 N/M but show a 600 N point load.

Needs the side view also.

And an explaiation of what this is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sam Low]

Hi all,

I would like to discuss this from the perspective of resistance to bending moment.

This channel is used to carry the CO2 gas cylinders weight only. In order to make it easier to understand, I have summarized the distribution load to 600N/m. Please find the attached for your reference.
I was wondering configuration A or Configuration B would be better in terms of design wise.

In my point of view, the bending stress is only considered for bending momement and structure moment of inertia. Does it mean either way is acceptable ?

Thanks for your explanation in advance!

 

[LittleInch]

Ah ok, this is a bit different.

So basically this is a free standing beam resting on two supports.

What you have is a set of point loads, not a UDL.

So is your question "Is there any difference in bending moment from the orientation of a C channel up or down."

I would have thought that the BM would be much better if you rotate the C channel 90 degrees on the basis that the web is bigger than the up stands, but much depends on the specifics of your channel.

This little tool allows you to rotate the channel 90 or 270 degrees? Input your data and see what happens. and let us know.

https://calcresource.com/moment-of-inertia-channel.html

Only other point if you want to go as per your sketch is the bearing pressure on the supports is lower in option A than option B


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rb1957]

surely the difference between legs up or legs down is that in one config the base is in tension and in the other it is in compression.

The base in compression will have a higher allowable than the legs and it'll have a lower stress than the tips of the legs (the NA is closer to the base).

The flip side is the base in compression means the tips of the legs are in tension, and higher stress than the base.

I'd've thought that tips of legs in compression would be limited by crippling stress and so have a lower allowable moment than base in compression.

another day in paradise, or is paradise one day closer ?

 

[Sam Low]

Hi LittleInch,
Yup, you are right, Thanks for clarification of my inquires!

I agreed with you that the C channel at upright position will have lower bending stress due to the high inertia of moment.
I tried to use the tool you given in the link. Both option A and B given the same inertia of moment (If I am using it correctly).


Hi rb1957,
Agreed. It should have limited by the crippling stress at the legs in configuration B. However, I think the bending stress in C-channel structure for both configurations are still the same.

 

[LittleInch]

I'm not surprised that the orientation up or down makes no difference, simply that the compression and tension forces change from one to the other.

So there is not difference in stress terms between configuration A or B

So it's all about the point load / pressure on the supports.

So is the connection point really a pivot / point load or are you really bolting this thing down and creating instead a fixed beam?

Or the other considerations such as in configuration A will your channel fill full of dirt / water / animals / leaves.

So purely on the basis of ease of construction and keeping it clean I would go for configuration B.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rb1957]

sure the applied stress "just" changes sign, but the allowables change significantly (or not, depending on the section).

another day in paradise, or is paradise one day closer ?

 

[Compositepro]

As I pointed out earlier, compressive buckling at the point of maximum stress may become the limiting factor rather than yield strength. This depends on the geometry of the channel as to whether or not it will occur. But legs up will always be more prone buckling failure than legs down, assuming constant steel thickness.