Bearing Strength of Uniformly Supported and Uniformly Loaded C Channel

[Trillers]

A client is replacing a modular FRP water tank with another of the same dimensions and capacity. The original tank was supported along its base (including cross bracing) by MC7 c channels sitting atop grade beams (plinth) 3' high. The new tank will sit on MC6 c channels.
The client has asked to confirm that the MC6 can safely bear the load.
In short what is the load capacity of a uniformly loaded and Uniformly supported c channel?
The channel will lay on a flange and the upper flange will support the tank.
Can someone lead me in the right direction to figure out the channel capacity under this loading condition?
The channels are adequately restrained against buckling and torsion.
Would it be proper just to calculate the web capacity simply as a structural section and neglect the flanges?

 

[JStephen]

If I understand your geometry right, you can take a cross section of the channel and treat it as a column or beam-column, depending on your load assumptions.

 

[XR250]

I guess that is the tough part. How much eccentricity do you assume on the flange or do you just pretend the web supports the equipment as a knife?

 

[racookpe1978]

Again, no dwg, photo, sketch, or scanned image!
Is the old (and new) FRP tank rectangular, square, or round?
What diameter of tank?
Are there interior supports crossing under the FRP bottom floor (stretching between the MC7 under the tank walls) or is the tank only held up by its exterior (?) walls?
Are there any cutouts or large holes in the upper MC7/MC6 channel flanges?

 

[SlideRuleEra]

With a look at the details, there may be a solution where no calculations are needed. For many years there have been two sizes of MC7:

MC 7x22.7, Web Thickness: 0.503"
MC 7x19.1, Web Thickness: 0.352"

Likewise, there are five sizes of MC6. The heaviest is MC 6x18, Web Thickness: 0.379"

If the existing channel happens to be a MC 7x19.1 and the replacement is MC 6x18... it works.
If the MC6 is lighter, calcs based on detailed loading, etc. are needed.

If the existing channel is MC 7x22.7 and is heavily loaded... probably none of the MC 6 will work. But in that case calcs (again based on the detail loading, etc.) could prove otherwise.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Trillers]

JStephen and SlideRuleEra - thank you!!

JStephen I had already treated the cross-section as a column and analyzed for shear since the beams will be well braced so the primarily load to analyze would be shear ...and it worked out OK.

SlideRuleEra - you are a genius!! I never thought to compare as you suggested and sure enough the existing is MC7x19 and the proposed is MC6x18.

Now I can get some rest.

Thanks guys.