Load Bearing CFMF Eccentricity Question
Load Bearing CFMF Eccentricity Question
(OP)
I've got a condition where I have vertical load being applied eccentrically to cold form metal studs below.

As you can see, the one of the flanges is not fully engaged from the element applying the load (left generic on purpose but lets call it a 6" wide concrete beam for fun). When I designed the load bearing studs below, I simply applied a point moment to the studs below which = the vertical load times the 1 1/2" of eccentricity and came up with a reasonable design.
I have a cold form designer telling me that in cases like this, where one flange is not directly engaged by the element delivering the load (the 6" wide concrete beam), they take a a 50% reduction on allowable strength. They mention that this is not a code provision but something that they do. Is this justified? The flange to the side of the offset concrete beam will go into compression and the other flange will go into tension inherently even though it is not directly under the concrete beam.
Is there something I am missing that is so concerning about this that it warrants a 50% reduction in design strength? Let me know if I am crazy for thinking this should be easier than what it appears.
Thanks
S&T

As you can see, the one of the flanges is not fully engaged from the element applying the load (left generic on purpose but lets call it a 6" wide concrete beam for fun). When I designed the load bearing studs below, I simply applied a point moment to the studs below which = the vertical load times the 1 1/2" of eccentricity and came up with a reasonable design.
I have a cold form designer telling me that in cases like this, where one flange is not directly engaged by the element delivering the load (the 6" wide concrete beam), they take a a 50% reduction on allowable strength. They mention that this is not a code provision but something that they do. Is this justified? The flange to the side of the offset concrete beam will go into compression and the other flange will go into tension inherently even though it is not directly under the concrete beam.
Is there something I am missing that is so concerning about this that it warrants a 50% reduction in design strength? Let me know if I am crazy for thinking this should be easier than what it appears.
Thanks
S&T






RE: Load Bearing CFMF Eccentricity Question
In my experience, the moment caused by the eccentricity of the load will be small compared to the moment in the stud caused by wind load.
DaveAtkins
RE: Load Bearing CFMF Eccentricity Question
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Load Bearing CFMF Eccentricity Question
I did check the stud for the axial and the moment caused by the axial load.
Do you see any reason for the 50% in design strength mentioned by the CFS designer? Maybe to account for the load only being resisted by one flange and a portion of the web? Still feels like a hefty hit on allowable strength.
RE: Load Bearing CFMF Eccentricity Question
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Load Bearing CFMF Eccentricity Question
I do not even see the need of the track to drag the studs other flange along for the ride (although I can see it helping). Like I said, I feel that inherently the outside flange will automatically "move up" due to the applied point moment.
RE: Load Bearing CFMF Eccentricity Question
I also agree that their 50% reduction seems a little steep. It may require a heavier gauge track to ensure the legs travel vertically in unison, but it's not impossible.
RE: Load Bearing CFMF Eccentricity Question
Again, as in my above post, I feel that track does not even need to help in this behavior as it is inherent to the applied loading.
RE: Load Bearing CFMF Eccentricity Question
RE: Load Bearing CFMF Eccentricity Question
RE: Load Bearing CFMF Eccentricity Question
My spidy senses were tingling about the exact same thing. In part, it's hard to imagine a CFM industry acolyte taking such a seemingly conservative approach to a product within their wheelhouse.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Load Bearing CFMF Eccentricity Question
RE: Load Bearing CFMF Eccentricity Question
RE: Load Bearing CFMF Eccentricity Question
I reviewed the calculations sent over by CFS designer and was able to gain insight to their "50% reduction" in strength.
Essentially this eccentric condition makes equation C5.2.1-1 (AISI Spec 2012) the controlling equation for combined bending and axial load. This equation makes you consider moment magnification and makes you use a reduced nominal strength in your stud design. In a tradiation concentrically loaded stud this equation does not govern. After running this calculation with equation C5.2.1-1, I had about a 15% reduced strength in my stud design. I had not previously utilized this equation, but still a 15% reduction is not nearly as bad as the 50% they told me about.
Thanks,
S&T