AISI Cold-formed Steel Section

[Yt.]

Hi,

I've been working with the AISI S100-2007. I know how to use it but i'm not sure about the following.

Generally, the methods to get the stress/force distribution between the members of a structure depends on the stiffness of the elements, so is there a way to avoid to compute all the forces again once the effective sections are outputted from the code?

I've been calculating the forces, then the effectives sections and then the forces again and repeating this until I considerer the results are accurate enough. But is it the usual practice?

 

[KootK]

I've definitely not been updating my analyses for effective section properties although I can see a certain logic in it. Other than the odd multi-span joist, I struggle to think of anything else that I might have designed in cold formed steel that would have been statically indeterminate. Can you provide any more detail on the particular elements that you're investigating?

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.

 

[Yt.]

Thanks for the quickly answer KootK,

I'm not worried about my present work. It's just a wood deck supported by several cold-formed steel beams. Even when the steel beams have a slightly different length (because steel beams are supported in a curved edge) affecting their own deflection and thus the reactions of the wood deck over each beam. My members a sufficient to withstand this behaviour.

But i was thinking something more like a trussed structure with differents element sizes. (Not my case by the moment)

I developed a little software that do the calculations and it was easy to add a command line to input the effective size retrieved by AISI into my stiffness matrix. So when i had the updated matrix i just run my program again.

It would be harder to code an automatization of this by defining tolerances and mixing the different coded functions, so i'd wonder if it would be necessary.

 

[KootK]

Yeah, when I was trying to think of common examples of more complex CFS structures, trusses are what came to mind for me as well. But, then, most trusses are also statically determinate and, therefore, insensitive to stiffness variation in the individual members.

One issue that would complicate this in an indeterminate structure is that the geometry of the effective section would technically fluctuate with load. A simple span bending member may have 100% of its section effective along the outer thirds of the span but less so in the middle third. As such, it would be pretty challenging to account for the real effect in a robust way.

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.

 

[Yt.]

Sure, i manage that by dividing each in smaller elements (far away from finite elements), then calculating effective section for each segment. I don't know how to translate the general "truss-structure-like", always i write about it people tends to think that i'm talking about roofs. But i have made hyperstatic "Portal-Trusses" with wood and force distribution became sensitive to sawn lumber section and Elasticity.

Anyway, you guide me about what i need. Thanks! Because if there was a regular practice about it probably you may at least hear something about it.