Stiffened Cold Form Shapes

[ToadJones]

Does RISA 3D have provisions for specifying intermediate stiffeners on cold-formed cross sections?
Example being a cold formed C or Z shape with a longitudinal web stiffener rolled into the web or Flange.

 

[JoshPlumSE]

Toad -

Are you talking about where the manufacturer adds a mid-depth stiffener I'm not sure exactly what you're talking about. Does the attached picture show the type of web stiffener you are talking about? If so, then RISA does not currently account for this in the local buckling calculations of the web. You'd have to go with a program like CFS to do this. I would like to update the RISASection program to handle these types of stiffeners and calculate capacities and such. But, as of October 2012 it's not something that can be done with RISA.

 

[ToadJones]

Yes Josh...that is the type of shape I am referring to (similar anyway).

I am not familiar with CFS ?

I am trying to use CUFSM but it is pretty damn confusing./

 

[JoshPlumSE]

I don't know much about it either.... Other than it is a specialty Section Wizard type program geared towards the cold formed industry. One of our other engineers has some experience with it. Her experience is what planted the seed in my mind about updating RISASection to do similar calculations.

 

[ToadJones]

Josh-
Answer me this if you can....

I am investigating some cold formed shapes and looking at adding web &/or flange stiffeners.

The objective of the portion of the AISI Direct Strength Method is to make it easier to determine the elastic buckling capacities of cold formed shapes for local, distortional and global buckling (LTB) and then directly convert these to nominal axial and flexural member capacities.

However, if the member being analyzed is failing in pure flexural yielding then adding these stiffeners will really not be any help ...correct?

 

[JoshPlumSE]

I'm really not a cold formed expert. So, don't take my word for it. But, I think those types of stiffeners can influence the flexural yielding limit state.

If you look at section C3.1.1 Nominal Section Strength, you'll see that the flexural yielding capacity is based on the calculation of the "effective section" modulus which takes into account local buckling and stiffeners and such. Therefore, it is possible that the stiffener could add strength. Essentially allowing a larger percentage of the web to be "effective" as the extreme fiber of your section approaches yielding.