Cold Form yield stress

[tramyer]

Hi,

I wanna ask if cold form is limited only to gr.33 and gr.55?

Because upon seeing the AISI Manual Cold-Formed Steel Design 2002
Edition.

Especially how they calculate the effective sections. Was based only to gr.33 and gr.55. Is that true?

And in addition, I just wanna ask why they used 37.25 ksi (Why they didn't use the Fy which is 55 ksi) as compression force was that only an assumed value?

Cause I'm new to AISI and currently studying it.

thank you for those who will comment out there suggestions and their opinions.

Below is the reference pdf file.

Kind regards,

 

[BUGGAR]

A quick answer is you are not limited to those grades. The tables shown are for convenience and list the most common grades of steel found in commercial applications.
Somewhere in the AISI Specs it lists the grades of steel covered. Then you have to find out what grades of steel are available out there. If you see something like ASTM A513 (from memory, needs verification}, be aware that some ASTM specs cover several grades of steel and the buyer must specify what is wanted or possibly get a lower grade of steel.
And now we have ASTM A1011 that gives us light gage A36 steel.

 

[BUGGAR]

Oh yeah, you have to specify the steel grade in A1011 as well or you might get grade 30.

 

[wannabeSE]

I'd look at a latter edition. They are more useful with additional tables based on SSMA stud and track sizes. The next edition is based on the 2007 specification. The dimensions and yield strength in the example problems don't matter because they are showing methods for calculating. I think they are the same in the next edition. But, I never found any use for the 2002 tables. I don't know if those stud sizes were ever used in the USA. The SSMA sizes in the latter manuals are the "standard" sizes used today.

 

[structSU10]

AISI determined effective section properties based on the stress level present in the member. It is their way of accounting for local buckling - the profiles are so thin that everything is basically governed by buckling of some kind. In most instances, you estimate the stress for your given load, determine the section properties, then refine as required.

 

[tramyer]

how about the compressive force 37.25? Did the author just assume that how do I calculate that?

Can't i use its FY which was 55 ksi?

 

[Lomarandil]

Re-read SU10s response. In most cold formed members, you'll not get to Fy in compression -- local buckling doesn't allow it.

I suspect they calculated this stress level in the example III-1 they reference.

----
The name is a long story -- just call me Lo.

 

[tramyer]

I understood that. So that means. I have to estimate that? Until I meet local buckling? Is that it?

Are there any property tables precalculate aside from 33 and 50ksi fy?

Or any free software that calculates effective properties?

 

[Lomarandil]

I'm no AISI expert, but it seems designers usually compute the allowable local buckling stress (e.g. 37.25ksi) as one of the first steps of the design.

The most recent AISI (and maybe others) allow for calculation of these effects by the "effective width" method or the "direct strength" method -- Appendix 1 and 2, respectively.

----
The name is a long story -- just call me Lo.

 

[wannabeSE]

Look at example III-1. The 37.25 ksi is the buckling stress about the x axis for a 20' long member.