Cold Formed steel Allowable strseses compare to Hot rolled Allowables stresses

[SKJ25POL]

I like to know if the allowable stresses for example for beam design for a cold formed still is lower or higher tahn allowable stresses for hot rolled steel.

Is it conservative in absense of having cold formed steel code, using the allowable stress values from AISC (hot rolled steel)?

Thank you

 

[DaveAtkins]

Cold formed steel members are thin, and therefore have a lot of issues with local buckling. So, no, you cannot just use the AISC Manual to design cold formed steel members.

That being said, for most cold formed steel design, you do not need the AISI Manual. Go to a manufacturer's website (such as Clark Dietrich), and you will find many design resources.

DaveAtkins

 

[PT999]

AISI Win is excellent software for this also.

 

[SKJ25POL]

DveAtkins,
Thank you for your input. But in general I am curios that for flexural members in general how is the allowables stresses compare to hot rolled

Fb = 0.6Fy and Fb=0.75Fy become lower or higher?
I have special situation that for the bending of a small cold formed steel plate, hot rolled allowable stress was used (Fb=0.75Fy), just want to know if it makes a big diference or not?
a 2' by 3' 1/4" plate.

Thank you

 

[KootK]

In that particular case, it probably doesn't make a big difference.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JAE]

For light gage steel - allowable stresses are affected mainly by the fact that light gage steel typically is thinner, and may or may not have stiffened edges.
Therefore, the AISI code has allowable stresses more governed by local and overall buckling rather than yield. So the answer to your question is that it
depends on the shapes you are looking for.

It also depends on the grade of steel used for light gage - i.e. Fy = 33 ksi vs. Fy = 50 ksi.

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[Bagman2524]

Cold bending makes the steel stronger, not weaker

Faith is taking the first step even when you can't see the whole staircase. -MLK

 

[SKJ25POL]

JAE (Structural)
The plate is 2'x2' and 1/4" thick the Fy is 34,800 psi
to find the thickness of plate Fb-0.75Fy was used. My question is it conservative or dangarious?

Trying to get in a simple language the difference is allowable stresses difiend in cold form and compare to hot rolled.

Thank you

 

[DaveAtkins]

For the situation in question, the allowable moment = 1.25*S*Fy/1.67 = 0.75*S*Fy.

So your design is correct.

DaveAtkins

 

[KootK]

That's pretty thick cold formed. You'll be safe using AISC provisions but I can't see any reason not to use AISI material properties and safety factors.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JAE]

I didn't know that flat plates 1/4" thick could be "cold formed". What is the forming? Not sure I follow what you are saying.

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[canwesteng]

I know in CSA-S16 there are limits to width to thickness ratios based on the yield strength of the steel, I think you could conservatively just derate the yield strength of the steel until these ratios are satisfied to get an idea of the strength of the section. But 1/4" does seem quite thick for cold formed.