Stainless Design 1

[PEinVA]

Hi,
I have a building where the architect wants a cant. canopy with WTs flanges down and glass hanging from below. The longest dimension of the cant. WT is 13'. Using ASTM A992 carbon steel, a WT9x35.5 is at full bending stress and deflection limits. (Fy = 50 ksi). The only information I've found about using stainless for structural design is that type 304 is usually used. This yield strength (Fy) is only equal to 39 or 42ksi. This obviously changes my stress limits and would cut back on the length of the canopy, and not make our client happy. Is there another grade stainless steel that can be used and easily welded to a carbon steel HSS section? I am on the SSINA's website and find it very confusing and I feel no REAL information is provided. Let me know at your earliest convenience and please provide any references or suggested reading. Thanks for your help!

RC

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[EdStainless]

Look at using a lean duplex grade. Either Outokumpu's LDX2101 or Allegheny Ludlum's AL2003 will give you a minimum yield strength of 65 or 70ksi depending on section thickness.
I have seen some huge architectural jobs being done in these grades. Also both are much more corrosion resistant than 304. The LDX2101 is the lower cost of the two.

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Plymouth Tube

 

[mcguire]

I concur. See Allegheny Ludlum's website for an interesting article on the world's largest stainless roof, for which I specified grade 2003.

http://www.investquest.com/iq/a/ati/ne/news/ati110707.pdf

http://www.alleghenyludlum.com/

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[PEinVA]

Thanks for the response EdStainless and mcguire, but I'm still at a loss for how to actually go about designing stainless steel members. Most articles I've read about it say, DON'T design it in a way similar to Carbon steel due to differing mechanical properties. How do we go about designing a stainless structure when there are no codes/guidelines to use in North America. I've found some European stuff and British code specifically seems to really handle this as a structural item more than architectural (how we seem to consider stainless steel here in the US).

Thanks again guys.

Rick

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[mcguire]

Sorry, Rick
I don't know which codes to refer you to. 2003 or 2101 behaves just like high strength, low alloy steel, so I think the warning to not consider it like carbon steel does not apply here. Yield strength, modulus, etc.

Maybe some our more code-savvy memebrs will help us here.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[PEinVA]

Michael,
I am reading up on 2101 and I found this in one of the PDF documents on Outokumpu's website.

"However, it is important to point out that both austenitic and duplex stainless steel behave somewhat differently to carbon steel regarding structural design, particularly
regarding instability and local buckling. Design recommendations for stainless steel are available, such as Design Manual for Structural Stainless Steel, published by Euro Inox [5]."

Obviously the Euro code is useless to us. The SSINA is also useless for any design information.



RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[mcguire]

It sounds like the people who want to sell stainless steel have some work to do. Which codifying body would you want to see do this?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[PEinVA]

Obviously, AISC doesn't want anything to do with this because of the paragraph above. They want to stick with the stuff they've used over the last 100 years. Although the code officials in Britain and Europe have added information to the typical steel code for reference to stainless steel design from what I read. ASCE has put out something on Cold Formed Stainless Steel Design. (SEI/ASCE 8-02). I don't know who should do it. But I'm sure the stainless steel industry would LOVE for it to be done.

I also found information on Bristish Stainless Steel Association's website which states the deflection of stainless steel beams increases at higher stresses.

See

http://www.bssa.org.uk/topics.php?article=126

for information

Thanks again for the response.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[EdStainless]

An option is to contact Catherine Houska at TMR in Pittsburgh.

http://www.tmrstainless.com/index.html

They are a consulting firm with extensive experience in the applications of stainless steel. Catherine specializes in architectural applications.

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Plymouth Tube

 

[JKW05]

See ASCE 8-02:

https://www.asce.org/bookstore/book.cfm?book=4286

 

[PEinVA]

That is for Cold Formed Stainless Steel. Not Rolled Steel. I'm working with plates with thicknesses over 5/8". Thanks for the response though JKW05.



RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[PEinVA]

Back to this stuff,
So now the architect has changed his mind about the design and I have to design the item again, and I'm realizing that creating a moment connection at the base of the cantilevered upside down WT's is going to be a messy connection. I'm having the WT come back to a HSS12x8. This will be made of carbon steel (Fy=46ksi), and the custom WT out of stainless 304 (Fy=42ksi). I'm going to use 309 weld material to help prevent damage to the chemical make-up of either material.
While this connection will be "interior" I am worried water will still get into the area if snow drifts sit where the canopy extends from the facade. If water hits the welded area there is a concern of galvanic action and corrosion at the weld occurring. I know I could paint this after the weld is complete to help protect it, but is there some other permanent protection one can use?

Thanks guys.



RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[PEinVA]

I just looked up the ASTM designation for the 304 plates and I found 2 different designations. ASTM 276 and ASTM 666. Both of these show a minimum of Fy=30ksi. In reviewing information from a SSINA (Specialty Steel Industry of North America) it shows austenitic stainless steels 304 (S30400) Fy = 42 ksi. Why is there this difference in information? I was using the Fy=42 ksi, and now if I use 30 ksi, my design won't work.

Stupid architects, must have stainless steel. Carbon isn't pretty enough painted.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[Stl63]

304 plate is covered in ASTM A240, as far as property minimums go, 30ksi yield and 75ksi tensile. I do not believe there is an ASTM covering rolled shapes of stainless steel. Though there is a company or two that rolls 304 shapes.