Forming Channels from Thick Plates. Ducitility concerns?
Forming Channels from Thick Plates. Ducitility concerns?
(OP)
Hello,
We do a lot of work for this manufacturer. They have in house engineers but they aren't PE's in some states, which is where our firm comes in. We will stamp drawings/calcs for states they aren't PE's in.
Problem: They are taking 3/8" and 5/16" plate and bending them into channels. They word it like this "(C10) Designation represents a SS 3/8" formed plate to match C10x15.3 Channel."
The steel is SS type 304L.
Two questions:
1) Does this constitute a cold formed section now? Should I design with AISI?
2) More importantly, does this type of steel even allow cold forming? Are you allowed to form sections this thick? It seems to me you will get significant yielding at the outside corners since the sections are much much thicker than cold formed sections. Aren't there ductility requirements for cold formed sections? Are my concerns valid?
They've maybe done this once before or twice before but for some reason I didn't take issue with it. I'm going to talk to my boss about it in a bit but I was also like to hear what the community has to say about this.
Thanks in advance!
We do a lot of work for this manufacturer. They have in house engineers but they aren't PE's in some states, which is where our firm comes in. We will stamp drawings/calcs for states they aren't PE's in.
Problem: They are taking 3/8" and 5/16" plate and bending them into channels. They word it like this "(C10) Designation represents a SS 3/8" formed plate to match C10x15.3 Channel."
The steel is SS type 304L.
Two questions:
1) Does this constitute a cold formed section now? Should I design with AISI?
2) More importantly, does this type of steel even allow cold forming? Are you allowed to form sections this thick? It seems to me you will get significant yielding at the outside corners since the sections are much much thicker than cold formed sections. Aren't there ductility requirements for cold formed sections? Are my concerns valid?
They've maybe done this once before or twice before but for some reason I didn't take issue with it. I'm going to talk to my boss about it in a bit but I was also like to hear what the community has to say about this.
Thanks in advance!






RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
AISC V13, table 10-12 states that the minimum interior radi for up to 3/4" is 1.5T... or 1.75 for A514... no 316 or 304.
RE: Forming Channels from Thick Plates. Ducitility concerns?
going to download this.
Do you consider it a hot rolled section or a cold formed section?
RE: Forming Channels from Thick Plates. Ducitility concerns?
I haven’t worked much with forming SS, but done plenty with carbon stl., so just my 2 cents worth. How are they forming these channels, roll forming, more likely break forming, break press, how long? Can they apply any heat before/during forming? Forming to what inside radius vs. thickness? How do they treat the edge of the plates before forming, round them a little? Have you seem samples of this work and found any cracking? Make them do some testing on tighter radius bends and to more than 90̊; see when you start causing cracking. I’ll have to take a look at the ASTM Spec. and so should you. I assume the rolling grain in the original strip or pl. is in the same direction as the length of the channel, problematic? Small lengths would be better formed with the original rolling grain running across the bend lines. How are these formed sections being used? If the major stresses (bending, normal stresses) are parallel to the length of the member usually forming is not much of a problem. If you have significant stresses which might cross a forming crack that’s another matter.
RE: Forming Channels from Thick Plates. Ducitility concerns?
That being said it is extremely ductile with a Fy = 25ksi , Fu = 70ksi and 40% elongation (10% is minimum according to AISI and Fu/Fy >= 1.08). So it doesn't seem like ductility is an issue.
I think I am going to have to call them tomorrow and see how their engineers handle this because it is ballooning into a larger issue and taking up hours on a small job. But, I'd like to know how to handle this in the future.
All those forming questions I could not answer at this time but their shop is literally 3 miles from where I work so I could go look at it if I had to :).
Thanks for the response! From what I gathered the beam isn't going to crack or fail but I want to do this the right way regardless.
RE: Forming Channels from Thick Plates. Ducitility concerns?
Note that the bending and torsional properties would be different from a rolled channel, so they're not automatically interchangeable. In particular, some of the torsional properties are related to the largest-inscribed circle, which will be considerably smaller with the formed section since it doesn't have the tapered flange and fillet radius.
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
Yeah one of the requirements for appendix A is for it be part of ASTM A6, A500, A847, A924, or A568. I checked the ASTM book and it isn't. But the ASTM to be honest is kind of confusing because a steel can conform to more than one, especially when they have "referenced sections". But even after going through about half of them it doesn't appear as though its part of any of those sections.
I'm going to design it with AISI since it seems like the more applicable code. The fact that its very ductile quells some of my concerns of the residual stress. The AISC article I bought for 10$ didn't help at all haha. Oh well. I'm going to have to phone the fabricator and maybe I can go up and look at a couple pieces and maybe do some testing!
Thoughts?
RE: Forming Channels from Thick Plates. Ducitility concerns?
I think the visual observation would be good on some fabricated pieces to verify no cracking.
I wonder if you could also perform a dye test on a small percent (10%?) to check for micro cracking at the bends.
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
I would tend toward using the basics of the AISC Manual, probably using ASD for simplicity. The difference btwn. those and AISI, are that AISI pays particular attention to the thin plate buckling problem which exists on almost every element of all of their cross sections in every form of usage. That design spec. is driven by element buckling and cross section buckling which then leads to allowable stresses. Your material thickness and cross section fits the normal ranges covered by AISC. The fact that your particular ASTM Spec. is not explicitly listed does not change the basic Engineering Mechanics and Strength of Materials (Theory of Elasticity) which are the foundation of all our work. And now, it seems, even that has been rectified with yet another profitable Design Guide, without which we can’t be Structural Engineers any longer. The fact that all of the newer codes are so garbaged up with so many multipliers, divisors and other modifiers (load factors, resistance factors, reliability indexes, standard deviations dependant upon the day of the week and the moon phase, etc.) makes it almost impossible to find the basic governing principles of Engineering Mechanicals for all the other stuff, but they do still govern whatever we do, whether resistance factor is .91 or .89.
I would change the rolling grain orientation when I could. I would like to inspect shapes that they have already made for any cracking and for final material thickness in the bend area. I would have them do some sample bend testing to try to hone in on material thickness vs. bend radius and angle of bend vs. onset of cracking. JAE’s idea of some dye pen. testing is a good one, that kinda went without saying as part of my testing comments in my first post. I certainly would get a copy of that new Design Guide 27 on Stainless Steel. Without a doubt it will have much useful info. in it.
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
1) When I modeled it in RAM, I had to make a custom section. The custom section takes the form of a C section without lips. Ram recognizes this and applies the AISI code to it through design and I couldn't find ANYWHERE to let me change which code it applies to the section. This is what got me thinking about all this in the first place. I was going to check it with my AISC beam Mathcad sheet just to be sure. RAM was mostly for analysis not design.
2) The AISI code is for materials up to 1" thickness (according to Appendix A). The fact that they're bending the plats when they're cold obviously makes them cold formed. The AISI code seems to be a more in depth analysis but for the larger thickness I obviously don't have to worry about things like distortional buckling.
I checked out that AISC Design Guide, $60 for non-member. I'll have to see if my boss will let me get it. He's been doing this for years and years without a hiccup but I'm just curious what the design guide even says. I have a feeling it might not say anything that we haven't already discussed here, but who knows.
If I do get the design guide, I'll be sure to say whether it had anything useful in it or not!
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
RE: Forming Channels from Thick Plates. Ducitility concerns?
I would refer to:
ASCE 8-02 Specification for the Design of Cold-Formed Stainless Steel Structural Members
http://www.asce.org/Product.aspx?ID=2147487569&...
RE: Forming Channels from Thick Plates. Ducitility concerns?
Small job or large, unfortunately you don't get a choice but to learn how to do something properly. Frustrating when it is a small bit like this... Just imagine the trouble you'll cause (and save!) if you find they've been doing it wrong. *sigh*