Formed Steel channel 1

[kaffy]

Good Afternoon fellow engineers,

Is it common to use formed C channel rather than hot rolled C channel?

The reason I want to use a formed C channel is because of the quantity as sheet metal fabricator can laser all the slots.

let's say I am using the same material, same dimension properties.
Do I need to add a further strength reduction factor while doing my calculations as in hot rolled material properties are more uniform.

Also I am worried about the cracks at bends especially if the material is 1/4" thick. Can anybody guide me in right direction?

Thank You
KD

 

[WARose]

When you say "formed" do you mean cold formed? If that is the case, such a section needs to be checked as per AISI's code. The allowable stresses are different based on the cold working.

Also I am worried about the cracks at bends especially if the material is 1/4" thick.

Usually-at that thickness-you are talking a AISC shape. The cold formed stuff is typically much thinner.

 

[kaffy]

By formed steel, I meant creating a flat pattern first and then bending it with a sheet metal brake
(not the one where we pass the sheet through rollers).

 

[kaffy]

I see the confusion. My apologies, I meant the bent profile not the cold formed steel.

 

[GC_Hopi]

To clarify there are automated processes for fabrication of angles, C and W sections. Link It may not be economical to do flat sheet. You should check with some fabricators that are local to the project area.

 

[Agent666]

Bend radii is key here, a sheet brake offers very little control over this and potentially concentrates strain hardening immediately adjacent to the 'blade'. More of a sharp bend locally vs constant radii around the entire curve you're trying to create.

I saw someone once bend reinforcement incorrectly using a method like sheet brake, when delivered to site the bars quite easily fractured due to the strain hardening this method created. I'd avoid depending on how you're using the end product.

In our plate standards in NZ, there are tables showing the appropriate former diameters to cold bend around. I'm sure there must be something similar in North America, but you might be looking at 3+ times the thickness of the material depending on the grade, so as not to overstress it. This results in quite larger bend radii, much larger than equivalent hot rolled sections and affects the final form of the section you can achieve. Table below provided for reference: -

https://engineervsheep.com

 

[dauwerda]

If your fabricator has a tube laser cutting slots in hot rolled channel won't be a problem either.

https://www.youtube.com/watch?v=QoF1nxKW0vw

 

[kaffy]

Hi guys.

Thank you for the suggestions. The reason why I want to stick with cold bending is because I can have any flange size/web size. I can also customize the shape and add an extra flange at 90degree to get higher section modulus.

 

[kaffy]

Thank You @Agent. So that table is actually incorporated in your structural steel design handbook?

 

[DrZoidberWoop]

A structural channel is not the same as a piece of twice bent plate (The taper toward the channel toe in a hot rolled section, for example). Also consider fabrication tolerances and QC. The acceptability of what you're trying to do depends on the way you intend to use the "channel."

Typically, you won't need to worry much about cracking of 1/4" steel during cold bending, but results will vary between fabrication shops, as usual.

"The reason I want to use a formed C channel is because of the quantity as sheet metal fabricator can laser all the slots." If your holes are going to be in the web of the fabricated channel, this could work, but if not, you will inevitably find that those pesky holes often don't end up in the right spot after bending, so consider slotted holes to account for variable bend radii.

 

[dauwerda]

the AISC steel manual has a very similar table to what Agent666 posted. It is table 10-13 in the 15th edition manual.
The table references Brockenbrough's article in the Engineering Journal, "Development of Fabrication Guidelines for Cold Bending of Plates".
This is available for free from AISC is you are a member:

https://www.aisc.org/Development-of-Fabrication-Guidelines-for-Cold-Bending-of-Plates