Welding C Channel to form I-Beam

[nickking2785]

Have a question for you guys. Came across several 12’ pieces of c-channel from a job. This winter would like to work on making a 30’ I-beam out of some of them to be used on a patio overhang.
Would weld the c-channels back to back making an I-beam out of them. I would stagger the joints at 6’ intervals.
Anyone see a big problem with this? Solid weld on top and bottom.
Thanks guy’s appreciate the input

 

[ncornilsen]

A solid weld along the top and bottom is not necessary... you could easily do 3" welds, on 9" centers and get 99.9% of the strength.

I would also recommend making a box section instead of an I-beam, as I beams are a bit noodley to handle if you can't lift them from above, etc.

For the joints, I'd be more concerned about landing the joints on a support/post etc than I would be about staggering them. This makes the weld to the next member much less critical, and probably easier to hide.

 

[Firebrick43]

How big of channel and what kind of span are you thinking is the most important info needed

 

[joe_padavano]

As noted above, a series of 3" welds for the back-to-back joining will be fine. The real issue is that the **** joints between the 12 ft sections need to be fully welded with full penetration, especially at the caps. Use a runoff tab to ensure you don't get undercuts at the edge of the flange. Trim these tabs off after welding to maintain the original profile.

 

[CraigStu]

Someone w/ more experience than I can probably offer a solution. What I can relate is about weld distortion. I welded two pieces of 8ft angle w/ a 1/2 in flat in between to form a C. It was used to cap the end of a wall. I did a lot of small 1/4-3/8in tacks every 6-8 inches. Got it all tacked and it looked fine. Then went back and made the tacks into 1-1.5in long welds. That thing turned into a noodle. I got on the web to understand the technique of heating a certain spot on a tube to straighten it. Spent WAY more time straightening than the initial welding.

 

[ez-duzit]

...weld distortion...

This is why you would buy I-beam, rather than try to weld that.

 

[theoldwizard1]

A solid weld along the top and bottom is not necessary... you could easily do 3" welds, on 9" centers and get 99.9% of the strength.

I am not so sure about that statement ! It has been over 50 years since I had classes on this topic, but as I recall ...

The strength in an I-beam (also called H-Beam), is in the top and bottom flanges. Look at commercial building flat roof trusses or even "wooden" I-beams. The "web" (the part in the middle) is mostly AIR (or OSB) ! The purpose of the web is to prevent the top flange for shrinking/stretching in relationship to the bottom flange.

A large gap in either the top or bottom flange will allow more shrinking/stretching. Additional thickness in the web is uses less.

If you have the C channel, use it. You beam will be much heavier than necessary.

 

[NUTTSGT]

A previous neighbor started to do this in his shop, he ended getting divorced before he finished. He worked for a company called adanmar and they installed conveyor systems. He proposed this to one of their engineers and he told him it would work well within his spec to build a bridge crane across his shop.

Unless you have something crazing huge and a little channel, I can't think of why it wouldn't work

But like Firebrick said, size and span are important.

 

[Joemctag]

Someone w/ more experience than I can probably offer a solution. What I can relate is about weld distortion. I welded two pieces of 8ft angle w/ a 1/2 in flat in between to form a C. It was used to cap the end of a wall. I did a lot of small 1/4-3/8in tacks every 6-8 inches. Got it all tacked and it looked fine. Then went back and made the tacks into 1-1.5in long welds. That thing turned into a noodle. I got on the web to understand the technique of heating a certain spot on a tube to straighten it. Spent WAY more time straightening than the initial welding.

The channels are “symmetric”, unlike angle. Shouldn’t end up bowed , either back-to-back or box-section. Of course, tack-weld first, then alternate final welds. Don’t fully weld up one whole side, then the other, for example. Grind out bevels for the welds if you want. If you’re going to grind the welds smooth ( no need to ), beveling lets you have a nice, good weld. Box section , I’d prime the inside Rustoleum rusty metal primer before assembling . The primer will be burned away at the welds, but it shouldn’t rust too badly up off the ground. If rainwater will get in there, it’ll probably bleed rust forever. You could cap the ends to prevent that. Good luck with it.

 

[charbar]

How big is this C channel? Unless you are planning on parking cars on top of this patio overhang I probably wouldn't be too worried about the strength (assuming it is decent sized C channel and you aren't getting 6 feet of snow sitting on it).

 

[zkdiesel]

I’ve done it. Works great. Take your time. No distortion. I stand under it daily

 

[metalmagpie]

Have a question for you guys. Came across several 12’ pieces of c-channel from a job. This winter would like to work on making a 30’ I-beam out of some of them to be used on a patio overhang.
Would weld the c-channels back to back making an I-beam out of them. I would stagger the joints at 6’ intervals.
Anyone see a big problem with this? Solid weld on top and bottom.
Thanks guy’s appreciate the input

This patio overhang project? You are getting a permit for this work? Because it isn't us you have to get past - it's the structural steel inspector. You obviously don't know how to design weldments - 100% welds is a recipe for unspeakable distortion - so I suggest you hire an architect who knows what he's about. And buy new steel. The cost will be negligible compared to the whole project.

metalmagpie