Questions for Experienced Fabricators

[Bucksaw]

So, I have been toying with the idea of building a flatbed for my pickup for a couple different reasons. I think I have the plan figured out, but I need some input as to materials to use. Most commercially produced flatbeds on the market are constructed using 4" channel iron, which has about a 1/4" thickness, for the main runners that bolt to the frame and tie the receiver hitch in. This 4" channel takes the brunt of the force applied by the receiver hitch, which are usually rated for around 15K, and the gooseneck hitch, which is rated for 25-30K.

My question is, would it be incorrect to think that I could use 2"x4"x1/8" rectangular tubing to build one without running the risk of catastrophic failure? My pickup has a factory gooseneck setup, so the bed would be tied into the gooseneck hitch for mounting support for the bed, but wouldn't have to support any weight being applied to the gooseneck ball. It would, however, be tied into a replacement receiver hitch setup, and would need to be strong enough to pull at least 7K safely , probably closer to 10K to be on the safe side.

We have built trailer frames for BBQ pits pushing 4500 lbs out of this tubing before with good results, and in my mind it is just as strong as 4", 1/4" thick channel iron because it has two 1/8" sides as opposed to the single 1/4" side. 1/8"+1/8"=1/4", so therefore I would think that the rectangular tubing is as strong because it is the same amount of metal, just configured a little differently. However, I am also aware that that difference in configuration can mean entirely different engineering characteristics. Im just not enough of an engineer to make that determination.

Can someone who knows for sure tell me if using the rectangular tubing will be strong enough?

[Bucksaw]

Also, not to sound like an unappreciative ****, but while I can appreciate those who follow the mentality of, "when is doubt, overbuild it," (myself falling into that category) I have reasons for wanting to use the tubing if it is deemed to be a safe alternative, so please don't suggest that I use channel just because. I am looking for an education, not an assumptive opinion. Thanks.

[Dale Moser]

I think you'll love the way that tubing works out, I wouldn't hesitate to use it in place of 4" channel for that application.


Channel is a pain in the *** to work with anyway.

[SB09]

On 4'' channel I show the flange thickness to be 5/16 in both the 5.4 and 7.25 weight per foot configurations.

I think you'd be just as strong or stronger. But, I'm no engineer, so don't take that as right.

[Bucksaw]

Channel is a pain in the *** to work with anyway.

That's primarily why I want to use the tubing.

[bboswell]

Provided you are standing the rectangle tube up so it is 4" tall it will be slightly stronger than the channel with the same total section area.

[Bucksaw]

Provided you are standing the rectangle tube up so it is 4" tall it will be slightly stronger than the channel with the same total section area.

Yes, it will be stood so that it is 4" tall and 2" wide.

I figured it would at least be as strong as the truck frame, considering that's basically what the frame is made of.

[Dale Moser]

Go for it, and miter those corners so it looks nice and slick!

[SB09]

I talked with everyone here at the office about it. Over 100 years of structural steel experience. They all say it will be stronger than the channel.

[bboswell]

Only thing you lose is the ability to hook a ratchet strap to the frame to tie stuff

[fullsizeaggie]

I built 2 that were rectangle frame on 4 sides with the internals or cross bracing being channel. Just welded the ball mount in between 2 channel braces and then added bracing to "spread out" the load. Used 2" 1/4" wall on top of truck frame and then built up from there. Never thought out using all box - woulda been quicker. Just did what I was told.

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[Bucksaw]

After reading the comments so far, I began to wonder why manufacturers use channel. Only thing I can figure is that it is more cost effective. I got prices this morning and there is about a $.15/ft difference. I guess if you are building thousands of them each year, $.15/ft adds up.

[bboswell]

After reading the comments so far, I began to wonder why manufacturers use channel. Only thing I can figure is that it is more cost effective. I got prices this morning and there is about a $.15/ft difference. I guess if you are building thousands of them each year, $.15/ft adds up.

Channel can be sheared instead of saw cut which makes it faster as well

[Bucksaw]

So what about 2x2 for the cross braces under the floor? I'm trying to keep the floor height as short as possible because the truck is already so tall. Standard braces are 3" channel. Would the 2x2 hold up good enough?

I know it's only an inch, but an inch is a long way when jacking up a loaded gooseneck trailer.

[Dale Moser]

So what about 2x2 for the cross braces under the floor? I'm trying to keep the floor height as short as possible because the truck is already so tall. Standard braces are 3" channel. Would the 2x2 hold up good enough?

I know it's only an inch, but an inch is a long way when jacking up a loaded gooseneck trailer.

I wouldn't.