Span 7 feet with steel?


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Old 06-15-17, 12:02 PM
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Span 7 feet with steel?

Hard to figure which forum to post this one in? I have an RV with a sagging roof and want to support it from the outside with steel, angle, tubing? I actually want to use aluminum but have read that even 3" X 1/4 aluminum angle will deflect, so that is out.

The steel will go side to side approx 7 feet and will carry little weight, less than 100 lbs. I am not knowledgeable enough to use the deflection calculators online.

The only thing I could find locally that I could test the deflection is 1 1/4x1 1/4X1/16" square steel tubing in a 6' piece. It deflects more than I consider acceptable.

Would any fabricators hazard a guess as what size steel I need. Angle, square, rectangular tubing?
Thanks Jim
 
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Old 06-15-17, 12:25 PM
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I can't help you but I'm guessing those who can would likely benefit if you could post some pictures of this as well.
 
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Old 06-15-17, 12:31 PM
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First, any material will sag or deflect. Steel will provide the most strength for the price. Aluminum can be sized to provide the same strength or stiffness and will be about 30% lighter but more expensive.

I would not worry about the deflection. You likely have rather light weight steel tubing or Z supporting your ceiling now that has a certain amount of deflection even when not sagging.

Tubing would be the stiffest and strongest. A larger size tubing with a thinner wall will give you more strength for the weight but at the expense of more wind resistance and more ugly. A smaller tubing with a thicker wall can be the same strength and provide a lower, more sleek appearance but at the expense of being heavier.

My guess would be to use 1 1/2" 14ga square tubing which will be relatively inexpensive and help avoid adding too much weight to the top of your RV. I just went into the shop and tried a piece of 2" square tubing with 1/8" wall and it hardly deflected under my 160 lbs so I think it's overkill.
 
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Old 06-15-17, 04:53 PM
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A 7' span with only 100 lbs is pretty light duty.

Since it's on the exterior I'd go with aluminum angle or channel, something in the 2x2 size, and then you dont even have to worry about painting.
 
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Old 06-16-17, 12:35 PM
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Many thanks for the responses especially Pilot for going out to the shop and checking.

It dawned on me to go to the local steel place and ask. I went to the sales desk and they said sorry due to liability we are not able to make a recommendation. Go over to the office and ask there.

Went to the office and talked to an engineer, explined what I needed and he said he would use 1X2X 11 gage tubing if he was doing it. Don't know why all of a sudden I am going to trust an engineer?

2, 7 foot pieces of 1X2 11 gauge for $30 and I'm good to go, I suspect it is a bit overkill, but what you gonna do?
Thanks for input, always appreciated Jim
 
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Old 06-16-17, 02:36 PM
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Cool! Rectangular tubing like that is even better than square. A 2" high web of 11ga tubing is overkill but for $30 it's hard to complain. Now you'll be able to carry an elephant on the roof.
 
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Old 06-16-17, 04:57 PM
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Would be interesting to see how you plan on supporting this on the outside of the roof instead of the inside.
 
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Old 06-16-17, 05:48 PM
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Here is a link to one of the projects, the Toyota RV's have limited head room so the outside is preferable and then I can say it is pre framed to mount solar panels instead of a sag repair, if I sell it

Warrior Roof Sag at A/C - Improvement and Do-It-Yourself Projects you have done to Share! - Toyota Motorhome Discussion Board
 
 

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