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cherm90 07-27-2012 06:09 PM

Steel I beam size
Will a 6" steel I beam sopport a 20' span on a 20 x 14 deck attached to the home on one 20' side

GBrackins 07-27-2012 06:27 PM

why would you use steel that is exposed to the weather when treated wood may be a better option?

ben's plumbing 07-27-2012 06:58 PM

agree why would use a steel beam out in weather.....:eek: just a question for this old mind..:yes:

cherm90 07-27-2012 07:24 PM

I already have the steel I beam, and how can I span 20' with wood? I cannot have a center post because it is going to be used as a carport underneith. My wife would hit the post the first day.

user1007 07-27-2012 08:33 PM

Exterior rated glue lam!

Daniel Holzman 07-27-2012 08:44 PM

The words "6 inch I beam" do not define the beam. There are numerous steel beams that are approximately 6 inches deep, with widely varying properties. There are two different S shapes that are 6 inches deep, and 4 W shapes that are nominal 6 inches deep. Not to mention that steel comes in strength ranging from 30 ksi to over 120 ksi. Basically you are asking folks on an internet chat forum to tell you if an undefined steel shape, with unknown properties, is capable of supporting a partially defined load. Suppose someone is tries to answer your question. What are you going to do with the answer?

GBrackins 07-27-2012 09:21 PM

you could use a preservative treated parallam wood beam ....

Joe Carola 07-27-2012 11:52 PM

They make exterior steel I-beams.

Joe Carola 07-27-2012 11:53 PM


Originally Posted by Joe Carola
They make exterior steel I-beams.

Company called "Better Header" sells them.

tony.g 07-28-2012 02:22 AM

Without knowing details of the beam and required loadings, it is not possible to determine if it will be satisfactory in bending, buckling or deflection.
Assuming it was OK, the OP could potentially have some other problems, apart from a wife who can't drive.
For example, how would the beam be fixed to the posts? There would almost certainly be some eccentricity in the fixing, which will induce a bending moment in the posts.
Hopefully the posts are not 4x4 timber and are not too long.

cherm90 07-28-2012 07:30 AM

I guess steel is just not my thing. I have never had to try to use it. The beam is from the main frame of a mobile home that I scrapped. It is 6" tall, 31/2 " wide, and the 6" main I is 1/2 " thick. the top and bottom 31/2" is just under 1/2". I don't know if any of this helps. It was a beam I have and thought it may possible work. If not, I will just re-design my plan.

tony.g 07-28-2012 09:52 AM

Cherm; Am not familiar with US beam section-sizes and properties. However, here we have a beam 152 high x 89 wide, which is very similar to your 6" beam, though the flanges and web are slightly thinner (about 3/8").
Assuming a live load of 40lbs/sq ft (which I think your code would stipulate), I did a quick check and there is no way that beam would be able to span 20' without being overstressed. Also, I don't know if your code gives limits for deflection for deck beams, but this steel would deflect considerably; the deck would probably have too much bounce.
Personally, I'd forget the steel, and use timber instead.

Daniel Holzman 07-28-2012 11:55 AM

Your beam has the approximate properties of an S6x17.25.
The exact properties of an S6x17.25 are as follows:

Height 6.00 inches
Width of flange 3.565 inches
Thickness of flange 0.359 inches
Thickness of web 0.465 inches

If you do have an S6x17.25, it is most likely A36 steel, which has an allowable yield stress of 24,000 psi. There is a chance you have A60 steel, which has a higher yield stress. If you are lucky, the beam may be stamped with the strength, and possibly the manufacturer.

The moment of inertia of an S6x17.25 is 26.3 in^4.

If you can confirm the dimensions, that would give you all the information you need to compute the strength of the beam, and the deflection.

tony.g 07-28-2012 04:53 PM

2 Attachment(s)
Daniel; re your data on the OP's steel beam. Having nothing better to do, did some rough figures for the loads.(attached)
If the top flange was fully restrained (so that it could achieve maximum stress) I reckon he could just about do it @ 40 psf live.
But - can't see how he could effectively restrain the top flange, and allowable stress would probably be about one-half maximum, hence fail.
Either way, deflection under live load might be excessive - but then I don't know what they allow for decks.
OP's probably better off going for a stout timber beam. (Even better with a post in the middle, if he could get his wife to aim the car at the gaps).

robertcdf 07-29-2012 04:59 PM

I'd use steel (and do everyday for deck beams) but I'd leave the speccing of the right size to my engineer, that's what I pay him for.

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