Aluminum I beams 2

[eastendeng]

I have a beach front project that requires I beams to support the first floor above and open basement. The floor is residential space over a 4" concrete floor so I'm using 50psf dl and 40psf ll. I've sized it for a w8x15 A36 steel beam. Due to the corrosive atmosphere, steel is not a preferred material. I'm having a hard time finding an adequate resource to determine an equivalent Aluminum I beam. Any suggestions?

 

[JStephen]

There's an Aluminum Design Manual:

http://www.aluminum.org/resources/electrical-faqs-and-handbooks/design

 

[Bagman2524]

Aluminum Structures by Kissell & Ferry is also a good resource. You might want to also consider stainless steel.

Faith is taking the first step even when you can't see the whole staircase. -MLK

 

[jayrod12]

Stainless is more readily available in rolled shapes. At least in my experience.

 

[IRstuff]

The implication is that no steel structures are built by the seaside, which seems counter-intuitive. Surely, there must be ways of protecting steel members, particularly when they are inside a living space.

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[CELinOttawa]

Use patina steel, there are several types. They *are* suitable for interior conditions in a salty environment, but not for fully exposed condition. Steel is very commonly used in NZ with a significant corrosive environment, it just needs to be shop painted, intercoated and top coated, or hot dipped galvanized.

Many engineers do not realize that specifying a beam size up can (though not always) provide sacrificial protection.

Simplest solution: Specify one size up, two coats shop paint, and then intercoat and top coat. Put on the plans that the beam shall be inspected every five years, and painted as necessary and not less than once every ten years as a maintenance item. Job done.

 

[eastendeng]

thanks for the responses and good ideas/references. the area is open in many locations however some is within conditioned space. My first and primary recommendation to the property owner was painted steel (didn't think about up-sizing - good idea CEL). The property owner simply wants to know the cost/configuration of aluminum as an alternative, more as an intellectual curiosity than anything else.

 

[TomDOT]

Hm, from a corrosion perspective I would prefer hot-dip galvanizing to painting.

 

[JStephen]

Using aluminum, especially in small quantities, first thing is to check on availability. It may be more economical to use channels, flat bars, angles, tubes, more members of smaller size, or whatever it takes to match up with what the local service center has available, rather than wide-flange beams. And the alloys easily available may not be the ones you need for corrosion.

I'm not sure how the corrosion compares- I've seen aluminum boats with holes corroded in them, so it's not just completely inert.

Also, I've always heard you're not supposed to have aluminum in contact with concrete for corrosion reasons- typically handled with coatings on the contact surface.

 

[TehMightyEngineer]

RISA-3D will do aluminum design but you really should be using the Aluminum Design Manual.

I've done some all aluminum designs for large drive-in kilns and they can be a pain in the butt to design by hand. Also, welding to aluminum will take out the hardening and makes welded connections an even bigger pain in the butt. Overall, structural aluminum is great and I would love to see people use it more often but it really is just not as efficient as steel, both from an engineering perspective and a cost perspective.

Also, I agree with Tom, hot-dip galvanized would probably be the best bet.

Final note, why did you plan on using a A36 beam in your initial post? A992 is 50 ksi and more readily available these days.

Maine EIT, Civil/Structural.

 

[Jerehmy]

There's an old version of the Aluminum Design Manual online somewhere. It didn't change much at all.

Found it:

https://www.google.com/url?sa=t&rct...IO8944brjYT5-DwUvpPHksQ&bvm=bv.72676100,d.cWc

 

[Jerehmy]

Aluminum rocks, use aluminum

 

[TomDOT]

Aluminum rocks? Do you mean corundum? Aluminum oxynitride? I am unaware of a corundum or aluminum oxynitride design guide for the scale the OP indicated...

 

[TehMightyEngineer]

Jerehmy probably meant bauxite.

But, yes, aluminum does rock and it's a fun little niche to be able to design and use it in your projects. We used it successfully for a moveable safety barrier in an industrial facility. Steel was strong enough but was too heavy for the motor to be used, aluminum was the perfect solution.

Maine EIT, Civil/Structural.

 

[Ron]

I've designed over 600 aluminum structures...for this one, I'd use galvanized steel!

 

[eastendeng]

thanks for the advice/references. for A36 - I initially designed for a992 but looked at a36 just to be conservative. The property owner has already differed to the steel but I'll still look at the aluminum just to see how the members compare and for future reference. I'm all for having as many tools as possible

 

[manstrom]

What about a Wolmanized PSL beam or a treated glulam? These can be stronger than a W8x15 and are much cheaper. Trim it out any way you please.

 

[PEinc]

The A36 steel member usually will still have a minimum yield strength of 50 ksi, probably the same as A992 steel. I just don't see any A36 steel certs showing less than 50 ksi. Therefore, for bending and shear, you may need a bigger beam with A36 instead of A992 even though both are 50 ksi. If deflection is the controlling factor, then the beam size would depend on Moment of Inertia and not on A36 or A992 yield strength.

http://www.PeirceEngineering.com