Can you flip an aluminum beam? 1

[S.K.G]

Are you allowed to flip an aluminum beam so that the bottom flange is at the top? I am currently designing a shoring platform that uses 650 aluminum beams. The top flange has a width of 3.5 inches and the bottom has a width of 4.8 inches. The beams have 1.5 inches of plywood on top (2 ply, 0.75 inches thick). The problem right now is that there is too much of a gap between the beams (the clear span) to where the plywood is unsupported for that clean span (currently about 9" clear span). This is a problem because the contractor wants to drive a heavy truck on top and the punching shear would likely be too high from the tire load and cause the plywood to fail. So I am proposing to flip the aluminum beam so that the bottom flange (width 4.8 inches) is on top and thus the clean span between each beam is small enough to allow the plywood to be unsupported only for a small length.
So my question is, are you allowed to flip the aluminum beam? My boss said he has never seen that done before. If so or if not, does anyone know of a reference where it might say it is okay or not okay?

 

[Tomfh]

Turning the beams upside down to “reduce the plywood span” doesn’t sound right. Is this image below what you’re intending? With plywood spanning between beam flanges? This risks bending the beam flanges and/or the beams falling over.

 

[Enable]

For what it's worth I've used aluma beams in the reverse orientation. Details in the following thread:

https://www.eng-tips.com/viewthread.cfm?qid=485703

 

[S.K.G]

@tomfh
yes, that is what I am talking about. Could you elaborate more on the risks of it bending and falling over?

 

[S.K.G]

@enable
I saw your thread and my understanding of it is that it was fine for you to flip the beams as long as you braced the compression flange every 4', am I correct in that? Sorry, I am still new to the field so some of the terms confuse me.

 

[S.K.G]

@IRS
I will talk to my boss about that, thanks for the input!

 

[S.K.G]

@smoulder
what do you mean span to the webs? Are you saying it would be good to insert a piece of wood between the flanges and nail it into the aluma beam web?

 

[Tomfh]

Could you elaborate more on the risks of it bending and falling over?

You are loading the outer edges of the flanges as opposed to spanning to the centre of the beam, meaning you bend the flanges. You are counting on the flanges to make up the shortfall in your plywood span.

and the load is now being applied *outside* of the footprint of the beam, meaning the load from a truck wheel will tend to destabilise the beam.

 

[S.K.G]

@tomfh
yes that makes sense, I will try to see if I can figure out how to check that

 

[Smoulder]

@SKG I'm making the same point as Tomfh. Don't think the flanges can take the load that you want to put on them. But also your plywood is thicker so 250x stiffer cross section than the flanges. Adjust for youngs modulus and the plywood is still 100x stiffer. The flanges probably will bend away and the plywood span full distance between webs anyway.

 

[Tomfh]

SKG - Is this all theoretical anyway? Is the plywood continuous across all the beams? If it is then as Snoulder points out, the plywood will span further anyway.

Personally I would be checking plywood span based on actual beam centres.

How are you calculatin plywood forces? What wheel load? How are you spreading the load? What strip width? And what tyre footprint?

 

[jjl317]

a) Still not sure why flipping the joists would be less re-work then just adding additional joists in between the existing joists (even if the added joists are upside down).

b) In terms of the plywood, it is unclear which design approach you are using. But part of the confusion may be that for the APA (American Plywood Association), some of the design guides considers center to center spacing for bending stress, and clear span for shear stress.

c) I agree with Tomfh that if you do flip over the joists, the top flange stresses under the wheel load condition should be checked, and that the joists need to be restricted from rotating somehow. Important to remember that in the standard orientation, these beams are design to be clipped along the bottom along the slot, which won't be an option upside down.

Good luck

 

[S.K.G]

***Update
Hi everyone,
So I contacted the manufacturer and they said that flipping the beam is not recommended as that is not what it is designed for and they have never tested it that way. Our solution was to add a 0.5-inch thick steel plate on top of the plywood which is much stronger and can handle the extra load from the truck between the clear span. We also dictated a dedicated vehicle travel path under which we added 4 layers of blocking spaced to cover the recommended tire contact area of 20 inches wide by 10 inches long (AASHTO).