Proprietary aluminum beam. 3

[awa5114]

I am asked to determine maximum spans for a proprietary solar racking system for which there is no load test data. This happens all too often, and the only engineery information I found is attached below:

This is 6000 series aluminum and I have no experience with aluminum design. I also have a deadline to meet. Using the above information, is there a simple and accurate way to come up with allowable moment capacities? Thanks.

 

[EngineeringEric]

You can analyze it per aluminium design code. just because you have a deadline is not reason enough to not do it correctly, that is life. If you cannot do Al design then why are you doing it on such a short timeline...

The beam can be check for flexural stress and deflection pretty striaght forward but you have to make sure that the extrusion can actually transfer all important loads throughout its section

 

[awa5114]

EngineeringEric.

Thanks for your response. I think for all intents and purposes of this low-risk project we can assume that the extrusion will adequately transfer the important loads.

Now how can I check the flexural stress and deflection ? How straightforward is it? Could you provide a sample calc? Thanks.

 

[Ron]

Agree with EngineeringEric and add the following:

If you are in the US, the Aluminum Design Manual will be the governing code reference.

6000 Series Aluminum is too broad of a categorization. As an example, there are generally 5 or 6 tempers of the aluminum that will give you vastly different tensile and shear strengths. Most structural extrusions are either 6061-T6 or 6063-T6, but they could be T5 on either as well. The tensile strength difference between 6061-T6 and 6063-T6 is considerable. Further, this is an asymetrical section and if you are checking bending, you are likely to get some torsion as well. You'll need to check for this. Lastly, if these sections are to be welded, the allowable stresses for structural aluminum near the weld (within 1 inch) will be greatly reduced by as much as half.

 

[msquared48]

If you cannot get the grade of the aluminum used, specify one in the calculations and cloud it.

6061 T6 and 6063 T6 are very common as Ron noted. Include the spec sheet for the type you use from the Aluminum code in your calculations.

If they want something else, they will have to come back to you, but your but will be covered... as long as you communicate here.

Mike McCann, PE, SE (WA)

 

[mronlinetutor]

u can try using sap2000 to solve it. sap2000 supports aluminum design code. don't think u can verify it by hand because the geometry is complex. the aluminum track must be attached to something and u have to find out the unbrace length. sap2000 is very easy to use:

https://youtu.be/ZKv9VXp-h9g

 

[awa5114]

Would it be possible to simply take the lowest possible yield strength that can be obtained from the various types of 6000 series aluminum and use that? Also I am looking at the Aluminum design manual right now (Section F.2 ) which gives two possible sets of equations utilizing Fy and Sx. The equations are broken down into wrought products and cast products. I am assuming this is a cast product as it appears difficult to work such a complex geometry other than by molding....

If the lowest possible 6000 series yield strength is too low, I could assume something more common. I have seen that 6061-T6 is quite a common one. Please let me know thanks.

 

[Ingenuity]

Call the manufacturer of XR10, IronRidge: Link

 

[EngineeringEric]

and note that the variations in structural capacities in the 6000 are huge... magnitudes different.

I recently did a full hotel rail design and supplier decided to switch grades due to surplus in their field... he wasn't happy when we told them it was garbage to us.

As for allowable stresses, this is based on the mode of failure, and the member being checked. you check the compression flange, the tension flange, the shear elements. the compression elements varry pending on how they are restrained (ie restrained on one side, braced on both, etc). Alum. design manual has examples and very useful tables

 

[NorthCivil]

awa5114

"I am asked to determine maximum spans for a proprietary solar racking system"
you are being asked to provide generic engineering. This is usually bad news waiting to happen in the structural world.

"I have no experience with aluminum design"
read over this one more time.

"Would it be possible to simply take the lowest possible yield strength that can be obtained from the various types of 6000 series aluminum and use that?"
you are not even sure of the grade of aluminum you will be approving.

"Could you provide a sample calc?"
and you want a stranger to do this all for you?

Pardon me if I'm being obtuse, but I'm surprised the folks here have been as helpful as they have been. As somebody with experience in aluminum, it sounds like you and your client should both pause, take a breath, and re-think what is going on. If you keep pressing forward, I think you will be doing yourself, your client, and this whole industry a disservice.

 

[awa5114]

NorthCivil...

You can tell all that to my supervisor. I'm not a PE. I just shut up and execute.

I have to say I completely agree with you though....

 

[awa5114]

@Ingenuity.

I have seen that span table. It's for flush mounted systems. Ours is a tilt-up system

 

[TehMightyEngineer]

Keep in mind that any welding on this will drastically reduce your connection capacities. Aluminum designs are definitely a special animal that's going to take you some time to run the numbers on these sorts of things. I will say that if you've done a fair bit of steel design (light gauge especially) then you can learn aluminum design.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[rb1957]

"I just shut up and execute." ... please don't do that.

worst case scenario ... we help you, you solve this problem, your supervisor thinks "great, he can handle more stuff".

like others, you're asking very basic questions, which in itself is troubling. have you hit the books ? if you had I've thought you could have gleaned more for the data you found and asked a much more directed question, something like "what is the allowable of Al ?" ... even thinking of asking that question should give you ideas on where to look, maybe your supervisor or work-mates ? actually that question should pose "well, how is it failing ? tension or compression ?" the data you have is limited, and so you'll need to make the conservative assumption.

You have determined (I hope) the maximum moment in this rail (for some sort of loading).

If you've done that, then with the data you've given us you should know the maximum stress in the rail.

If you're not there, go to your supervisor and say "I'm out of my depth"; maybe the two of you can go over what you've done already, and move forward.

If you are there, then the question is much simpler "what is the allowable for Al?" I'd've thought that the book giving you the data you first posted, should also include allowables for different grades (it looks likes it's a vendor catelogue).

another day in paradise, or is paradise one day closer ?

 

[Ingenuity]

Contact the manufacturer...

Here is a PE sealed Structural Design Compliance and Allowable Span Certification for IronRidge Tilt Mount Solar Racking System for Flat Roof Applications from their website: Link

They have similar such sealed letters for each state: Link

 

[Ingenuity]

...and here is a copy of the manufacturer's allowable span chart for the XR-10 for wind Cat B with varying snow loads, wind speed, and panel tilt:

Lots of certification data available when you input your state and download.

 

[dvd]

That shape is most likely extruded - link to an extrusion video

 

[DerbyLoco]

I am just working with a railcar shell which will give you some idea of what can be extruded. The wall section is about 3mm min.

 

[BUGGAR]

awwa5114: I get paid a bunch to design aluminum items for the Navy similar to that. I will send you my salary in a private e-mail and if your boss is not paying you that much, I will send a job application to apply to our company. I feel you may be in a career ender right now.