Metal pole/beam/joist definitions and availability

[John Downing]

I am designing a solar carport that utilizes the PV panels as the roof surface. The concept is simple: 4 square posts with aluminum I-beams connecting the easternmost and westernmost pairs, and aluminum C-channel joists spanning between the I-beams. The frame is the mounting grid for the panels.

Other structures I have seen with similar framing members have an angle piece to join the joists to the I-beam. Some are welded, some are bolted. I intend to bolt mine.

Q1) What are these angle pieces called? I have searched several suppliers for aluminum brackets/cleats/angles/whatever and not found any over 3" x 3" x 3"; I'd like to use 6" x 4" x 4". I suppose I could simply buy some aluminum angle stock, cut to length, then drill my own holes.....

Q2) To get the top of the joists flush with the top of the I-beams, is it standard practice to cut back the top flange of the joist so that the web can be moved in closer to the web of the I-beam? Joists will be smaller than the I-beams so the bottom does not need this alteration.

Q3) I have found only aluminum C channel that looks like half of an I-beam, like this: [
I would like to find aluminum joists shaped more like a square tube with 2/3 of one side cut away, like adding serifs to the [ example above. I have seen steel joists formed that way but not aluminum. Is there a specific search term I should use to find such an item?

Q4) To attach the I-beams to the posts, I plan to cut the top and bottom flanges of the I-beams flush with the web of the I-beam, just enough to clear the post, and bolt the I-beam directly to the post. The other side of the flange would be unaffected. Is there any significant loss of strength in the I-beam when the flange is cut out at the end on one side?

Thanks!

 

[driftLimiter]

You are asking a lot here. Are you an engineer who is charged with engineering this structure?

It sounds to me like you need a specialty structural engineer who is familiar with aluminum design.

Remember much of the aluminum structural members that exist are custom proprietary extruded shapes. Because of this, you can get aluminum in just about any shape you want if you are willing to pay for the tooling etc. But it seems like your trying to get away with off the shelf sections which can make things a bit trickier.

Q1) Those angle pieces are called angles lol. Basically a shear tab made with some angle. I think your idea of standard aluminum stock cut to length is the simplest solution.

Q2) The top flange can be coped certainly, but it does effect the strength of the member at the end and will have an impact on the connection strength. Whether or not this is standard practice doesn't negate the need to investigate the strength of the connection.

Q3) Not clear to me what shape you would like, Are you talking like a closed lip channel? Link

Q4) Anyone in the right might mind would need a sketch and loading to comment on this.

Look the connections of aluminum can be the most sensitive (and potentially dangerous) part of a structure like this. It needs someone with experience doing this to properly ensure its strength.

 

[gte447f]

John Downing, are you an engineer charged with designing this structure for a client, or is this a DIY project for yourself? driftLimiter has made some good points already. I would add that, although this sounds like a very lightweight structure, don't let that fool you into complacency. The questions you are asking would be best addressed by a licensed engineer experienced in the design of aluminum structures. Also make sure you have a lateral force resisting system to resist horizontal wind loads, and make sure the structure is adequately anchored to a foundation to resist wind uplift.

 

[John Downing]

Thanks for the replies. I am NOT an licensed engineer; my background is mostly in stick-built residential construction. As suggested, I am trying to build this structure for myself, using off-the-shelf pieces. I am copying in large measure some other structures in my locale that have withstood multiple major hurricanes.

driftLimiter:

A1) "Angles",

A2) I will examine a nearby structure that is using I-beams and Z-channels and see how they addressed this.

A3) "Closed lip channel"? I have never heard the term before. Thanks!

A4) I will attempt to draw my proposed solution and see if that helps. Manana.

gte447f

I have discussed the mounting and anchoring requirements with the local building department. V bracing on two perpendicular sides is part of the plan, and 16" x 16" x 24" underground concrete mounting bases for the corner posts were called "plenty".

Again, I appreciate the information and caveats you both provided. I'm hoping to avoid the expense of a prototype engineered design by relying on locally proven techniques. I hafta know what certain pieces are called in order to look for them.

 

[JLNJ]

Bracing on just two of the four sides is not enough for stability.

If the posts are embedded and considered fixed at the base, then you likely may not need any bracing.

 

[XR250]

I understand your Q4 idea and yes, it should work (for gravity loads). I did that on a deck for my house where I was attaching an I-beam to the side of a Sonotube.