Aluminum Zee Stand in Compression & Bending

[DDDeng]

I have a situation where a cold bent aluminum Z member is utilized as stand and want to determine its capacity. The Z shape is 1/8" thick aluminum plate with a 2" bottom horizontal flange, 7" tall vertical web & 2" top horizontal flange. All bends are 90 degrees with a radius of about 1/8". The Z shape is 8" long. The 2" bottom horizontal is bolted to structure below. Top is rotation fixed and translation free. There is vertical load putting the 7" tall web in compression and due to the 1/8" thickness potentially a buckling concern. There is also a horizontal load applied to the top flange. I am considering the impacts of pdelta for this situation.

Finding the capacity in bending and compression is simple if ignoring the effects of the rounded corners. I have limited experience in working with cold bent shapes and am looking for some direction/guidance on approach and impacts of the rounded cold bent corners.

Thanks in advance!

 

[jjl317]

My first thought would be what alloy/temper are you planning on using? Some are relatively easy to form (i.e. 3003-H14) but not as strong while others are difficult and prone to cracking (i.e. 6061-T6) but stronger. You may want to talk to a fabricator familiar with forming aluminum.

For 3003-H14, which I have used on many architectural panel jobs, I never considered a reduction in strength due to forming, and in some cases, it might be possible to consider an increase due to cold working (will be interested to see if anyone here will confirm or oppose this thought)??.

While there are certainly a number of unknown variables for this application, I might look at bolting together two LLV 6061-T6 angles, which could eliminate the rounded corners, and allow for the use of a stronger alloy/temper.

 

[rb1957]

yes material properties are one thing.

analyzing a formed section ...
1) including the corners is a bit of a PITA, but not so much these days.
2) you could use CAD for section properties,
3) I do a lot of hand calcs and simplify to ...
a) extend the flanges into the corner (make the formed radius a tight zero radius corner) and omit the overlap square in the corner (clear as mud ?)
b) extend the flanges to the mid-thickness (and agonize over the overlap)