HSS with holes 1

[vmirat]

I'm designing a steel framed canopy with HSS 10x10x1/4 columns. The architect wants electrical recepticles recessed into the columns, so the column will have a 4"x4" square hole in one side. I've never come across this situation. I've always seen stuff surface mounted.
What is the failure mode of this column at such a large hole?

 

[vmirat]

Oops. Forgot to mention that the columns are designed as inverted pendulums (moment connection at foundation) with the canopy as a pinned connection at top.

 

[hokie66]

Should be doable from a stress standpoint. Just check the stresses at the point of the hole. Hopefully, he doesn't want the holes right near the bottom.

A bigger concern, as these are external columns, would be corrosion. I would want them to be hot dipped galvanized to protect the inside of the columns.

 

[vmirat]

I did a check on bending stress by calculating the moment of inertia of the revised section and it was OK. I was wondering if there will be substantial stress concentrations at the hole corners or if buckling of the hole edges due to compression would be a problem, or any other condition that I'm not thinking of.

All structural steel is supposed to be powder coated after fabrication (i.e. after the holes are cut). What is it with architects and powder coating anyway? They love this stuff.

 

[hokie66]

I would insist on the hole corners being rounded. Drill the corners and cut out between.

Powder coating will not protect the steel, particularly inside. Galvanize it first, then powder coat. However, the galvanizing may not give a smooth enough finish for the architect, but then some like it rough. You can never second guess an architect.

 

[vmirat]

You hokies are so bad!

I thought about having them drill 1/4" holes at the corners. Thanks for validating that.

 

[Ron]

hokie66 is exactly right. Agree. Have done hundreds of these in aluminum...same considerations.

 

[ToadJones]

I'd make the holes in the corners bigger than a 1/8" radius...I'd go more like 3/8" or 1/2"

 

[shobroco]

Most sign pylons & light poles and plenty of gas station canopies have this type of hole in them. Take a 1" long slice of 4X4X.25 HSS & weld it inside the opening to reinforce it. Ot has nicely radiused corners and it can sit completely inside the column or project out 1/4" to provide a good place for a gasket on the electrical cover to seal.