1/8" wall thicknes on HSS

[Prestressed Guy]

The AISC 13th addition table 4-4 has available strength for HSS columns with 1/8” wall thickness. I have never used less than 3/16”.

I have a situation where because of a series of clerestory windows, I need to place a short lightly loaded 3½” square column under each roof joist at 14’ on-center. I plan on connecting the tops of the columns for collector and chord forces with a C6x8.2 x continuous laid flat over the tops of the columns. Table 4-4 indicates that I am good with 1/8” which would save 50% in materials over 3/16”. Am I missing anything? This project is an SDC D and the columns are not part of the lateral force system but the channel will be a drag strut.

 

[kslee1000]

If you are not convinced, go for 3/16". The saving in material may not worth sleepless nights.

 

[msquared48]

The minimum for welding with one pass is 3/16". 1/8" will be more difficult to weld, but not impossible.

Mike McCann
MMC Engineering

 

[lrhg]

How do the roof joists connect? to the C6? bear on top of HHS 3.5?

 

[Prestressed Guy]

Kslee1000 - I am not overly concerned I just was wondering if anyone had experienced problems with an 1/8" wall column.

Msquared48 - Where do you get the 3/16" min. Table J2.4 lists 1/8" for up to ¼" base material inclusive. I would likely use a 3/16" because the affective throat would be 0.133 which is close to the wall thickness.

Irhg - I have attached a detail showing my connection. It is basically an elongated cap plate that has holes for 2- 5/8"ø threaded weld studs on each side if the column. The channel will have weld studs on the under-side to connect to the column because bolt heads would interfere with the setting of the joist. Splices in the channel would be at the center of the column and the cap plate would provide for continuity and collector transfer.

 

[BAretired]

The only problem I have experienced with material that thin was burn through when welding steel deck to open web steel joists. If the welders know what they are doing, you should be okay. But if you can get by with HSS 3 x 3 x 3/16, the material cost is not too much more and the welding is more foolproof.

BA