Width to thickness ratio classification for HSS tubes.

[EngDM]

How do you go about determining the classification of HSS tubes according to CSA S16-14 clause 11.2? There are two different entries in Table 2, one for rectangular hollow sections and one for box sections. The beam selection tables give capacities for the appropriate classification, but how did they determine which set of equations to use to determine class?

Any help or examples is appreciated.

 

[skeletron]

Flip to Figure 2-8 in the Commentary. They have illustrated square/rectangular HSS and the equations for each Class.
Class 1 vs. Class 2 is kind of trivial in most design as you'll be using plastic modulus for bending capacity. Theoretically it could come into play with seismic bracing, which also has its own b/t limits.
Flip through the beam selection tables and note that most sections are b/t x sqrt(Fy) < 425. The ones that are Class 3 and 4 are noted appropriately.

 

[EngDM]

The commentaries of S16-14? All I can find is the full thing.

 

[skeletron]

Get the CISC bluebook. I would reprint it here, but it's probably invaluable if you're designing/learning steel design.