How to interpret section 10.10.3.4 in CSA S6 - Canadian Bridge (Beam bending for class 4 sections)

[Bridge_Man]

Hi All,

I have a two part question about section 10.10.3.4 in CSA S6-14 or S6-19 (pretty much the same)

Assuming I have a class 4 Transversely stiffened web (NO Long. Stiffeners) , and a class 1, 2, or 3 flange. and knowing that I am not designing the section, am just doing an assessment of it so the dimensions and the fact that the section is only transversely stiffened and NOT long. stiffened will not change.

1- Will I be calculating the the flange moment capacity based on its actual class (1, 2 or 3) or will I be assuming the flange is following a class 4 now (since the web is a class 4) , if am dealing with AISC this should not be the case as the flange will follow a different classification criteria (compact/non-compact).

2- assuming that I have the same transversely stiffened girder (NO longitudinal stiffeners) will I have to reduce my moment capacity by the reduction factor in the equation of section 10.10.4.4 regardless of my H/w ratio ? if not what will the difference be whether I have an h/w <150 or > than 150 , please remember that am only providing an assessment of the section not designing.

Am used to the american code not the Canadian code so some of those questions are just interpretation problems.

Thanks in advance

 

[ClearCalcs]

My understanding is that whether h/w is smaller or larger than 150, you consider your flange as class 3 and use the factor to reduce moment capacity. While 10.10.3.4 only directly refers to the factor in 10.10.4.3, the rest of the clause says that moment is calculated using class 3 provisions. The difference between yield and plastic moment comes almost entirely from plastification in the web, which will buckle before yielding by definition for class 4, so it doesn't really make sense to consider the plastic moment as you would in class 1/2.

The difference is that if h/w > 150, you also have additional limits on slenderness for fatigue considerations from Cl 10.10.4.2, which sends you to Cl 10.17.2.5. You may be able to relax the limits for slenderness depending on your utilization in shear at the fatigue load level, which will be affected by your transverse stiffener spacing. If you find your web is exceeding the requirements of Cl 10.10.4.2, a more thorough fatigue assessment is probably warranted.

-Laurent

http://www.clearcalcs.com

 

[Bridge_Man]

Thanks Clearcalcs.

What you said actually makes a lot of sense, I just went back to AISC and that case looks a lot like Case F5

Much appreciated !