AS 4100 5.14.5 1

[rather_be_riding]

Does anyone know if the d term of the equation given in 5.14.5 to refers to the beam depth or the critical flange width?

Furthermore, it seems counter-intuitive to me that as you increase the slenderness ratio of the stiffener, alpha-t approaches zero and therefore the requirement for the Is also approaches zero. I'm sure I'm mis-reading something but it is escaping me at the moment for sure.

 

[Retrograde]

I would take "d" as the beam depth.

I agree that it seems counter-intuitive that as you increase the slenderness ratio of the stiffener Is approaches zero. However the slenderness will be limited by 5.14.2 and 5.14.3.

 

[rather_be_riding]

Retrograde,

Agreed re: 5.14.2 and 5.14.3 - however, it also means in reverse that the chunkier your stiffener is, the larger Is needs to be.

 

[Settingsun]

It does work out. For the requirement to become zero, you'd need an unstiffened web with about d/tw ~110. But that's partially restrained and the clause doesn't apply.

The (minus 0.6) complicates algebraic manipulation, but that part becomes a constant for a given beam and loading. Subtract it out and the remainder is what the stiffener has to deal with. *IF* we ignore the (minus 0.6) just to see the trend, could re-write Le as ~0.9*d, and Is = As*ry^2, and rearrange to get the gist.

Edit: Probably simpler to say that r_y is squared on the left side of the equation but less than linear on the right side, so it converges as the stiffener gets larger, and diverges if you make the stiffener smaller despite how the right-hand-side appears as written in the code.

 

[rather_be_riding]

Thanks steveh49 - I take your point.