F13 of AISC360

[EngDM]

Hey all,

I came across a clause in AISC360 that I don't believe is covered in CSA S16, and I'm wondering if I am interpreting this correctly.

Equation F13-1 reduces your moment strength by way of two components when you have holes in your tension flange; using Sx in the equation and by taking the ratio of net flange area to gross flange area. For cantilever beams supporting OWSJ's, there have been times where I've seen the joist heel be a bolted connection to the top flange. Does this mean that any beam that was sized using Zx (plastic modulus) for strength and is loaded above the elastic capacity (Sx) just never passes this clause?

Again this is only for bolted top connections for cantilevers where it runs above a column and the top flange is in tension. Whenever it's welded this isn't a problem.

It also introduces a problem that you cannot use a bolted flange plate splice to develop the full capacity of the Class 1/2 beam. Since you are immediately limited to Sx and use the net area due to bolt holes, the difference in using Fu instead of Fy in the equation just isn't enough to meet the original capacity, assuming we are using typical Gr. 50 material. This is an issue with those "design connection to full member strength" that we all know and love.

 

[JoshPlumSE]

This is just the equation to check "tension rupture" of the flange, right?

I have to believe that the CSA code has that in it as well. Have you looked at clause 13.2(a)(iii)?

Note: I don't have a copy of the CSA code anymore, so I'm just going off a citation for a program that I helped develop. Where we checked tension rupture using the following formula:

Tr = Phi_u*Ane*Fu​

​

Tr = Design Capacity of the flange​

Phi_u = strength reduction factor for rupture​

Ane = effective net area of the flange​

Fu = Rupture stress of the material.​

And, we check that against the tension demand from moment and axial force in the member.

 

[EngDM]

This is just the equation to check "tension rupture" of the flange, right?

I have to believe that the CSA code has that in it as well. Have you looked at clause 13.2(a)(iii)?

Note: I don't have a copy of the CSA code anymore, so I'm just going off a citation for a program that I helped develop. Where we checked tension rupture using the following formula:

Tr = Phi_u*Ane*Fu​

​

Tr = Design Capacity of the flange​

Phi_u = strength reduction factor for rupture​

Ane = effective net area of the flange​

Fu = Rupture stress of the material.​

And, we check that against the tension demand from moment and axial force in the member.

The CSA clause you've put above seems correct (although I wish they would present the equation in a separate flange-force equation), but the AISC code directly uses Sx and makes it a moment check instead of it just being a simple tension check.

Where CSA just checks Phi*Fu*Ane for a Tr which you can compare to your demand/depth Tf/Cf forces, AISC is checking Fu*(Anet/Agross)*Sx and reporting an Mn. The former doesn't pigeonhole you into treating all shapes as Class 3.