HSS with erection holes - Local buckling check using AISC

[SuG89]

Hello,
Please refer to the attached extract from AutoCAD which shows the access holes on a 12"x4" HSS. How can I check the local buckling of this HSS shape at the erection holes for compression and flexure?
Regards,
Su

 

[Agent666]

I assume you are worried about the plate thats left between the long slotted holes?
Why not find out the axial forces at these locations (resolve any axial + flexure in the section as a whole to an axial load in these particular locations), and then simply check it as a very short column that could buckle out of plane. I'd say using an effective length of something like 0.7 x plate length is probably appropriate similar to how you might treat buckling of load bearing stiffeners.

 

[SuG89]

Thanks for your response. I have the same idea but the review engineer doesn't agree with this approach and wants me to check the local buckling of the HSS shape at this location.

 

[Agent666]

You'd check the rest of the section based in it being a C shape for the loads in the rest of the section, you'd evaluate the effective section properties of this C shape based on the outstand to the holes (rest of the section will have the same slenderness as the original HSS, but these newly formed outstands will most likely be compact.

Once you have the properties just evaluate the strength of the C like you normally would, also check the bit between the holes as a short column as previously noted.

 

[SuG89]

And you suggest to use K=0.7 (pinned-fixed).
Would it be overly conservative to use K=1.0 (pinned-pinned)?

 

[Agent666]

If it works then no issue, I believe it would be conservative, not overly so.

Not 100% familiar with AISC, but my own local code for Stiffener Design uses 0.7 effective length factor if the stiffener is welded and rotation is constrained. Perhaps something similar exists in AISC to justify your design checks.

 

[SuG89]

Thanks once again!
Regards,
Su

 

[SuG89]

For the C shape, would it be ok to resolve the axial compression and flexure in the section as a whole to an axial compression load and then check for buckling?

 

[Agent666]

Assuming at the point where the holes are you have a global axial and moment forces acting on the cross section, then the C shape over the length of the holes simply sees the loads occurring in only the C due to these loads. It won't be a purely axial force. For example consider the stresses across the section as its easier to visualise, they won't be uniform, they will instead vary due to the presence of any moment.

Don't forget to also check the global buckling of the entire length, some codes require you to use the net area of the section (gross section reduced by the area of the holes) to check the section capacity and axial buckling of the entire member.

 

[Agent666]

New Zealand and Australian steel codes require the net area to be used for global compression checks except when the area deducted by penetrations or unfilled holes is less than a certain percentage of the gross area(being 100 {1 – [fy / (0.85fu)]}%)

Whereas other codes such as Eurocode specifically note that the net area doesn't require consideration for compression checks.

AISC only notes the gross area, and there is no mention at all of the net area in the compression rules.

Edit, I see the previous poster deleted their question about what codes used the net area as I was typing my reply!