Round HSS Local Yielding

[hitch22]

Hello fellow engineers,

I have a structural problem involving a round HSS which I hope you may help me with. This is the situation.

1. There is an HSS406x9.5 column which will receive moment from a W310x97 as well as an axial load. The factored moment is 229 kN·m and the axial load is 33 kN in compression.
2. I treated the beam flanges as transverse plates. According to my calculations the capacity of the HSS406x9.5 is 389 kN but the factored load in the compression “transverse plate” is 816 kN. Therefore, the HSS will fail under local yielding.
3. The HSS406x9.5 columns and the W310x97 beams have already been purchased and so I can’t use different sections.
4. Since the wall of the HSS406x9.5 is too thin I was asked to calculate the thickness of a doubler plate to resist local yielding. According to my calculations, the total required thickness (HSS wall+doubler plate) is 13.8 mm. Therefore, I need 4.3 mm (13.8mm-9.5mm) more. I recommend adding a 9.5 mm thick doubler plate.

My question is:
Will doubler plate and the wall of the HSS406x9.5 act together so that it’s ok to simply add a 9.5 mm thick doubler plate? I based my calculations on Table K1.1 (Transverse Plate T-and Cross-Connections) of the “Specification for Structural Steel Buildings”.

Any help would be greatly appreciated.

 

[Lomarandil]

A sketch of your connection detail would help, but if I'm understanding you correctly, the doubler plate will not act compositely with the HSS wall (presuming you weld around the perimeter or similar).

You can probably provide a 13-14mm doubler plate to carry all or nearly all of the local stresses. But since stresses are non-linear with thickness (think about the section modulus of a 1"x12" plate compared to a 1/2"x12" plate), your required thickness isn't just additive.

 

[hitch22]

Thanks for the reply Lomarandi. I attached a link to a sketch of the connection in the original message, but I think you understood regardless.

 

[BUGGAR]

In the utility industry where we have connections like this to monopoles, we frequently weld thru-members in the pole to spread the load. Look up at the cross arms on your nearest utility monopole. We typically moment-bolt the arms but they could be welded.

 

[Lomarandil]

Sorry hitch! I scrolled right past it.

Yes, based on that geometry I'd have a hard time justifying the two plates working together.

 

[hitch22]

Buggar,

I thought about running a plate through the HSS, but I thought that would be more expensive than using a double plate.

 

[KootK]

It surely would be more expensive. But then it might be the difference between a detail that works and one that doesn't. Another consideration with the doubler plate is the stiffness of the moment connection.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.