HSS Column Chord wall plastification 3

[AvinashVeeresha]

While checking the moment connection for a W beam to HSS16x16x5/8 column we found out that the wall of the HSS column fails due to plastification. Can we spec a internal diaphragm plate as thick as the W beam connecting and get away with it.The arch wast to use the HSS for aesthetics and the utilization ratio of the column in 0.93 so we cant reduce the width of the column.

Is there any calculation that needs to be done to check the internal diaphragm plate ?

 

[JoshPlumSE]

How can you create an internal diaphragm plate? How does the welder get inside on both sides of that plate?

There are cases like this where you interrupt the column with a stub piece that has a plate on both sided. In those cases, the plates are continuous and the HSS column gets interrupted.

 

[jayrod12]

I've tended to see a WT used as the shear plate in these instances as the flange of the WT is usually thicker than the HSS wall. You could just provide a plate welded to the column that is thick enough to span between sidewalls. I think diaphragm plates are going to be a fabrication nightmare.

 

[JoshPlumSE]

This is the connection I was thinking about. From the AISC Design Guide 24 on HSS connection. This Design Guide, by the way, is a must have if you are going to do a lot of HSS.

There are variations of this, of course. And, Jayrod's idea is a fine one as well... if the moment isn't too large.

 

[r13]

Just a random think, will a vertical extended end plate weld to the column work (if column is wider than beam)?

 

[DrZoidberWoop]

You can disperse the flange force load causing HSS wall distortion by using one of the connections recommended in chapter 12 of the AISC Steel Construction Manual (pg 12-25&26 in 14th edition and pg 12-27&28 in 15th edition). If you really want to go with an internal diaphragm plate, your fabricator may give you pushback because it's the least economical/most costly option (because of the CJP with backing required to repair the HSS). I would only go with the internal diaphragm if the connection reinforcement can be fabricated entirely in the shop and the architect had rejected all other options.

 

[JoshPlumSE]

DrZ -

Yes, those connections should be much more economical. The one I proposed may only make economic sense for very high moments or seismic cases where you're trying to develop probably plastic moment.

 

[DrZoidberWoop]

JP - Your recommendation would work out fine. I've used all of the connections cited, except for the internal diaphragm, which I avoid like the plague. I've had to observe NDT of field-welded CJPs, with backing, in HSS before and it's way more trouble than its worth.

 

[KootK]

I dunno, I kinda like OP's detail if the joint is exposed and needs to look pretty. It seems to me that:

1) Most of the troublesome welds would be done in the shop and;

2) He's thought of the diaphragm weld access thing by having the HSS fabricated in two pieces and welded together after the diaphragms get installed.

3) It might be easier to hold the diaphragm plates in place during welding if the diaphragms were not full depth.

Is there any calculation that needs to be done to check the internal diaphragm plate ?

4) The diaphragm plates must not be allowed to compression buckle.

5) This might be easier to do with diaphragm welds as something other than full penetration welds. Whatever you do, make sure that it can move the diaphragm shears into the HSS side walls.

5) You still need to check shear, and shear buckling, of the HSS walls in between the diaphragms.

 

[AvinashVeeresha]

Thank you for all your valuable response, unfortunately we have moment connection all four sides and chord wall plastification is an issue on all four sides ( we had to rule out thru plate and External diaphragm plate). Can we suggest a cladding to the HSS?, in that case will the thickness of the cladding alone should satisfy chord wall plastification requirement or should the combined thickness of HSS wall + Cladding satisfy chord wall plastification.

I will do these checks and this is helpful

 

[DrZoidberWoop]

It is your design, and you can do as you wish, but instead of pushing the HSS column to its limits and adding reinforcement, I'd either increase the HSS thickness or specify a box column made from grade-50 plate that can handle the loads. Anything to minimize labor costs and save you valuable time.

 

[KootK]

@Avinash:. What document did those details come from?

 

[phamENG]

Latest post is straight out of the SCM. It's not the 14th edition (all figures of off by one but the content matches my page 12-27 exactly), so it's either the 13th or 15th.

 

[AvinashVeeresha]

Its from 13th edition steel construction manual.

 

[KootK]

Thanks guys. The topmost of those four reinforcement details seems like a strange way to reinforce.

Can we suggest a cladding to the HSS?, in that case will the thickness of the cladding alone should satisfy chord wall plastification requirement or should the combined thickness of HSS wall + Cladding satisfy chord wall plastification.

You might combine resistances for compression load delivery but not for tension load delivery unless you took deliberate measures to ensure that the cladding and HSS wall were adequately connected such that when you pulled on the cladding you'd also pull on the HSS wall.

 

[phamENG]

KootK - seems that would be a benefit of the topmost detail, wouldn't it? If the reinforcing angles are welded along the center line of the HSS wall, then the tension force is transferred through the cladding to the HSS wall at that weld.

 

[KootK]

Still seems to me that the angle legs don't actually span across the HSS face that you're trying to prevent classification in. I'm sure it does something and, sized right, could do enough. I'd not look forward to trying to sort the numbers though.