HSS bracing

[Leenew]

I have seen so many HSS braced structures that use a shear plate (inserting the slot) to insert in the center of HSS member and use two more extra little plates to cover the open areas. It is a lot of work to do. Why don't they use an end plate and stem?
I have been puzzled for a while about this.
I need to design a bracing using HSS5X5X0.25 and HSS5.5X5.5X0.25.
Any suggestions?

 

[ARKeng]

I suspect with the end plate/stem design might relate to concerns over evaluating the bending of the end plate, especially for local stress concentrations. Most of the other designs you allude to have a more direct load path / uniform sharing of stress that's easy to calculate by hand.

 

[Mjkkb2]

Slotted hss connection is a very common detail here on the East cost. One thing to add to the above is allowance for adjustability in the field which end plate does not provide. I typically spec slotted brace connecting to a gusset with fillet welds each side along the slot. Quick, cheap and easy to install.

 

[Leenew]

Thanks both for the input!
Mjkkb2, what do you mean the adjustability? The stem plate can do the same, right?

 

[racookpe1978]

The slotted "tab" in a tube steel connection acts also to tie together the two opposite walls of the TS. (HSS).

 

[Lomarandil]

Leenew -- if a slotted HSS length is a little bit off, that's no issue. Just have a little more or less gusset plate in the slot. If an end plate HSS length is off -- that can be tough to adjust.

----
The name is a long story -- just call me Lo.

 

[Mjkkb2]

Lo is correct, the slot is typically provided an inch or so longer than the length of weld required so if some sliding of brace must be done you still end up with the design weld length...

OP - I am not sure what you mean by stem plate?

 

[SteelPE]

Yes, eccentricity is a killer in that end plate/stem plate connection. Try driving 60 kips through a plate where the eccentricity causes weak axis bending.

 

[CANPRO]

Maybe leenew can clarify, but I interpreted this to be a plate that is slotted and shop welded to the HSS and then bolted to a gusset on site. In which case the adjustability and eccentricity issues are the same for slotted plate and end plate + tab.

EDIT: To answer you question - assuming you're talking about all shop welded plates and site-bolted connections - if you slot in a plate, the extra little plates on the sides are just to seal the ends...probably 3/16" plate with seal welds, fairly quick and easy (and some cases maybe not even required). With the end plate + shear tab, now you have a structural weld between the end plate and HSS and again between the tab and the end plate, and the end plate will have to be thicker as well.

Regarding the analysis of the end plate + tab plate option - this is covered in AISC Design Guide 24.

 

[Tomfh]

Slotted plate is stronger.

With an end plate + stem plate there is stress concentratration where the stem meets the tube walls. The plate isn't generally thick enough to transfer the stem loads into the tube. This concentrates the load over a short section of weld, allowing weld unzipping to occur.

If you have a very thick end plate the loads can disperse into the tube, but mostly people don't have very think end plates.