HSS T connection 1

[JT-1995]

I have a simple T connection of two HSS12x8x3/8's. I am interested in making a clear hand calc, followed by a spreadsheet as I expect this connection will happen often in the future. A few parameters that are in my mind:
- this connection will be all welded.
- there will be field weld applications and shop weld applications. For the field weld a 4" long 4x4 angle "t" distance below top of steel that will slip inside the top of the beam HSS and the erector can use it to seat the beam while it is welded.
- The side walls of the beam will weld to the girder with fillet welds. There will be Flare Bevel welds at the top and bottom to negotiate the radius on the girder.
- There may be times when the beam does not match the depth of the girder, so the bottom weld will be a fillet weld and there will be an additional place to check local stresses.
- If tolerances of on site conditions are a concern, angles may be welded to the web of the girder and the beam slid between them and then welds made between the angle legs and the beam webs. This can allow the beam to be a little short and the connection will still be made. This is a little different calculation, but a simple variant if the full weld design can be mastered.
- Moments do not have to be transferred at the joint, but the frame design has considered both moment connections and pin connections and all members are fine in all conditions. The thought was to now design the connection welded all around (to keep water and debris from getting inside the tube) and make sure all cases of joint fixity are covered from a capacity standpoint.

So being unfamiliar with the nuances of these connections I have studied AISC 360-22 Section J and K. They are a bit cumbersome and I hoped for some clarity from this group. I also spent a little time on the Steel Tube Institute web page, and a little time with Blodgett.

[ol 1]
[li]Can someone clarify, is AISC 360 Section J intended to focus on simple connected joints?[/li]
[li]Is Section J focused on Wide Flange members or are the formulas valid for closed sections too? There are some notes in the text of AISC 360 that seem to indicate the formulas are valid for HSS but with some "additional requirements" in section K.[/li]
[li]Does anyone know a great resource to see worked examples of these calculations for a such a simple connection, in order to see the formulas in Section J and K in action?[/li]
[/ol]

Thank you for reading.

 

[dauwerda]

https://www.eng-tips.com/viewthread.cfm?qid=506350[/URL]]In regard to the tables in Section K of AISC360 (specifically K3.2 in 360-10 or K4.2 in 360-22) the formulas seem to be derived for a vertically oriented branch. Examining that closer, it appears the branch is connected to the width (B) of the chord and the moment load is oriented bending in what we may call the "weak" direction. I believe this is all because these codes started development because of HSS TRUSS designs not horizontal beam designs...maybe.

So if you agree with any of the above, if I am designing a T connection of a horizontal HSSS12x8x3/8 branch beam Teeing into the 12" face of a horizontal HSS12x8x3/8 chord beam. So to determine the flexural strength I need to flip flop all of the H and B variables. Does that seem right?

The tables don't care so much the actual orientation of each member (vertical or horizontal), what is important is the relationship of the two members to each other and the direction of the loads/moments (in-plane, out-of-plane, etc). The variables (B, H, etc) should always match the actual geometry. That is, "H" doesn't care if it is the 12" side or 4" side of your beam, "H" is going to be whatever side of the beam matches the picture. It sounds like you are describing what I have shown below, with image rotated 90° on the left. If your girder is oriented in the "strong" direction such that it is 12" tall and 8" wide, "B" is 12" and "H" is 8". If it is oriented in the "weak" direction such that it is 8" tall and 12" wide, "B" is 8" and "H" is 12"

Per your questions in the above post, up through AISC 360-10, HSS connections were exclusively covered in chapter K. In AISC 360-16 chapter K was completely reorganized and chopped down because many of the required checks were required in chapter J, and the committee did not want to have multiple locations with the same information. So yes, J is definitely applicable to HSS and yes, K provides addition requirements/information specific to HSS.
When 360-16 was first released, the steel tube institute put together tables to show designers where to find the checks that had all previously been in chapter K, that can be found here:

https://steeltubeinstitute.org/product/aisc-360-16-limit-state-tables/

 

[JT-1995]

Thank you again dauwerda. Yes your rotated image is what I am designing. I think we land at the same place, I appreciate you taking your time to describe the orientation.

Also, thanks for connecting the two posts. I had the STI limit state tables but had not found them helpful. This morning I looked at them with fresh eyes and I see their value now for my design in the last table.

Cheers.

 

[dik]

Just a caution, some of the tables have a 'range of applicability for the HSS properties.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik