Is this a moment connection? 1

[AlexWong122]

Hi Guys,

This is a moment frame structure I want to use in combine with wood panel shear wall in a single family house, due to the reason that there is not many interior wall at that location. I have used Sap2000 to model this moment frame, and it appears that it gives very similar deflection as my wood shear walls under the same load (my design load is around 12 kips for this moment frame). In the model I assumed fixed connections and I just want to confirm that my connection detail will work.

Due to the limited space, I am only welding the column to the base plate with 9/16" fillet weld. The nuts and washers are not welded. The column height is 10' and the span is 16'.

Thanks,

Alex

 

[hokie66]

It has some stiffness. You would have to determine how much by assessing the capacity of the HSS, base plate, welds, anchor bolts, and concrete pier. Because you show the anchor bolts as just straight bars, I imagine their capacity or that of the pier will control. Even if strong enough, there will be some flexibility. So in summary, it will take some moment, but it is not fixed.

 

[TehMightyEngineer]

Agreed with Hokie. However, no connection is truly fixed or pinned. In my mind the baseplate is the most flexible thing here; if you're stiff enough to avoid significant deformation or yielding of the plate then you'll likely be stiff enough to consider this fixed. Lower-bound theorem and all that. Just make sure your anchor bolts do not control and you should have a ductile system where as long as all your limit states are good you can consider it a moment connection.

Design Guide 1 from ASIC and Hilti or Powers anchor bolt software are your friend.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Lomarandil]

Agreed with the above.

But why are you welding your nuts?

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

 

[KootK]

My take:

1) Without doubt, its a connection capable of transferring some moment. And it will until something yields or fails.

2) I my opinion, whether or not something is a moment connection has as much to do with the connected element's lateral stiffness relative to other parts of the structure than it does the details of the connection itself. If this column exists in a moment frame building, plan for this joint to see some moment. If this column exists in a building braced by concentric bracing or shear walls, consider designating the joint as pinned.

3) Based on the proportions that you're showing, I'd speculate that your capacity will be limited by shear breakout of the concrete surrounding your anchor bolts.

Is this a moment connection?

Is this a situation where you want this to be a moment connection? Is it part of your designated lateral system? Or are you wanting to call the base fixed for the purpose of determining your buckling effective length?

But why are you welding your nuts?

The intent may be to weld the washers so as to be able to transfer shear without giving up the tolerances provided by oversized holes.

 

[AlexWong122]

Thanks all for your inputs and seems my previous sketch has made some misunderstanding. I have updated the sketch and add some more details to the problem to for your information.

Alex

 

[KootK]

Okay, so you want this to be a moment connection then? It's part of a designated moment frame?

This paper by Widianto is popular for designing your connection to do what you need it to: Link

 

[CANPRO]

Alex, I see a few problems with this detail:

[ul]
[li]A 9/16" fillet is a fairly hefty weld considering the size of this frame. And it doesn't match up with the 9/16" baseplate or the 5/8" anchors. Either the baseplate/anchors are undersized or the weld is oversized.[/li]
[li]If you're looking to make this baseplate rigid, I'd start with a 5/8" plate min - 9/16" is a bit of an odd ball thickness.[/li]
[li]Your beam above is 8" wide and so is your baseplate. Your tube is 7" wide, and you're calling out 9/16" fillet welds. Total width required is 7" + 2*9/16" = 8 1/8"...not enough room.[/li]
[li]Quick calculation, I estimate you only need about half the strength of the tube - frame sized for deflection, makes sense. That means your 9/16" fillet is way overkill. You can probably get away with a 5/16", and then your weld fits nicely on the beam and baseplate[/li]
[li]My preference for the stiffeners in the beam would be to split an HSS in half and put each half on either side of the beam...basically just continue the column section up into the beam. I don't think there is anything wrong with your stiffeners, this one is just more personal preference - I think my way gives you a slightly stiffer connection.[/li]
[/ul]

 

[slickdeals]

Yes, it is a moment connection.
Refer to AISC Design Guide 24, Example 4.5 for a similar condition.
They have some description in Section 4.2 of the same document.

 

[rb1957]

the only moment connection is that 9/16" weld all round … welds carrying tension loads … sure, it'll take some, but not much.

another day in paradise, or is paradise one day closer ?