Steel Stud Stub Column 1

[KOTOR1]

I am reviewing some shop drawings where a wide flange beam bears on steel stud columns (3 studs together 8" studs 68 gage). There is a 1/4" thick bearing angle on top of the stud column to which the beam is attached. The studs are welded to this angle. This occurs at the corner of the wall. The load is about 8 kips. Is using steel studs for supporting wide flanges ok?

Secondly, there is no base plate as such, the studs are supported on the bottom track. I am told this is fairly standard by our senior engineer. Is there anything, I need to look at in terms of crushing of the track due the load?

 

[mike20793]

Yes, it is okay to support steel beams on cold formed studs. I would stitch weld the studs together.

 

[XR250]

That is a pretty standard detail and will likely work if the studs are attached together to act compositely.
If I was the EOR, I probably would have shown a red iron column.

 

[KOTOR1]

I looked at the calculations prepared for the project and they are using #10 screws at 12" o.c. to attach the studs together as shown in the shops. Is stitch welding preferred?

Is there anything special that needs to done at the bottom track?

 

[XR250]

How are they stitching the studs together without intermediate tracks? Welding is best as it eliminates the need for intermediate members.
If there is no uplift, usually the studs just bear on the bottom track and are screwed thru the vertical leg.

 

[KootK]

Issues I've encountered.

1) It can sometimes be difficult to obtain convincing lateral torsional buckling restraint for the beam ends at the bearing locations. At first blush, your detail sounds as though it's probably okay.

2) If the load is heavy enough to warrant a wide flange beam, it may also be approaching the point where a steel plate nested in the bottom track might be required to distribute the load to the concrete. Otherwise, the track must do that job.

3) In a built up column of any material, you want the axial load to be shared by all of the plies. And, even with top bearing, that's rarely the case. Ideally, I'd like to see a concentration of ply shear transfer connection at the top and bottom of the built up column to quickly distribute the load. Welds are great for that.



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.

 

[KOTOR1]

The studs are attached back to back with screws along with tracks at the edges per the attached file. The beam attached to studs is designed as completely unbraced. Two 12" studs back to back works as the beam. The wide flange was a client requirement.

 

[XR250]

That looks sufficient

 

[KootK]

The beam attached to studs is designed as completely unbraced.

While I get what you're saying, it's important to recognize that even an "unbraced" beam requires bracing / rotational restraint at tbe supports.

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.

 

[KOTOR1]

KootK,

So it would be much more preferable to use welds than screws then? The wall will be fully sheathed on both sides as well.

 

[KootK]

I like the welds better mechanically but would not object to the use of screws. At the end of the day, the cheapest thing that's good enough is the right answer.

As a hypothetical, consider a case where your beam end rotates and that results in most of the axial load being delivered to the ply of the column nearest the beam span. How many #10 screws at 12" o/c would it take before you could call that load properly distributed to the other side of the built of column? And how far down the height of the column are you at that point?

Sheathing may help some with bracing the wall but it wouldn't do much for load distribution between plies of the built up column.

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.

 

[Teguci]

How many #10 screws at 12" o/c would it take before you could call that load properly distributed to the other side of the built of column?

For 2 member composite element, AISI requires that the ends of the built up members have a weld length = to the max width of the member or connectors at 4 dia spacing for a distance of 1.5 x the max width. Spacing = 3/4" over 12" for the top and bottom zone. - ref AISI S100, D1.2

I think the intention is to design the connectors to transfer the full compression/tension capacity of 1-section to another at the top and bottom zones.

 

[KootK]

Thanks for that Teguci. With those provisions satisfied, I'd have much greater confidence in using screws for lamination.

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.

 

[KOTOR1]

Thanks, I will update the shops with the screw pattern top and bottom.

 

[XR250]

As a hypothetical, consider a case where your beam end rotates and that results in most of the axial load being delivered to the ply of the column nearest the beam span. How many #10 screws at 12" o/c would it take before you could call that load properly distributed to the other side of the built of column? And how far down the height of the column are you at that point?

Just like wood construction, things will crush and deflect as needed to transfer the load where it needs to go.
I would not worry about 8 kips in this case.