Moment Resisting Bracket

[Trainee339]

Hi All,

I am designing the moment resisting bracket for cold formed steel stud wall. I calculate the base moment and reaction and calculate the shear forces in the bolts connected to the stud (Bolt Pattern Force Distribution). and similarly used hilti profis to check the bolt capacity. My question is if I use the two bracket (as shown in the attached sketch would it be same? any cons of using 2 brackets instead of 1?
Need your thoughts.

 

[Tomfh]

The first one is stiffer but I’d consider both of them pinned connections.

 

[Trainee339]

Hi value of moment = 0.117 KN-m. It is a short wall of 700mm high (inside the enclosed building).
any other thoughts?

 

[XR250]

No need to re-invent the wheel...

https://steelnetwork.com/Product/StiffClipCL

 

[phamENG]

XR250 is right - there are several manufacturers who make these. But on the off chance you find yourself on a remote island with no access to global construction markets but somehow have an abundance of steel to fabricate these....

Number 1 is preferable. Number two won't be as stiff, and the spacing between anchors will vary - there's no fixed distance. You may tell them to put them in at 4" o/c, but it may end up being 3.25". That's a huge difference when dealing with large-ish moments and a small e distance for your force couple.

A note on increasing stiffness - whatever you think the thickness of of your bracket should be, add a plate at least 4x that thickness to the bottom.

 

[Trainee339]

Thanks XR250! But I am based in Australia and client won’t order from the USA.i already suggested them.
PhamEng. Thanks for your detailed response.

 

[Tomfh]

Trainee, your first bracket is better. The main issue is your bolt connection to the stud allows too much slip. You are better off with multiple small fixings as per the other bracket listed above. You can achieve this with multiple widely spaced tek screws between the bracket and stud.

 

[Trainee339]

Hi Tom,
My original design is the bracket with 4#14g screws with the stud. But client engineer is trying to convince me to the put this as a option in my design specifications (as these brackets with bolts holes are readily available in Australian market).that is why i am looking for all the valid reasons to say no or yes.
I agree with PhamEng as well that on site they wont be able to maintain the distance between the brackets which is critical.

 

[rb1957]

ah, but isn't that part of the equation. the two design options are almost equivalent, sure I think we'd opt for design 1 given our choice to choose.

but the double brkt pieces are more readily available, shifting the design choice that way ?.

Would it be unacceptable to buy a long blank angle piece and cut and drill to suit ? I imagine there are 100s (1,000s?) of this detail so a small cost difference in the designs can become significant.

How much moment comes out to a wall stud anyways ? Surely these are usually installed with just a couple toe nails ?

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

 

[KootK]

that is why i am looking for all the valid reasons to say no.

It's not that the two bracket thing can't be done. It just changes the stiffness and mechanism of resistance in ways that will be inefficient in the material sense. Your bolt tensions and embedments will rise, your plate thickness will increase, and you'll introduce what I'd call a soft shear deformation mechanism at the bottom. And you'll invite all of the difficult to evaluate flexibilities that will accompany these things.

For me, this would be one of those situations where I'd tell the client this story: Yeah, I can design most anything. You just may not like what that winds up costing when all is said and done. Unless these souble clips are coming at a very serious discount, I'd have to think that the single clip will be the most economical solution.

 

[Tomfh]

Trainee, you can use the same brackets and screw the stud to the metal.

For such low moment you can probably just crank the bolts up tight and rely on friction. If you get to the point you’re relying on bolt bearing the wall will have rotated a fair amount.

 

[r13]

KootK's sketch is quite impressive. The pin/bolt connection makes me reluctant to call this is a "moment connection", partial maybe. Also, it depends on the flexibility of the connected part.

 

[Trainee339]

I am very thankful to everyone. Especially Kootk for his well explaining sketch.I have few other points to not recommend to use it as these angles are not galvanized, so galvanizing them will increase it's cost. And it will hard for them to cut the exact holes at the exact location in the stud ( it will also result in lose connection).
Thanks

 

[XR250]

The shear loads on these systems are usually quite low as the anchor pull-out and clip deformation usually are the limiting factor due to the long lever arm.
I imagine if the bolts are sufficiently tight, KootK's "soft story" issue would not be an issue. Assuming this is the case, option 2 seems easier to analyze.

 

[rb1957]

"it will hard for them to cut the exact holes at the exact location in the stud" … ? the studs are pre-drilled ?

if hard to align the single fastener small clips, then it'll be harder yet to align the clips with two holes. Clip holes should be slightly oversized to allow for position tolerance. Drilling holes in both parts (for ease of assembly) requires careful consideration of the tolerancing.

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

 

[phamENG]

rb1957- you're spot on. That's why most of the mass produced clips for this application are fastened using self drilling screws to take the alignment tolerances out and tighten up the connection.

 

[KootK]

I imagine if the bolts are sufficiently tight, KootK's "soft story" issue would not be an issue.

Yes, if one is willing to call a single bolt with next to no stretch length a reliable, slip critical, single bolt moment connection. Obviously, it would be nuts to do that for anything of any importance.

 

[rb1957]

@Trainee339, are you using self tapping screws (see phamENG's post above) ?

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

 

[Trainee339]

thanks again to everyone. Let me share bracket client sent me to have a look.


It is 40x40x5mm thick. with M10 bolt/anchor. He want to use two of the bracket to the web of the 92mm stud, with 10mm gap between with them (0.75BMT stud). As I checked on hilti Profis and it requires 50mm gap between M10 anchors. The holes will not be pre-punched they will use hole saw on the site to cut.
My custom bracket design comes with 4#14 screws but he is asking me to included this angle detail as an option (this will be one bolt connection with stud in the middle ( as i showed in t the sketch).

thanks

 

[Tomfh]

That bracket is no good.

There are plenty of more suitable brackets available from Bunnings if that’s where they want to buy form. They have brackets ranging from 0.6mm to to 6mm thick, including those that look like your bracket.

Search angle bracket on their website