Beam Splice?

[ADAMK2310]

How would you design a splice for cold formed/light guage steel c-studs? The studs do not overlap. They want to use stud material on the backside for the splice plate.

Moment=12k-in
Rafter is 8" CSJ.
How many screws? Screw pattern?

 

[Lion06]

I don't like that idea at all, but the only way I would even consider it is to have a 2' (just for talking purposes) piece set inside the two pieces to be spliced and screw them together. That's the most directt load path I can see.

 

[jike]

If these are rafters, you might want to consider something similar to PEMB roof construction where cold rolled C's or Z's are lapped over the supports and extended past the support until the single member can support the moment at that point.

 

[ADAMK2310]

There is no support. The splice location is 4' from a bearing on a 16' span.

 

[jike]

Adam...

I understand that, but what I am suggesting is to lap the rafters from each side over the support, similar to PEMB construction.

There are some other considerations here that you might want to think about:

Are the splices to be done "up in the air" or "on the ground"? I suspect "on the ground" and lifted into place since a worker would need to be on a scaffold if he will make the connection "in the air".

If done "on the ground", then you need to consider stresses in the connection from lifting it into place.

 

[ADAMK2310]

Sorry, I'm not familiar with PENB construction.

 

[jike]

PEMB = Pre-Engineered Metal Building

 

[K2skis]

Are you transfering bending and shear through your splce or just shear forces with the one beam cantilevering out the 4' and supporting the 12' span?

 

[BAretired]

I suggest a bent plate in the shape of a channel applied outside of the rafter. A lap of two feet on each member would seem reasonable. Provide enough screws to easily resist the applied moment. Do not attempt to save pennies on the connection.

BA

 

[csd72]

Buckling could be a big issue for this, make sure that the member is restrained against buckling on each side of the connection.

 

[ADAMK2310]

Addressing the previous post: I am attempting to transfer bending and shear.
One suggestion was to treat it like an eccentric load on a bolt group. (instantaneous center concept). Do you think that is an acceptable theory?
That method would require 10 screws on each side:
2 horizontal rows of 5 screws. Row spaced 6" apart. Screw spacing = 2" Any thoughts?

 

[rb1957]

that looks good to me ... a fastener group reacting shear and moment, remember the vector addition of the two forces on ech fastener.

you also need to check the joint plate itself, between the two fastener groups ... it'll be smaller than the stud section, no?

 

[ADAMK2310]

They want to use a piece of the 8" stud (attached to the backside) for the splice plate.

 

[ron9876]

I don't like the sound of this either. Must be sure the numbers work. If this is one of several rafters may not be so bad but I wouldn't splice several in a row.

You can add a heavier piece of track over the stud. The flanges are screwed for the tension/compression and the shear is transferred by moment on screw groups. The trick is getting the contractor to place the screws where you designed for the moment resistance.

 

[CFSEng]

I'm with ron9876 on this one. If you are trying to splice 2 studs together I would recommend capping the back side with a heavier piece of track and screwing the flanges and webs. Is there a reason they are pushing for using a stud on the back? Normally you would only attempt this if the stud already has sheathing on one side so you cant install the cap track.

 

[ADAMK2310]

I am told that scabbing a stud on the back is a standard repair for this situation. Also, I think there are several rafters in a row.

I like the track idea. You could attache the web for the shear, but how would you figure the # of screws in the flanges?

 

[CFSEng]

As a quick answer you could take the moment divided by the depth of the stud (12/8=1.5) and design the connection at the flanges for 1.5kips. You could also check M/S to get the stress in the flange and go from there. Keep in mind there is more going on than just the screw connections, you must be able to transfer the moment between the two pieces. Make sure your splice track can transfer the moment/shear/web crippling forces needed.

While the scab piece on the back could work (have to make sure the screws are properly installed) the cap track method is a little more simple to use and has more redundancy in my opinion.

 

[ADAMK2310]

I agree with that answer. The stud scabbed to the backside requires a precise screw pattern, thus making the installation critical.
Using track attached to the web and flanges to transfer the forces is a superior design. I just need to make sure the track can transfer all of the applied forces.
Thanks CFSEng!

 

[BAretired]

If necessary, use a heavier gage track section.

BA

 

[hokie66]

Just scabbing a stud to the back does not transfer the bending properly. You need to transfer the flange forces directly, not over and back. Use the top, bottom, and web approach, developing all three.