Metal Stud Shear wall

[faromic]

I'm designing a metal stud shear wall the lateral shear at the top of the wall is about 10 kips. The tension compression couple at the end studs is also about 10 kips. I want to use a gusset plate at the corner (screwed to the sill plate (track stud)) and to the vertical studs. The strap will resist the overturning load. The strap will be screwed to the gusset plate, which in turn will be to studs as mentioned above. assuming the angle of the strap is 45 degrees, how do I design the gusset plate? Do I basically design it for the tension over the projected area normal to the strap? The screws connecting the gusset to the studs are then designed for the lateral shear in the horizontal and tension force in the vertical, correct? Does anyone know where to get shear capacities for #10 screws? I didn't look in my Dietrch metal framing catalog yet, but if there is somewhere someone knows of for sure, let me know.
Thanks,

 

[Lion06]

there are values for No. 10 screws, but you will need a lot to get 10 kips. How are you going to anchor the chord to the foundation/wall? I don't know if taking the load into the track is the way to go. Why not just use a simpson Hold Down? I think 10 kips warrants it.

 

[UcfSE]

Use the NAPSEC for cold-formed framing and connections, just like you would the AISC for red iron. It has what you need to calculate your capacities.

What's the force in the strap, and the shear force in the wall? 10 kips isn't too bad for a chord member itself but it could prove annoying in your strap.

 

[faromic]

Yes, for sure. I'm using an HD10 hold down. The strap force is cos(45)*10 kips = ~7 kips. The screws to the track and vertical studs are to secure the gusset, but I don't know the shear capacity of screws and the capacity of the gusset.

 

[hokie66]

Don't know about the screws, but wouldn't the diagonal force be 10/cos 45, about 14 kips?

 

[DaveAtkins]

I am not at work right now, but I know the capacity of a #12 screw in 16 GA steel is 500#. #12 screws are very common.

I am not sure you are following the load path correctly. The 10 kip horizontal force along the top of the wall is resisted by the two diagonal straps (one each side of the wall). The force in the two straps will be about 14 kips, or 7 kips in each strap. The strap should be connected at each end to the track and the doubled up end stud (you could use a gusset plate). The gusset plate should be connected to the sill track (or top track) for the horizontal component of the 7 kip force (5 kips), and to the doubled stud for the vertical component of the 7 kip force (5 kips).

With these large forces, I would use welding, not screws. And keep your gusset plate and strap thickness as thin as possible--it is hard to put drywall over thick gusset plates and straps.

DaveAtkins

 

[wannabeSE]

SSMA (Steel Stud Manufactures Association) has allowable loads for screw in their Product Technical Reference (pg 48).

http://www.ssma.com/ssmatechcatalog.pdf

 

[msquared48]

What Daveatkins speaks of was the construction norm 30 years ago for steel stud shear walls. Back then, welding was common, and there were special inserts to weld the straps to - the gussets you refer to - to transfer the later load to the structure below. There are more design restrictions now though, especially with the "gussets".

Mike McCann
McCann Engineering

 

[shepherd]

If you have the option, there are also proprietary brace connection assemblies. The steel network has some that will give you that capacity.

 

[UcfSE]

You have to pick and choose what you use out of the SSMA guide. It was done using the 1996 CFS code, not the 2001 NASPEC. Some of it can still work if what you're looking at didn't change between codes or the older was more conservative, but you won't know if you don't check.

 

[faromic]

When you are designing the foundations at the reaction points (chords) of the shearwall, how do you distribute the load into the foundation. I have the case where the continuous ftg. along the exterior of the building recieves some pretty large compression reactions at the ends of some of the shear walls. I have a bearing capacity of 1.5 ksf and a load of approx. 8 kips with a 2 ft. wide ftg. I'm just curious if you typically widen the footings at these locations or try (assume that) to distribute the load at a 45 degree angle to the soil. Maybe you can even distribute the compressive load more since I have longitudinal bars at top and bottom of cont. footings?

 

[DaveAtkins]

If you have a foundation wall, it will spread the compression force (for example, a 4' high wall will spread the force 8' parallel to the shear wall).

If you don't have a foundation wall, either use a spread footing as you mentioned or use the strip footing to spread the load along the 5' or so required (2'-6" in each direction).

DaveAtkins

 

[tedamiao]

We specify DARTS Brand SD screws for most light gauge projects. You can find screws tension and shear capacity from ICC report ER-5202.

#10 screws shear capacity on 16GA stud will be 629#.

 

[fredPE]

You also have the option of using an actual sheathing material to make a shearwall, as opposed to straps and gusset plates. Sureboard sheathing is one option for non-combustible applications, and would have a higher R value than tension only straps.