Light gauge straps with wood framing
Light gauge straps with wood framing
(OP)
I am working on a 4 story wood building where the owner has requested the wood shear walls be designed without OSB sheathing using light gauge x straps. This seems like feasible option but I have a few concerns.
1. The connection of the strap to the wood wall would be the hardest thing to work out. I can only get about 150 lbs in a nail and I need to develop 2.5 kips. Not to mention how do I transfer the lateral force back into the bottom plate of the wall.
2. I am in seismic design category C. What R value do I use?
If anyone has any experience using this type of system I would like to hear from you about your design approach and any field issues you encountered during construction.
Thanks
1. The connection of the strap to the wood wall would be the hardest thing to work out. I can only get about 150 lbs in a nail and I need to develop 2.5 kips. Not to mention how do I transfer the lateral force back into the bottom plate of the wall.
2. I am in seismic design category C. What R value do I use?
If anyone has any experience using this type of system I would like to hear from you about your design approach and any field issues you encountered during construction.
Thanks






RE: Light gauge straps with wood framing
I think if you use thick enough steel you can make the connections. The problem then becomes applying the finish material over the straps.
If he wants to use the straps, you might suggest using steel studs at the shear wall. Another option might be to use 4x4 posts at your shear wall boundaries, then x-brace the walls with steel rod centered on the wall.
All in all I think experience has shown that the most cost effective system is to use wood sheathing.
RE: Light gauge straps with wood framing
RE: Light gauge straps with wood framing
RE: Light gauge straps with wood framing
They make a number of hold downs that can carry that load - might need to be three inches wide with double studs and a lot of nails - but doable.
There are also threaded connectors that can work
www.strongtie.com
www.uspconnectors.com
RE: Light gauge straps with wood framing
I still am confused as to what R value I should be using for seismic.
RE: Light gauge straps with wood framing
To make this work, a special holddown using end bearing on the shearwall end columns would have to be developed, with special side tabs to install the metal straps. Maybe Simpson will read this post and develop it. Maybe I should have developed it myself and made some money.
Maybe...maybe...maybe never comes.
Mike McCann
MMC Engineering
RE: Light gauge straps with wood framing
This connection has been developed by The Steel Network.
RE: Light gauge straps with wood framing
RE: Light gauge straps with wood framing
RE: Light gauge straps with wood framing
There's also a lot of lateral movement with the nailed connections, and a double thickness of 18 gage plates that the sheetrockers will have to contend with. If this a "X" pattern strapping connection, the straps will tend to pop out the sheetrock when the straps see compression as they will bend out and in normal to the plane of the wall.
Mike McCann
MMC Engineering
RE: Light gauge straps with wood framing
You said the end stud and sill plate will see weak axis bending. It will be minimal won't it??....The vertical component of the brace force will induce shear on the vertical screws and the horizontal component of the brace force will induce shear in the (horizontal) screws in the sill plate. Correct me if I'm wrong but wouldn't the only weak axis bending be induced by the eccentricity of the vertical and horizontal components with respect to the working point?
RE: Light gauge straps with wood framing
Mike McCann
MMC Engineering
RE: Light gauge straps with wood framing
So as the load is applied, force will follow stiffness and the as the weaker stud flexes to avoid the load, the stronger stud (loaded in shear) would take more load, resulting in a non-concentric resisting force, causing bending/eccentricity in the gusset.
The attached sketch shows what I'm talking about.
RE: Light gauge straps with wood framing
DaveAtkins
RE: Light gauge straps with wood framing
Of course there is bending in the gusset plate - adding the gusset strengthens the connection by inducing a moment resisting capability into the connection, and the gusset. As I suggested in my previous post, the gusset's moment resisting capacity would be weakened by cutting out the gusset to either side of the diagonal, clear to the other studs and sill plate, but it would still resist some moment, just a lot less.
Mike McCann
MMC Engineering
RE: Light gauge straps with wood framing
DaveAtkins
RE: Light gauge straps with wood framing
Like I and others have said - hold downs are cheap and easy to install.
Good Luck
RE: Light gauge straps with wood framing
This means that the brace loading is not concentric with the studs themselves and will produce some amount of twist in the wall - or a resultant out-of-plane force.