huangyhg

light gauge straps with wood framing
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

usually the problem with using steel straps with wood walls is the connections, as you have already found out. unless simpson has come up with a new product, i don't think any of the steel hanger people sell a product intended for this use. if there was an easy way to use the straps with wood walls people, like simpson would be selling it.
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.
it is difficult enough to make light steel strapping work for a single storey building, so a four storey building using this type bracing is ridiculous. sometimes you just have to educate owners that their ideas don't have a basis in reality.
i think you'd have problems getting a strap system to work - i'd agree with hokie66 here. very difficult to connect the ends of the x-straps to the wood and still ensure an adequate load path.

go to simpson or usp.
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
thanks to all for your comments, and i do agree with hokie66. my problem is this owner has already built a building like this with another engineer and now this is the system he prefers. cost is not the deciding factor here as removal of the osb sheathing eases the construction process for the mep trades, and can shorten the shear walls.
i still am confused as to what r value i should be using for seismic.

i hjave seen "ewngineered" solutions that i did not agree with - abortions of the code too. contrary to the owner's comments, just because it was approved and done in the past dopes not mean that it should have been. moreover, codes change.
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
mike,
this connection has been developed by the steel network.
i am feeling some resistance here, and i value you options. take a look at this sketch. i have not addressed the floor to floor hold down but that should be easy say a simpson hd hold-down between floors. how do you feel about load paths? would this comply with all the applicable standards referenced from the ibc?
there's no stiffness in the vertical stud that you are connecting to (in-plane) so you'd bend and break the stud that the gusset connects to. same thing for the top 2x of the bottom double plate.
i agree with jae... to make this work though, you might want to consider the use of a solid wood infill piece at the corner of the wall, thru-bolted between the gusset plates. this should help reinforce the sill plate and endwall studs against weak-axis bending.
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

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