Light Framed Walls w/ Flat Strap Bracing

[theonlynamenottaken]

I am designing some three-story, light framed (wood) apartment buildings. The contractor wants to use flat strap bracing as opposed to sheathing on "shear walls".

I was provided an old set of drawings indicating Kant Sag flat strap "wrapped around" the bottom and top plates. I contacted USP (who bought Kant Sag), and they informed me that the flat strap bracing system is really only for erection stability and that there are no systems out there for shear walls. Furthermore, there are no strap systems that include bending or wrapping strap around the plates.

My quick hand calcs show needing ~3500# strap force - but terminating the strap w/ ~50 nails on ~10 studs at each end of each shear wall is not practical. Anybody have any knowledge of this system or any manufacturers providing these products?

 

[DaveAtkins]

I agree with USP. You need to use sheathing. If you can't have OSB on the exterior, can you make the interior GWB work?

DaveAtkins

 

[msquared48]

This strap bracing was more in use with metal stud walls 20 years ago. Kinda outa date. Plus the end connection of the strap and plates to the studs ARE a bear to justify for the loads seen. Welding made it simpler with the metal stud walls. So...is the solution weldwood?

I agree with Dave.

Mike McCann
McCann Engineering

 

[MiketheEngineer]

You might check IBC2003/6 or whatever code you are following for a list of available methods..

 

[lsmfse]

Simpson Strong-Tie has several models of similar tpyes of straps. However, the Code(2001 CBC) limits when and where you can use these straps. Personally, I wouldn't use these straps to resist lateral loads due to wind or seismic. Educate the contractor and use plywood or OSB shearwalls.

 

[theonlynamenottaken]

I initially told the contractor that I wasn't comfortable with strap bracing unless a precedent could be shown. You guys don't seem to know of a known and tested system (for wood walls). The contractor couldn't produce a precendent - so I've already gotten him to surrender to sheathing.

I just wanted to see if this was a common, known and tested system that I had just not yet encountered. You can never stop learning...

 

[csd72]

Metal strap bracing stud walls are very common in Australia, where walls are very rarely clad in plywood.

Wind there can get just as strong, but seismic is not really an issue there.

 

[theonlynamenottaken]

csd72

Like I said, I already got the contractor to surrender to sheathing. However, I would like to know more about those systems if you have any info. Do you know the manufacturer's name for any of those systems? Or do they use common flat strap and have some "trick" for the end connections?

Thanks

 

[JKW05]

I can't find any restrictions to their use with light-gauge, and there seems to be some steel stud manufacturers that are still listing shear wall capacities with straps. I do agree trying to get the load from the strap into wood framing would be nasty, and it certainly isn't permitted for "Conventional Wood Framing" per the IBC.

msquared...

It's been a while since I did light-gage framing, but I often used straps with steel studs. Are you suggesting it is "out of date" for light-gauge or wood (or both)? Just curious about your experience(s).

Thanks

 

[msquared48]

JKW05:

The light gage systems I have seen recently do not use straps, but an ICBO rated system of either plywood or gypsum wallboard screwed to the metal studs. I guess I should say that as far as I have recently seen professionally, the practice is obsolete.

Mike McCann
McCann Engineering

 

[dik]

About 25 years ago, the steel contractor forgot to install the x-bracing and the steel stud wall had been constructed (about 16' tall) and the clay brick, insulation and sheathing had been constructed.

The contractor 'fished' metal strap (16 or 18 ga, I don't recall) and it was pop rivetted for splices and final attachment at the columns... First time I used straps and pop rivets and the building is still standing. If straps work for serious commercial stuff, they should be able to be used for houses. I had a difficult time getting load capacities for the pop rivets.

Dik

 

[JKW05]

Thanks Mike. If I recall correctly, you are on the west coast(?). Do you think the use of straps may be less preferable in the higher seismic regions? (I'm in PA).

 

[AmandaM]

See the following website for one of Australia's manufacturers of flat strap bracing:

http://www.pryda.com.au

I worked in the west for many years and have never used or heard of the straps for conventional wood framing, in the midwest they are used often in residential construction, but only as bracing and the walls are sheathed with either OSB or R-Board.

 

[msquared48]

JKW05:

Yes, I'm on the west coast, and regarding your statement on the high seismic regions, that could be the reason why I have not seen any in quite a while. Unless it is IRC or IBC prescriptive, any shear wall system has to be a tested, rated system, ICBO or otherwise.

By the way, when the big one hits here, I expect my property value to go up. I'll have waterfront property!

Mike McCann
McCann Engineering