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RE: SStud: Need opinions about residential construction and steelstud shearwal

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-----Original Message-----
From:	MGriffi119 [SMTP:MGriffi119(--nospam--at)aol.com]
Sent:	Friday, December 05, 1997 11:55 PM
To:	seaoc(--nospam--at)seaoc.org
Subject:	Re: SStud: Need opinions about residential construction and steelstud shearwal

Not wanting to sound redundant, but if 14 or 12 gauge material is used for the
wall framing, is stud buckling still the failure mode? My understanding was
that for 14 gauge wall studs, combined with double or triple stud, welded
jambs, the plywood and/or the sheet metal screws fail. (for 1/2" plywood). Is
this not correct? If it is correct, just use 14 gauge framing for the
shearwalls and be done with it. Obviously, the contractor's hate 14 gauge
material because they have to predrill the holes, but last time I checked,
contractor's don't make engineering decisions. Right?
                                                     Monte Griffiths, RCE


[Dennis S. Wish]  The mode of failure that we mention, if I understand you correctly, is in the studs of the shearwall subjected to compression by action of the applied lateral load. I'm not sure if the panels are gravity loaded when tested as a shear element. Typically, we use 20 ga studs throughout except were specifically designed as a shearwall - then I personally have followed the values recommended in APA Report 154 and specified the studs in accordance with the resisting values I need for shear.
I have not seem much in the way of welded jambs in small residential construction, but your next comments bring up an interesting question:
One of the problems with steel stud shear walls was the ability to get the plywood (or OSB) tight to the face of stud. Stud pins (0.144" dia x 1-1/4" long pneumatically driven tempered steel) were recommended compared to standard metal screws. However, "winged" ply-metal driller (self-tapping sheet metal screws with wings for widening the hole in plywood) make an excellent alternative that taps the hole in the plywood sheeting a hair larger than the diameter of the screw. The "wings" shear off in the stud and pull the plywood tight to the face of stud.
The problem is that ply-metal drillers are intended for 18 gauge or thicker studs and are not very effective on 20 ga studs. This problem came up in the field and we were able to compensate by reducing the speed of the screw-guns which helped to shear the tabs off in thiner materials.
BTW, ply-metal drillers do not need to be pre-drilled (self-tapping) which should save your contractor a few bucks.
If we move to thiner studs (20 ga) we may be faced with a problem in trying to get a tight connection between the panel and face of stud.
I also agree that contractors hate the thicker gauge studs. In my area, it's not because it is any more difficult to handle. Historically they have used 20 to 24 gauge on all of their projects since they never required engineering in outlying areas and were accepted based upon the advice of the supplier. Then the old engineer got involved and screwed everybody out of profits by increasing the material thickness, creating load path connections, improving performance of shearwalls - all the profit cutters that we are resented for. 
Sorry if I sound bitter, but we get blamed when a failure occurs, blamed when we overdesign and blamed when design by code. Oh yes, we are blamed for the code as well.
The real problem is that few people like to have a professional step in and upset the apple cart - they simply don't believe that it is motivated by public safety or mitigation of potential damage.
Best regards
Dennis Wish PE
 

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