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Perforated Shear Wall Analysis - Rational Anlaysis vs. ?

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Re:  Timber Design.

 

I’m flustered.  I’ve been working for over two years and have yet to come up with a definitive method for designing shear walls with openings.  I’ve come to find there isn’t one.  I was attempting to use a method that is included in the 2000 IBC ( we call it the “AFPA” method, based on an article I’ve read by Philip Line ) where the ratios of the opening height to wall height and opening width to wall width are used to calculate a reduction factor and require the designer (myself) to increase the nailing in a shear wall.  Over the past year, I’ve read about four or five different versions of that article and now have come to the conclusion that the detailing requirements make it “near-impossible” to make the method work in areas where the walls are SEVERELY impacted.  It makes some sense that any method would have problems when you’re trying to force a wall that’s 18” wide to handle 8000# of shear.  We work primarily with Excel spreadsheets for this sort of analysis, and if there’s a method that doesn’t fit into a spread sheet well I probably haven’t seen it yet.  I also found an “old” spreadsheet in the office archives detailing out how to determine the strap force (and of course the strap callout) above and below window openings, but when trying to follow the equations (going cell to cell) I start to get lost and in the end it’s just a bunch of numbers crunching, and I’m not buying it enough to explain to any plan checker such that they’ll buy it either.  I was hoping that someone reading this list would either be willing to fax a method they’ve used (no numbers – just the method please) or know of a publication or something to help reference a “rational method”.  Every time I ask about this problem I always hear just use a “rational method”. 

 

In case you’re still reading and curious, I have a wall that’s 19’-7” in height and collects and drags load from both the roof (at 19’-7”) and the second floor (at 10’-6”), and otherwise requires 2x6 DF#2 @ 8” O.C. to resist out of plane wind loads.  In fact, wind controls the in-plane design loads.  The total wall length is 21’-6” with a 120-50 window at a header height of 8’-0” and another 120-50 window at a header height of 18’-0”.  The section of wall on the left side is 6’-3” in dimension and section of wall on the right is 2’-9”.  To be honest, I’m fudging the numbers on the dimensions slightly, reducing the length of wall several inches on each.  Using these wall dimensions and the “AFPA” method, I get a 2-sided ½” plywood 10d 2:12 wall.  Ouch. 

 

Oh – and using that old spreadsheet with no real knowledge of how it works or where it’s based isn’t in my interests. 

 

 

Thanks.

 

 

Chris

 

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Christopher S. Campbell
O'Connor Freeman & Assoc., Inc.
225 30th Street, Suite 201
Sacramento, CA  95816
916.441.5721     fax 916.441.5697
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