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RE: Shear Wall Strength Reduction

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All shear and hold down values were devalued by emergency ordinance after the Northridge quake from the old ’91 UBC table 25 K-1.  If you look at COLA Table 2306.4.1 you will see remnants of that ordinance.


I just spent the better part of last weekend beginning the process of updating all my excel spreadsheet stuff to the new IBC, and I couldn’t find that 75% provision in the amendment updates from COLA.  Is it still in there?


I see the 75% for “non-cyclic tested” hold-downs only. 

Am I missing something?.


I think I will probably still use it regardless.  I’ve built enough stuff and seen enough horror in the field to get all warm and fuzzy over a nice fat safety factor that really nearly doesn’t cost the construction anything.




PS:   Got my first taste of ASCE Wind about last Saturday Noon…By Sunday about 11A, I began to get a lot happier about being an Architect and not an SE and began to see a big pressing desire to find a seminar to attend somewhere.   No offense ASCE, but what a pile of it.     FTR, can someone explain how I prove to a plan checker that my house design doesn’t, “…have response characteristics making it subject to across wind loading, vortex shedding, instability due to galloping flutter; and does not have a site location for which channeling effects or buffeting in the wake of upwind obstructions warrant special consideration.”  ???    I hope I’d just have to write above the Method 1 calc,  “This ain’t Florida.” and leave it at that, but I guess somewhere there’s an equation to calculate “galloping flutter” that I don’t know about.


From: bart(--nospam--at) [mailto:bart(--nospam--at)]
Sent: Tuesday, May 06, 2008 6:14 AM
To: seaint(--nospam--at)
Subject: Re: Shear Wall Strength Reduction


you need to get a copy of the LA City building should find it in there....

----- Original Message -----
From: ENGRLAINES(--nospam--at)
To: seaint(--nospam--at)
Subject: Shear Wall Strength Reduction
Date: Mon, 5 May 2008 17:14:40 EDT

My client would like to add a heavier tile roof to his 2-story, wood frame, type V house in the hills of Los Angeles. The second story addition 4-years ago included new plywood shear walls per the 1997 UBC and all evidently permitted. In reviewing the calcs of this addition, I note that the engineer took the Code shear wall values and multiplied them by .75. I cannot find the responsible engineer to query, and I cannot find a Code reference as to why the 25% reduction. These are seismic loads not permanent loads, and the Struc I panels are spec’d with common nails (15/32 Struc I w/ 8d Common @ 3” and 4”). What am I missing?

Charles Laines, S.E.

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