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Re: LADBS Info Bulletin ST-12

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Basically, you still have to use the reduced allowable loads for shearwalls 
and holdowns, regardless of the analysis method used. If you assume flexible 
diaphragm in your load distribution, and use the static force procedure, then 
you have to increase your loads by 20% for sizing your shearwalls and 
holdowns, which is equivalent to using 60% of allowable shear and holdown 
values, and this is the Alternate Basic Static Procedure.  However, if you 
use the Simplified Static Procedure, your loads are already 20% higher than 
the previous method (3/2.5), and, therefore, you need not increase the loads 
further. Of course, you can divide your loads by 1.4, except for drift 
calculations, which is normally not required unless you have flexible 
elements as stated in one of the conditions for assuming flexible diaphragm. 
And, of course, you multiply the loads by rho, if it exceeds 1.0.

Hope this helps,

Oshin Tosounian, S.E.
Los Angeles

In a message dated 7/27/2000 6:53:56 PM Pacific Daylight Time, 
RLFlower(--nospam--at)worldnet.att.net writes:

<< The City of Los Angeles Department of Building and Safety has published a
 draft of an Information Bulletin, dated January 27, 2000 and revised May 15,
 2000. It is entitled "Interim Alternate Method for Distribution of Lateral
 Forces in Wood Frame Buildings Assuming Flexible Diaphragms." The scope of
 this bulletin is to address the issue of the code requirements for diaphragm
 flexibility and story drift in wood-frame buildings.
 
 This draft bulletin gives the option of using the Basic Static Force
 Procedure, employing shear wall displacement analysis and story drift
 limitation, or using the Simplified or Alternate Basic Static Force
 Procedure, employing "Conditions for Assuming Flexible Horizontal
 Diaphragms."
 
 For anyone who is up on this stuff, my first question is: has this draft
 document since been revised? Secondly, has there been further explanation
 given for the last condition listed: "shear panels and hold-downs provided
 shall be designed to exceed the design load by at least 20%."?
 
 Specifically, I cannot for certain determine just what is the "design load".
 Is this 75% of the values listed for vertical shear panels in the Los
 Angeles Building Code? If this is the case, then are we to take 20% off of
 these reduced values, resulting in 60% of the listed capacity? And, the same
 for the holdown hardware?
 
 Thanks in advance for your informative response.
 
 Richard L. Flower, P. E.
 Los Angeles
  >>


Oshin Tosounian, S.E.
Los Angeles, CA

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