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Blue Book Revisions for Wood Framing

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I sent this last night and wondered why there was no response. I looked at 
the post that I received and it stated that the email was too large for 
posting on the list. Therefore, I will summarize the revised 2000 Blue Book 
Wood section that I received yesterday from Saif Hussein, SE who is the 
current Chair of the Seismology Committee:
Please don't write me for a copy of the draft. I sent it to Shafat and asked 
him to post it on the Website for those who are interested.
This is a summary and it is not my intent to misrepresent the text by taking 
sections out of context. It seem approriate to summarize the highlights of 
the document. 

Embedded Columns R values - this was the most heated of the controversy's:

"The relative flexibility of cantilevered columns compared to parallel shear 
walls is thought to have been one factor contributing to the poor performance 
of buildings with tuck-under parking in the Northridge 
Earthquake..........Although damage resulting from the of relative 
flexibility of vertical elements should theoretically occur to varying 
extents in many other types of wood buildings, it has  not yet been reported 
as a major cause of damage."
"Modification of Section 105.4.4 in this edition of the Blue Book now 
recommends the application of the lower R factor just to those elements that 
are along the same line of resistance as the cantilevered columns."

Rigid Diaphragm Analysis (Torsion):

"Earthquake damage observed to date suggests that the Life-Safe Performance 
Level, as defined in Vision 2000 Part 1, has generally been achieved where 
structures with wood structural panel diaphragms designed using flexible 
diaphragm assumptions have a fairly regular configuration and redundancy."
"Consideration of rigid diaphragm behavior is recommended where the 
diaphragms can be judged by observation to be stiff compared to the vertical 
lateral-force-resisting elements, and particularly where one or more lines of 
resistance are substantially less stiff than the rest."
"For small, substantially regular buildings that have a good distribution of 
lateral resistance and are well tied together, earthquake performance to date 
suggests that design using flexible diaphragm assumptions is adequate for 
Life-Safe Performance. It has been suggested that one and two-family 
residences be given blanket exemption from consideration of the applicability 
of rigid diaphragm analysis.  Such a blanket exemption does not, however, 
make sense from an engineering standpoint because many one and two-family 
residences now being designed have highly irregular configurations with low 
redundancy and significant discontinuities in the structural system."

Shearwall distribution by rigidity:

""As a result of aspects like these, the creation of fine-tuned calculations 
of shear wall relative stiffness for purposes of lateral force distribution 
does not make a lot of sense.  It is necessary to apply engineering judgment 
to the information available.  Approximate methods of evaluating relative 
stiffness may be appropriate, and a simplified evaluation of stiffness used 
with engineering judgment may well lead to more realistic results than a 
numerically rigorous method. "

Legal Liability for non-code compliance in past:

"Past and present design practice in California and other areas has almost 
exclusively used flexible diaphragm assumptions for distribution of seismic 
forces in structures with wood diaphragms.  While design using structural 
materials other than wood had considered rigid and occasionally semi-rigid 
diaphragm behavior prior to the 1988 UBC, design of wood structures had been 
based on the assumption that all wood diaphragms behave in a flexible manner."

"Although damage resulting from the of relative flexibility of vertical 
elements should theoretically occur to varying extents in many other types of 
wood buildings, it has  not yet been reported as a major cause of damage.  
Earthquake damage observed to date suggests that the Life-Safe Performance 
Level, as defined in Vision 2000 Part 1, has generally been achieved where 
structures with wood structural panel diaphragms designed using flexible 
diaphragm assumptions have a fairly regular configuration and redundancy.  "