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Re: SEAOC Seismic Design Manual Seminar - Vol. 1

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In a message dated 8/9/99 11:33:05 AM Pacific Daylight Time, 
Bill(--nospam--at) writes:

<< 3. R penalty on the whole structure
 In the classic case of having a pair of cantilevered steel columns at a
 garage opening (or elsewhere in a wood structure otherwise laterally
 supported by wood shear walls), currently the code reads that the R value of
 2.2 be used for the design of ALL elements at that level in that direction
 including diaphragms, shear walls, etc. Of course, the consensus of the
 engineers I have heard believe this is an unrealistic provision and that
 this issue should be addressed.

Some issues, such as this, have been revised and are expected to be published 
in the upcomming Blue Book. I posted last night the proposed revisions which 
are expected to be adopted at the Seismology meeting. Most crucal was the 
embedded column issues in which they state:
"The introduction of a reduced R factor for cantilevered columns in the 1997 
UBC is partly in response to the damage to tuck-under parking buildings 
observed in the Northridge Earthquake. 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."

I interpret this to mean that it will be acceptable to limit the R factor to 
only the line of shear the columns are applied to but that the engineer 
should be cognizant any effects resulting in torsion to other resisting walls 
tied to the same diaphragm.

My interpretation of the Blue Book comprimise has been that the Seismology 
committee is recommending more allowance for engineering judgment to be used 
on a project and is much less restrictive than the original commentary which 
enforced the provisions of the letter of the code. 

If any interprets it otherwise, please let me know.