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Re: SEAOC Blue Book C805.3 Lateral Force Distribution

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In a message dated 8/17/99 6:22:52 PM Pacific Daylight Time, 
lhoward(--nospam--at)silcom.com writes:

<< It is clear from this document, that the authors understand the issues
 involved.  At this point the document does not really offer any clear
 cut guidelines on "what to do".  But it does clearly state the problems
 and suggest some ways that engineers may want to approach various design
 problems.
  >>

I just finished reading the document, thanks to Bill Allen's web page, and am 
surprised. It clearly shows how immature this rigidity analysis requirement 
is given the numerous uncertainties in applying it in real life. To 
circumvent the unknowns, it suggests enveloping the design between a rigid 
and flexible diaphragm, as some list members have suggested before on this 
list. This is totally
irrational. Since we are at it, let's envelope our steel beam designs for 
fixed and simple span conditions regardless, so we cover any possibility, and 
forget the economics. Then, why engineer any structure? Let the code dictate 
how every structure should be built and we are through. It's bad enough to be 
an engineer.

Folks, a diaphragm is either flexible or not. It cannot be both. If code 
writers want
a rigidity analysis, they should at least have the tools for us. Otherwise, a 
reduced shearwall aspect ratio, reduced allowable shear values, 3x edge 
members, structural observation, enforcing construction quality control, 
etc., are, IMHO, pretty good containment of any possible performance problem, 
until such time that adequate research and data are available to require us 
do it differently.

I'm sure Charles Greenlaw have something to say here.

Regards,

Oshin Tosounian, S.E.