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RE: new SEAOC seismology web page

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That is almost right. When SEA first incorporated the NEHRP provisions the changed the R values for working loads by dividing by 1.4 and rounding to achieve the Rw values. When they went back to Ultimate loads they forgot to go back to the NEHRP values and just multiplied by 1.4 yielding slightly different values.

> -----Original Message-----
> From: Bill Allen [mailto:Bill(--nospam--at)AllenDesigns.com]
> Sent: Wednesday, December 22, 1999 4:00 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: new SEAOC seismology web page
> 
> 
> Me first! Me first!
> 
> Ref: 1997 UBC Code, section 1633.2.9.3 (R not exceeding 4).
> 
> In the old code, 1994 UBC, section 1631.2.9.3, the limitation 
> was Rw<=6.
> When designing wood framed structures under the old code 
> using a Rw=6 (Table
> 16-N, item 1.1.b), this requirement was invisible. Now, the 
> designer is
> required to produce MORE (IMO tedious and worthless) 
> structural calculations
> for the same structure since R=4.5 for item 1.1.b in Table 16-N.
> 
> My Question:
> 
> It appears to me that Table 16-N and section 1633.2.9.3 were 
> given to two
> engineers to translate to the 1997 UBC code language (i.e., 
> divide by 1.4)
> with one engineer rounding up to 4.5 in Table 16-N and one 
> engineer rounding
> down to 4 in section 1633.2.9.3 and the seismology committee failed to
> coordinate the two. Is this the case or has the seismology committee
> discovered some scientific data or anecdotal evidence which, 
> in the interest
> of life safety, warrants the additional structural 
> calculations? Or, should
> UBC section 1633.2.9.3 be amended to read "...R not exceeding 4.5."?
> 
> Regards,
> 
> Bill Allen, S.E.
> ALLEN DESIGNS
> Laguna Niguel, CA
>