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Re: Effects of the New Code on Wood structures - good or bad????? -Part 1

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Mark, the answer is very simple - none of these provision were either 
applicable to wood framed construction with wood diaphragms until 1988 and 
none of them were either enforced or consider the "Standard of Practice" for 
wood framing until this code cycle.
The actual reason is not known just why the provisions were not enforced 
prior to 1997 UBC but it is suspected that it was because there was no 
rational means to calculate the deflection of a flexible diaphragms (and 
there is only a multiplier suggested by APA at this time) and the provisions 
in the code could not be satisfied.

Why all the ranting and raving as you put it? The code rationale is very 
straight forward if you are dealing with a simple geometric shaped building 
with a great deal of simplicity in the diaphragms and transfers of shear from 
floor to floor. This is typical of most commercial and industrial projects. 
It may even be somewhat easier considering a simple small residential 
structure that is fairly rectangular with few irregularities.
Once you get into the design of a structure that is neither rectangular, with 
multiple levels offset from one another (such as split levels), roofs that 
frame upon one another or diaprhagms that cantilever and any other creative 
avenue that the architect dreams of, the design difficulties grow 
exponentially. 
Now if you reread all of my posts, you can begin to see the difficulty that 
this creates for almost all of us who specialize in wood. Most of us feel 
that the ends don't justify the means - there is not sufficient evidence to 
justify the change nor is there sufficient damage attributed to justify my 
rants (I don't rave about this code).

I will review part two and respond.

Dennis

In a message dated 7/22/99 12:57:50 PM Pacific Daylight Time, 
Mark.Swingle(--nospam--at)dgs.ca.gov writes:

<< Since at least the 1967 version (that's as far back as I have looked),
 consideration of the following three items has been required for earthquake
 design (and wind design) in the UBC: 1) The relative stiffnesses of the
 various shear walls with respect to one another, 2) The relative stiffness
 of the diaphragm vs the shear walls in each line, and 3) The eccentricity
 between the center of application of the forces and the center of rigidity
 of the resisting elements.  These three items have not changed, and these
 are the main issues that you imply have changed so drastically in the 97
 UBC. >>