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Re: '97 UBC Lateral Design - Envelope Solutions???? Calmed down reply

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Sorry, I might have lost my temper. I considered this paragraph a personal 
attack. With that said, I don't agree with you. The code only defines one 
extreme or the other since it fails to instruct the designer what to do if a 
condition occurs in between - which can not happen. There is no test in the 
code that defines a point when the calculated plywood diaphragm deflection 
equals 2 times story drift as between rigid and flexible. If it equals 2 
times the story drift it is considered not-flexible - which in my book means 
rigid. If it is EQUAL TO or greater than 2 times the story drift it is 
non-rigid, which again in my book of definitions means flexible. There is no 
in-between unless it is in-between the lines in hidden ink:>)

This ambiguity that you are arguing is an example of the flaw that occurs 
when Seismology trieds to include wood structures with wood diaphragms into a 
"methodology" defined by these sections of code and it does not.

There can be only one answer.
1. If the diaprhagm deflection is less than 2 times the story drift the 
analyisis distribution of shear through the diaprhagm is calculated 
considering the contribution of shear from torsion in the diaprhagm.

2. If the diaprhagm deflection is equal to or greater than 2 time story 
drift, the shear may be distributed through the diaphragm by tributary area.

3. A combination (envelope) of the above.

Distribution of shear in each line of resistance to walls within that line 
are designed by relative stiffness. This is a separate issue - however, the 
force distributed to these walls is either greater or less than that 
calculated by either method one or two above. 

Which of the three choices do you think will be justified in a court of law 
if damage is incurred on the struture and the EOR designed by either method 1 
or 2 only? Do you think that the opposition will not have an expert to debate 
the possiblity of Option 3 because of the ambiguity in the code? 


In a message dated 9/23/1999 5:26:45 PM Pacific Daylight Time, 
Mark.Swingle(--nospam--at) writes:

<< (MS) Sorry, Dennis, but if you are going to rant like this, READ THE CODE.
 The code does not use the phrase "rigid diaphragm".  It is not an either/or
 situation, it is a continuum, with the only exception being that all
 diaphragms that meet the test are deemed to be 100% flexible.  However, most
 diaphragms in residential construction are neither 100% rigid nor 100%
 flexible, they fall somewhere between.  We have been through this before
 several times, Dennis. >>