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RE: Rigid Diaphragm Analysis

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|I believe wood frame buildings (wood shear walls and diaphragms)
|should always
|qualify as "flexible"
|When we consider wood diaphragms combined with non wood elements (frames or
|concrete walls) then I think we need to be more careful.
|
Bob:

If this is the case, wouldn't a concrete shearwall or braced frame be even
stiffer relative to the diaphragm compared to a plywood shearwall and
therefore justify a flexible diaphragm?

I am amazed that the "rigid or flexible" controversy can have any merit at
all when the basis for plywood deflections are inaccurate. Wouldn't this in
itself render the code language inappropriate? The notion of determining
stiffness relationships between plywood diaphragm and shearwalls for wood
framed residential homes is flawed since the empirical formulas for
calculating deflections does not take into account the potential
*significant* effects that the complete building materials can have on the
overall building behavior due to lateral loads. For example, how do you
determine the effects of hardwood floors, hardi-board, siding, mortar and
tile or gypcrete? Have glue nailed floor diaphragms ever been  tested or
screw shank nails? Isn't it equally cavalier to assume that they have no
effect? Furthermore the empirical formula for plywood shearwall deflection
was based on tests for 1:1, 8 foot tall shearwalls only, right? My
conclusion is that the relevant sections of the code are inherently flawed.
Until we have full scale tests of real assemblies, I agree with Bob, that
wood framed residential buildings should always qualify as "flexible".

Regards,

Jeff Smith


|Dennis:
|
|What about getting ICBO staff to publish an interpretation in
|Building Standards
|Magazine on the issue?
|Most building officials will accept such a statement.  The
|question might simply
|be:  Does Section 1630.10 apply to buildings having a lateral
|system consisting
|of wood diaphragms and shear walls that comply with Section 2315?
|
|I believe wood frame buildings (wood shear walls and diaphragms)
|should always
|qualify as "flexible"
|When we consider wood diaphragms combined with non wood elements (frames or
|concrete walls) then I think we need to be more careful.
|
|Bob Bossi
|