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Re: shear wall programs

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In a message dated 4/14/99 8:19:38 PM EST, NDZ28(--nospam--at)aol.com writes:

<< Does anyone know of any programs that would facilitate  the design of 
plywood 
 shear walls and analyze plywood rigid/flexible diaphragms. Even a good 
spread 
 sheet would help, but I  wouldn't even know how to start one i.e.; Excel. 
 Thanks
 Andy >>

When looking at some of the available commercial programs, take a look at how 
they address holdown assembly deflection (stretching, oversized holes, wood 
shrinkage, crushing, etc.) since these greatly influence the shear wall 
deflection.   How they evaluate the allowable holdown size based upon drift 
load forces vs. working stress design forces.  Also how do they address 
overturning forces from walls above, and do the upper floor walls which stack 
include the holdown deflection from the floor directly below.  The typical 
detail of a holdown above and below the floor line at the upper floors 
increases the amount of shear wall deflection (two holdowns should be 
considered for deflection).

If you write your own program, I suggest that you include flexibility for 
setting nail size and spacing for individual walls, holdown sizes and 
corresponding deflection characteristics, amount of wood shrinkage to 
include.  The more flexibility the better for adjusting variables, especially 
if you have to evaluate an existing wood buildings.  

Be aware that certain codes being developed want you to increase the 
calculated shear wall deflection by 1.25 due to dynamic effects.  The best 
program will be one which iterates on its own so all walls that you enter 
into the program (2,3,4,5,6 walls etc.) will have the same deflection.  You 
may find it very time consuming, if you have to keep changing a variable such 
as holdown size for individual walls till you get all walls to converge to 
the same deflection (say +/- .01" difference between the maximum and minimum 
wall deflection for all walls analyzed, remember that you are likely looking 
at a maximum allowable drift of around 0.5" for an 8'-0" wall).

The deflection of these individual walls can then be used to determine wall 
stiffness to do the rigid diaphragm analysis.  Based upon the rigid diaphragm 
analysis, you may have to increase the wall strength (holdown sizes) to meet 
the increased forces due to torsion.  Hopefully in the near future, the 
commercial computer programs will be able to handle this.

Michael Cochran