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Re: Wood: Stronger lateral design measures vs. improved construction

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In a message dated 97-08-24 03:26:58 EDT, you write:

<< 2. Disregard interior partitions unless they are connected to the roof
 diaphragm for use to resist diaphragm movement (shearwalls). In most cases
 these do not add even a couple of pounds to the roof Dead Load. In addition
 to this where roof trusses are used, the interior partition stops at the
 bottom chord ceiling joist. Without a vertical strut at this location to
 push load to the roof, I can't see how the weight of the wall makes it to
 the diaphragm. >>

Dear Dennis;

So where do these loads go?
I have to disagree with you in this case. If you have wood trusses and the
walls
stop at the bottom of these trusses and there is a gypboard ceiling, then the
load 
will get into the ceiling and from the bottom of the wood trusses up to the
roof
diaph via diagonal members. If this is not happening then all our basic
engineering 
assumptions are wrong and these wall loads are either cantilevering from the
floor 
or some how disappearing. I will agree that the loads are not much, but lets
think 
for a second:

Big custom house with 12 feet high walls, min 2x6 framing and maybe even
plaster instead of drywall. Assume 1.7 psf for 2x6 and 2.8 psf for 5/8"
gypboard.
Total 7.3 psf. x 12/2=43.8plf x.183= 8 plf seismic load to roof and 16 plf to
floor
diaph. Do you still want to ignore this load? 
I am now really curious if I have been overly conservative all these years.?
Exterior walls with stucco is even more. 10 psf for 7/8" stucco+gyp+wood
framing
=14.5 psf not including insulation. I use 16 psf for exterior walls and 8 psf
for 2x4
interior walls. To make life easy I average out the partition load and use a
12 psf for
 the entire diaph. Then I do not have to worry about the load of the walls in
each
 direction and calculate the mass of each wall accurately at each level.

PS  I agree with you on all other issues you have raised.


Ara Maloyan P.E.