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Re: nailing zones in plywood diaphragms

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Tom Jakoby wrote:

. > Roger Turk wrote:
. > >I don't see why changing the nailing zones of diaphragms would be any 
. > >different than what is done in changing the spacing of stirrups in 
. > concrete, >or stiffeners in built-up girders, or discontinuing 
. > reinforcing steel, or >changing cover plate sizes.  You take the closer 
. > spacing/greater capacity >requirements out **beyond** the point where 
. > larger spacing/less capacity >becomes adequate, and repeat as necessary.

. > I agree the transition should be made beyond where the higher capacity is 
. > required.  

I'm afraid that you misunderstood what I wrote.  The transition is made 
beyond where the nailing with the **lower** capacity is adequate.

. > It is NOT absurd to space nails differently on one side of a plywood 
. > joint than on the other!  This is exactly where the transition should 
. > take place.  If not there, then where? 

Since the nailing with the larger nail spacing (lower capacity) is already 
more than adequate (if it isn't, it *should* be) for the shear force at the 
transition location, why have two different nail spacings on each side of a 
plywood joint?  As for your question, "If not there, then where?", what is 
wrong with having the transition location between 
joists/purlins/girders/plywood joints?  In fact, with staggered end joints, 
you will not have adjacent panels ending at the same location anyway.

If you superimpose your capacity diagrams over your shear diagrams, you will 
(should) find that your capacity lines are always greater than your shear 
values, and at the transition location the capacity line for nailing at 
closer spacing is **much** greater than the shear at that location and the 
capacity line for nailing at the larger spacing is greater, if only slightly 
greater, than the shear at that location.  Therefore, only nailing at the 
larger spacing would be necessary at the transition location.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona