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RE: 1997 NDS Equation Error?

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The NDS could solve this confusion by clarifying that only the values for
Zis, Ziiis, and Ziv apply to wood-to-concrete connections.

Mark T. Swingle, PE, SE


To give you all a heads-up on the direction the 2001NDS has gone for
connection design, you might want to review Technical Report 12 on the AWC
website more closely.

To summarize, all dowel-type connectors will be included in one chapter
(nails, wood screws, lag screws, bolts) with one set of yield equations
derived from the mechanics-based approach outlined in TR12 (don't worry,
we'll still provide tabulated values). For single shear connections, all 6
yield mode equations will need to be considered, regardless of the main and
side member material. however, if in your judgement as an engineer, you
determine that it's unnecessary to evaluate certain yield modes because you
know they won't control, that's your decision. I would liken this approach
to beam or joist design where you know that moment, shear, deflection, and
bearing all have to be considered, but with experience you determine for
certain cases shear never controls, so you just check the other cases. 

while intuitively, it may seem that mode Im or II will never control in a
wood-to-concrete connection, there may be cases where concrete or mortar
with lower compressive strengths are used, and those cases would need to be
evaluated. the yield theory provides that flexibility.

Hope this information helps.

Buddy Showalter, P.E.

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