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wood posts & joists

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(sorry if this posts twice)

Wood Column Tables:
I have the complete set of the APA ASD books and I never remember seeing
tables for axial loaded members like AISC has, in terms of KL. I have seen
them in proprietary catalogs for glulam members. This is a pretty easy
solution once you set up a template in Mathcad or something similar, using
compressive stresses parallel to grain from APA, along with the proper KL
and all the other factors and formulas. If you are going to do any wood
engineering design I would reccomend ordering that complete package from APA
and have a good wood text book on hand, I use and like my college book,
"Design of Wood Structures" 3rd Ed by Breyer. With those two sets of refs
you can design most wood structures. I forgot the resident APA expert on the
SEA list, but I am sure he will chime in soon, he knows his stuff.

I don't think most of the residential and park deck and dock structures you
see are built according to any engineered design. Most are built by
carpenters and contractors who base their designs on experience, books and
manuals, and other empirical methods. We have done some engineered designs
for parks and many times they ask us to match the existing. I do the calcs
and they are way over built. I have a project right now for a park for a 6ft
wide deck, with 8ft spans, and they used 8.5" diameter piles!!! I am not too
worried about failure in compression or buckling of the piles, but I will do
the check if for nothing else for my own entertainment to see what their
allowable capacity actually is. To illustrate my point I ran a quick calc on
a S. Pine 4x4 , unbraced length = 5ft, the Pallow=13800+ lb! Try to load up
a deck post with that. You would need 10ft worth of lag screws to make the
connection work. Your stringers will control the design, or your
connections, not your posts (unless you are really high off the ground).

For deck design, the thing to worrry about is deflection (and probably
connections and hand rails). You do not want a bouncy or "spongey" feel to
your deck. Good luck finding a reasonable criteria from a reference for this
though. I built a wood walkway at my house and spaced the supports about
20", 2x6 decking simply supported. I have stood on one board and jumped up
and down and felt no give at all, and I weigh 245lbs. This is not scientific
, but try to determine on paper if 1/10" of deflection is ok for a deck.
Rules of thumb may say 16" o.c but this is way too small, I think. 20-24"
seems fine for comfort levels. USE SCREWS for the decking, this will stiffen
it up and you won't have nail heads popping out after a few years. Some wood
adhesive (comes in a caulking container) is another good addition for any
connections, especially decking.

Wood Joists Cantilevering off wall:

Call the manufacturer's engineer, they will need to solve that for you (or
be involved as a part of the solution) and are usually happy to do so. Not
that you cannot do it, but they have a pre-engineered product that can have
some unusual properties you may/may not be aware of, like shear,
concentrated loads, reverse bending, etc. They can run quick checks via
software and offer you typical details and such. It will be a time saver. I
have dealt with an engineer from TJI and he was extremely helpful.


Just my humble opinions...

Andrew Kester, EI
Longwood, FL




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