It is common
in wood frame and post and beam construction to use multiple pieces of
Dimension Lumber (`2 by’) material, nailed laminated to one another, to make up
posts and columns. Properly fastened
together, typically by nails, but sometimes by bolts, the resulting piece acts
(nearly) the same as a solid wood section of similar dimensions. This article deals with the `properly’
part. The

*National Design Specification for Wood Construction*(NDS), Section 15.3.3, gives us the prescription for nailing the pieces together. I summarize the prescription (rules) as follows:
1. adjacent nails are to be driven from opposite
sides of the post or column;

2. all nails must penetrate all the pieces
(plies, or laminations) and at least three-fourths into the outermost
lamination;

4. nails in a row must be spaced not closer than
20 nail diameters apart and not farther than six times the thickness of the
thinnest of the plies;

5. rows of nails must be spaced between 10 and
20 diameters apart;

6. nails must be located between 5 and 20
diameters from the edges of the column; and

7. two more rows must be provided where the wide
face dimension of the `lams’ exceeds three times the thickness of the thinnest
piece.

To
illustrate the above let’s consider a 3-ply 2 x 6 `column’; and let’s come up
with a nailing pattern for such a column that is 8 feet tall. I will `attack’ these rules in a different order
than given (but one that makes better sense to me).

First, do we
need more than one row of nails (item 5)?
2 x 6 Dimension Lumber is actually 1-1/2 inch (in.) x 5-1/2 in. The 5-1/2 in. wide faces will be nail
laminated to one another. All three pieces
have a thickness of 1-1/2 in., also being the minimum of the three. So, in `formula form’:

... (is) d > 3 t

_{min}? ...
or, in our
case, ... (is) 5-1/2 in. > (3)(1-1/2 in.) = 4-1/2 in.? Yes; we need more than one row of nails. Let’s try

__two rows__.
Second,
let’s come up with the required nail length.
Three plies of 1-1/2 in. each will give a total thickness of 4-1/2
in. The nails must

*be at least long enough*to penetrate three-fourths of the last lam, or,
So, I need
nails that are at least 4-1/8 in. long, ideally about 4-1/2 in. long, and they
can be even longer, but I must then clinch them (pound over the protruding tips).

In `formula form’,

L

_{min}= [(n-1) + 0.75] x t,
n is the
number of plies and t is the thickness of the plies, in this case assumed to
all be the same.

Choosing a
nail size ... the `30d’ common wire nail has a length of 4-1/2 in. and diameter
(D) of 0.207 in. (NDS Table L4).

Perfect!
(with regard to length).

Now to deal
with the end distance:

In formula
form,

or, in our
case, 15 (.207) = 3.1 in. ≤ end distance ≤ 18 (.207) = 3.7 in.

Let’s pick

__end distance = 3-1/2 in.___{min}= 6 x 1.5 in. = 9 in.

Let’s pick

__spacing of nails in a row = 9 in.__
For row
spacing:

... 10 D = 10(.207) = 2.1 in. ≤ row spacing ≤
20 D = 4.1 in.

Let’s

*3 in., and assume only two rows.*__try__
This leaves
us with edge distances of, assuming things centered, ...

5-1/2 – 3 =
2-1/2 ... divided by 2 = 1-1/4 available each edge.

The edge
distance requirement is:

... 5D = 5 (.207) = 1 in. ≤ edge dist. ≤ 20 D
= 4.1 in.

So, yeah,
let’s

__space the rows 3 in. apart and provide at least 1 in. edge distance__. Two rows works perfectly.
Summarizing:

Two rows of
30d common wire nails; 9 in. (max.) o.c. each row, rows spaced 3 in. apart and
not closer than 1.0 in from edges; first and last nails of each row 3-1/2 in.
from ends.

References

National
Design Specification for Wood Construction, American Wood Council, Washington,
D.C.

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