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# Wood connector allowable values

• To: seaint(--nospam--at)seaint.org
• Subject: Wood connector allowable values
• From: NRoselund(--nospam--at)aol.com
• Date: Thu, 10 Sep 1998 23:37:52 EDT

```I often calculate wood connection allowable values using the formulas of
Division III of Chapter 23 of the 1994 UBC; I've entered many of the formuals
for bolts, lags and wood screws into Mathcad worksheets.

I try to make sense of the results before applying them to a project, and find
that some of the Code formuals defy my attempts to give them intuitive
meaning.  A function of a variable raised to the power of another variable in
the denominator gets me completely boggled.  So I hope the folks who developed
the formula were smarter than me and I just try to at least make some sense of
the results.

One example is the group action factor Cg of Section 2335.5.6.  One of my
often-used details is a bolted wood drag strut splice.  Intuitively, I say
that the greater the spacing for the bolts, the less likely is splitting of a
drag-strut member when highly loaded in tension.  On that basis, I'm used to
using long splices and 6" to 8", or even 12" bolt spacings rather than the
minimum 4 diameter spacings.  The formula for Cg does not confirm my
intuition.  For example, for 8 3/4" diameter bolts in a line, for example, the
bolts at 3" spacings have allowable values of 14% and 22% greater than bolts
at 6" and 8" spacing, respectively.  Would I really be doing a better design
job with shorter splices?  Or how about clusters of bolts at 3" spacing at
each end of a long splice?

I have read in the NDS commentary, that the formula is taking into account
non-uniform loading of connectors in a row, but I'm still skeptical.  I'm
visualizing, for another example, a mudsill bolted to a foundation with bolts
at 32", or 48", or whatever spacing is appropriate for the load to be
transfered into the foundation at a shear wall.  Calculated with Cg, 3/4"
diameter bolts at 32" have about 60% of the capacity that the Code allows if
computed as individual bolts.  Does anyone use Cg for calculating mudsill
anchor bolts?  Should we?

What can someone say to relieve my skepticism?  Buddy Showalter, are you
there?

Another mudsill matter: several years ago, the SEAOSC Existing Building
Committee had a subcommittee working on techniques to retrofit mudsill anchors
in existing weak concrete.  We found that pretty crumby concrete (concrete
that you can't tighten a wedge-anchor into) can develop the strength of a 1/2"
diameter anchor bolt in a 2x4 mudsill.  We also found that at high loads, an
anchor bolt being bent over by a displacing mudsill splits the mudsill by
cutting into it on the side opposite the load.  We found that a square plate
washer was very effecting in preventing that kind of damage.  Bill Walker of
Simpson participated in the tests, and soon after, Simpson began selling their
BP series of plates.  Now, I always require a BP-type plate on all of the
bolted wood connections that I design for seismic forces.  I'm sure, based on
what I saw, that they will have greater capacities than bolts with a standard
cut washer, but I use the Code values, figuring we're getting better seismic
response at small extra cost.  But, It would be good to know how to use the
BP-type plates efficiently.  Are there any values, or any testing going on,
for bolted-wood connections using steel plates instead of cut washers between
the head or nut and the wood?

Nels Roselund
Structural Engineer

```