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# Anchor bolt design - wood sill on concrete

• To: <seaint(--nospam--at)seaint.org>
• Subject: Anchor bolt design - wood sill on concrete
• From: <awcinfo(--nospam--at)afandpa.org>
• Date: Tue, 02 Oct 2001 10:52:54 -0400

```Dennis,

I've probably missed your deadline since i get the digest, but here's some info.
that might help for future reference. The method you describe was part of 1991
and earlier editions of the NDS (section 8.2.3) which was probably transcribed
into the 1997 UBC (sorry i don't know the specific section). With this method
one assumes the main member (concrete) to be twice the thickness of the side
member (t_m = 2t_s) and use the dowel bearing strength of the side member for
both (Fem=Fes). Note that using the wood dowel bearing strength perpendicular to
grain for concrete would be very conservative, so an interpretation was
developed by AF&PA in 1995 as follows:

"There have also been requests regarding interpretation of NDS 8.2.3 for
wood-to-concrete connections. Specifically, designers want to know if NDS Table
8.2A can be used with the appropriate variables to determine design values for
anchor bolts. NDS Commentary section 8.2.3 specifically states:

"To determine the allowable bolt design value for such a connection, the yield
mode equations of 8.2.1 can be entered with t_m equal to twice t_s and Fem equal
to Fes; or the design values from Table 8.2A or 8.2B for the applicable main and
side member relative thickness and bolt diameter can be used.

"For perpendicular to grain applications, a literal interpretation of NDS 8.2.3
would suggest that the perpendicular to grain Fes value be used for Fem. As you
can see from the attached Table 8.2A, this would result in a very conservative
Zperp value. The interpretation offered by AWC's engineering staff is that
Zsperp values from NDS Table 8.2A can  be used for this application. So Fem
would actually be the parallel to grain dowel bearing strength for this case.
This interpretation is consistent with research of wood-to-concrete connections
that AWC's Technical Committees are evaluating for possible inclusion in the
1997 NDS."

The 1997 NDS (section 8.2.3) actually codifies a dowel bearing strength for
concrete of 6000 psi for concrete with a compressive strength of 2000psi or
greater (NDS Table 8.2E, footnote 3). There are also pre-calculated values in
NDS Table 8.2E for 1.5", 2.5", and 3.5" side members, for various species loaded
both parallel and perpendicular to grain.

HTH

Buddy Showalter, P.E.
AF&PA/AWC

From: Structuralist [mailto:dennis.wish(--nospam--at)gte.net]
Sent: Monday, October 01, 2001 6:14 PM
To: seaint(--nospam--at)seaint.org
Subject: Anchor bolt design - wood sill on concrete

I am going nuts - It's been a long time since I manually designed my sill
anchors and I remember a section of the code that clearly indicated a method
something like 1/2 the value of twice the thickness etc. etc.  (so for a
1-1/2" sill you are looking for anchor bolt values for 2-inch and 4-inch
members - since twice the 1-1/2 inch member is 3" and between the table
values) or something like this. I can not find it in the code. It may be
that I am stressed out trying to make a promised deadline, but I've gone
brain dead and cant find the paragraph in the code that explains the
procedure.
Can someone guide this mentally blinded engineer to the appropriate code
section????  I've just wasted the last hour looking back through old codes
as well as current codes and am beginning to think that I must have dreamed
the whole thing:?)

You will have my eternal gratitude!!!!

Dennis S. Wish, PE
Structural Engineering Consultant
structures(--nospam--at)engineer.com
760.564.0884 - Phone
208.361.5447 - Efax

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