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RE: Anchor bolt design - wood sill on concrete

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The 1991 NDS is the standard incorporated in both the 1997 UBC and the 1998
California Building Code (based on 1997 UBC).  Thus, eventhough the 1997 NDS
has revised rules, they are not necessarily "code compliant" in UBC
territory unless you can convince the building official that it is a
nationally approved standard [which shouldn't be too hard with most
enlightened building officials  :<) With the others ...? ]

Regards,
Bill Cain, SE
Oakland CA

-----Original Message-----
From: awcinfo(--nospam--at)afandpa.org [mailto:awcinfo(--nospam--at)afandpa.org]
Sent: Tuesday, October 02, 2001 7:53 AM
To: seaint(--nospam--at)seaint.org
Subject: Anchor bolt design - wood sill on concrete


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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