Wednesday, January 23, 2008

FW: 3x3 square sill plate washers

There are no special size requirements in the 2006 IBC where bottom plates get larger. See below for a summary of 2006 IBC and AF&PA 2005 Wind & Seismic Standard.

2006 IBC Section 2305.3.11 follows:

2305.3.11 Sill plate size and anchorage in Seismic Design
Category D, E or F. Anchor bolts for shear walls shall
include steel plate washers, a minimum of 0.229 inch by 3
inches by 3 inches (5.82 mm by 76 mm by 76 mm) in size,
between the sill plate and nut. The hole in the platewasher is
permitted to be diagonally slotted with a width of up to 3/16
inch (4.76 mm) larger than the bolt diameter and a slot
length not to exceed 13/4 inches (44 mm), provided a standard
cut washer is placed between the plate washer and the
nut. Sill plates resisting a design load greater than 490 plf
(7154 N/m) using load and resistance factor design or 350
plf (5110 N/m) using allowable stress design shall not be
less than a 3-inch (76 mm) nominal member. Where a single
3- inch (76 mm) nominal sill plate is used, 2- 20d box end
nails shall be substituted for 2-16d common end nails found
in line 8 of Table 2304.9.1.

Exception: In shear walls where the design load is
greater than 490 plf (7151 N/m) but less than 840 plf (12
264 N/m) using load and resistance factor design or
greater than 350 plf (5110 N/m) but less than 600 plf
(8760 N/m) using allowable stress design, the sill plate is
permitted to be a 2-inch (51 mm) nominal member if the
sill plate is anchored by two times the number of bolts
required by design and 0.229-inch by 3-inch by 3-inch
(5.82mm by 76mm by 76mm)platewashers are used.

Note that there is no requirement for a bigger plate washer as the bottom plate increases from 4" nominal width to 6" nominal width. Also, it is important to note that a 3" nominal thick member is needed where ASD shears exceed 350 plf unless the bottom plate is anchored with twice the number of anchor bolts required by design as noted in the Exception. All of these special requirements apply only in SDC D, E, or F.

2005 AF&PA Wind & Seismic Standard

2006 IBC Section 2305.1 permits use of AF&PA's 2005 Special Design Provisions for Wind & Seismic (Wind & Seismic) as an alternative to provisions of 2305. Foundation anchorage requirements are covered in as follows: Anchor Bolts: Foundation anchor bolts
shall have a steel plate washer under each nut not less
than 2-½" x 2-½" x ¼". The plate washer shall extend
to within ½" of the edge of the bottom plate on the
sheathed side.

The difference in Wind & Seismic-05 washer size (2-1/2" square versus 3") is a minor issue based on results of recent testing. A ½" distance from edge of washer to the sheathed edge of the bottom plate is specified and is intended to limit amount of cross grain bending induced in the bottom plate as the shear wall is racked. Wind & Seismic-05 Commentary C4. specifically addresses use of bigger plate washers and plate washer location for cases where bottom plate width exceed 4" nominal width:

C4. Anchor Bolts: Plate washer size and location
are specified for anchoring of wall bottom plates to
minimize potential for cross-grain bending failure in the
bottom plate. For a 2-1/2" x 2-1/2" plate washer centered
on the wide face of a 2x4 bottom plate, edges of the plate
washer are within 1/2" of both edges of the wall. For wider
bottom plates, such as 2x6, a larger plate washer may be
used so that the edge of the plate washer extends to within
1/2" of the sheathed side, or alternatively, the anchor bolt
can be located such that the 2-1/2" x 2-1/2" plate washer
extends to with 1/2" of the sheathed side of the wall.

Hope this information helps.


John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

The guidance provided herein is not a formal interpretation of any AF&PA standard. Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.

From: "Pinyon Engineering" <>
To: <>
Subject: 3x3 square sill plate washers
with the new 2006 IBC square plate washer requirement for shear wall = sill plates-=20 I have a question - In the Dec 2007 ICC building Saftey Journal = publication - on page 16 they show a 2x4 plate and how to place the = washer with the slotted hole. what if I use a 2x6 plate to get the same = coverage of the plate do I need a 5x5 washer? It seems the tolerance = for the washer placement is within 1/4" of the back of the shear panel. = (what about 2 sided shear walls?) what should I put on my plans to teach = the contactors how to do this? or to teach me how it should be done. Thank, Tim Rudolph Pinyon Engineering Bishop, CA

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