The New FWANZ in the Simpson Strong-Tie Wood Construction Connectors 2009 Catalog

The new 2009-2010 Simpson Strong-Tie Wood Construction Connectors Catalog has some new items that are pretty cool, especially in regard to the design of residential construction. In this article I will focus on the FWANZ Foundation Wall Angle.

FWANZ Foundation Wall Angle

This connector (pages 4 and 25) of the Catalog is for connecting a foundation wall to a floor system, in particular a foundation wall resisting significant lateral force from backfill, say a basement wall. Prescriptive design of basement foundation walls assumes one-way action of the wall, the wall carrying the lateral forces up to the floor above and down to the basement slab. As such, we need a suitable load path for the forces to get into the floor above, and then the floor will act either as a diaphragm taking the loads to the sides, or as a big, flat, thin, compression member to the opposite wall. This connector nails to the mud sill (with 1-1/2 in. nails) and nails to the rim board. The previous version of this connector, the FWAZ is attached through the mud sill to the foundation wall with the Titen HD concrete lag screws, and is nailed to the rim. Thus, this new connector is installed independent of the mud sill anchorage; the flip side of this being the mud sill must still be anchored (now independently) to the foundation wall (with either cast-in-place or equivalent post-installed anchors).

As an example, consider the International Residential Code (IRC) Table R404.1(1) for a wall height of 8 ft and unbalanced backfill of 7 ft of silty-sand (SM). The Table indicates that the top reaction is 321.6 plf and that an angle must be provided at each joist that bolts to the joist/blocking and to the foundation wall through the mud sill.

Using the FWANZ with (8) 10dx1-1/2 nails to sill and (5) 10dx1-1/2 nails to rim, the allowable load is 945 lb to a 2 x rim (`90' column for a permanent load). Hence, these connectors may be spaced at ...

... s = spacing = 945 lb per connector / 321.6 plf = 2.9 ft per connector, or 35 in. per connector ...

... or ... if we have 16 in. joist spacing, let's go with 32 in. o.c. spacing (every other joist space).

The mud sill must be fastened to the foundation wall to resist this same reaction. Prescriptively we can determine the attachment with IRC Table R404.1(2). Same wall height, backfill, etc., gives ½ in. anchors @ 12 in. o.c., ... or ... 5/8 in. anchors @ 1.27 x 12 = 15 in. o.c. It would be really convenient if we could stretch this out to 16 in. o.c. ... and we can, if we `design' the connection using the NDS (National Design Specification for Wood Construction). (See the calculation ... here.)

This is pretty nice; instead of casting an anchor in place at each joist location and hoping to get it right next to the joist (following the Table R404.1(2) angle thing), we can place the anchors every other joist spaceconveniently in-between the joists. And now we just attach the joist prescriptively (say, per Table R602.3(1)) to the mud sill (with some nails).

This accomplished, the force has been transferred from concrete wall to mud sill, and from mud sill to rim joist. The force must be transferred from rim joist to floor sheathing via the boundary nailing and direct bearing against the ends of the joists or blocking.

In this example we can space the FWANZ at twice the earlier FWAZ (since the FWAZ spacing would be determined by the anchor bolt spacing).

NICE!

Sources or References

Simpson Strong-Tie, 5956 W. Las Positas Blvd., Pleasanton, CA 94588, www.strongtie.com.

International Residential Code, 2006, International Code Council, 4051 West Flossmoor Road, Country Club Hills, IL 60478.

National Design Specification for Wood Construction, 2006, American Forest & Paper Association / American Wood Council, 1111 Nineteenth St., NW, Suite 800, Washington, D.C., 20036, www.awc.org.

Stretching the 12 in. x 1.27 = 15 in. Spacing of 5/8 in. Anchors in Table R404.1(2) to 16 in., reinforced-concrete.blogspot.com.