New “Strong Axis” Floor Truss product

Rusk Component and Design is offering a new floor truss concept to replace an old standard. Currently, most truss companies are offering a standard floor truss manufactured in the “weak axis” direction of the 2x4 members. Basically, the top and bottom chords, as well as the webs are placed so the they are loaded in the flat direction or “weak axis”. This has been done to allow maximum pass through openings for plumbing, ductwork, etc. which works well in shorter spans.

As today’s spans are increasing to limit the amount of primary support members such as beams and posts, below, these “weak axis” floor trusses require more and more materials. Chords that are doubled, even tripled, tight web spacings, doubling some webs, and larger plates.

As an alternate, Rusk Component and Design is offering a new floor truss system, “strong axis” trusses. A strong axis floor truss is basically a roof truss configuration for a floor. These trusses can be fabricated so that the bearing end of the truss can “step” down from the bearing wall for example, reducing the intrusion into the lower roof ceiling space and using a 11 7/8 inch deep LSL rim in place of a 2x4 Flat Ribbon. The advantage to the Rim is any exterior deck connections now do not require extra framing for support. The Simpson Strong‐Tie SDW and SDS deck ledger details can be used in connection just like on an I‐Joist floor system.

With an 18 inch full truss depth, and an 11 7/8” top of wall depth, the minimal loos of ceiling height below as compared with a standard 11 7/8 inch deep I‐Joist system is:

• (a) At the Foundation Wall: 4 5/8”
• (b) At a Frame Wall: 6 1/8”

With the step down condition, and an 18 inch full depth, these trusses can make a maximum span of twenty feet (20 ft). A minimum open “chase” area of 36 inches x 11 inches can also be included. In addition, the web configuration can allow for a 8 inch diameter round duct to clear.

The Truss can also be a “2‐span” member over a flush steel beam such as a W8x24. This beam can be set so that bottom of steel beam can match bottom of truss allowing an 8 inch round duct to pass between trusses over the top of the beam for those hard to reach rooms.

These trusses can be spaced from 12 inches on center to 24 inches on center maintaining a clear space between trusses for ducts, plumbing, electrical, and other items that need to run parallel with the trusses.

• (a) At 12 inches on center clear distance between trusses is 10 1⁄2 inches.
• (b) At 16 inches on center clear distance between trusses is 14 1⁄2 inches.
• (c) At 24 inches on center clear distance between trusses is 22 1⁄2 inches.

We would recommend 16 inch spacing of russes with the use of 3⁄4 inch plywood floor sheathing. This gives a stiffer “feel” of the floor for the end user due to the deflection of the floor sheathing at greater spacing.

Below are some pictures of a “mock‐up” floor system Rusk component and Design has at its Turner Boulevard Facility. Feel free to call, or drop in to see it in person and ask any questions you may have. Rusk Component and Design looks forward to providing for your component needs.