Interesting unusual truss design

[Barry Adair]

Ripped this from TIJ

Don't be shocked if you come upon these during an inspection

http://www.turb-o-truss.co.za/index.html
http://roundendwebs.com/
http://www.turb-o-web.com/ElipIII.pdf

The following information should help you and your fellow inspectors regarding the quality criteria for metal-plate-connected wood trusses using round cut webs. The general use of round cut webs do work within the framework of the Truss Plate Institute's (TPI's) Quality Assurance Program. Around 2000, TPI's Technical Advisory Committee rendered an interpretation to the then metal-plate connected wood truss design standard ANSI/TPI 1-1995 Section 4.6.4 that the wood-to-wood joinery gap tolerances (maximum and average) applied only to cut to bear wood members, and were not intended for round cut web applications. However, as TPI began working through the revision process to ANSI/TPI 1-2002, there appeared to be a growing consensus to assign a small tolerance for wood-to-wood point contact tolerances using round cut webs. So, ANSI/TPI 1-2002 included the following language:

3.7.6 Wood Member-To-Member Gaps

3.7.6.1 Except as indicated in Section 3.7.6.2, maximum gaps in all joints except floor truss chord splices shall not exceed 1/8'', where the gap is measured at each edge of the metal connector plate for joints in which the plate edge is within the scarf, and measured at the end of the scarf for joints in which the plate edge is outside the scarf. Scarf is the portion of the joint in which it is intended that there be wood-to-wood contact between two wood members. The maximum gap for floor truss chord splices shall not exceed 1/16" across the entire scarf. For joints designed with single points of contact between adjacent members as shown on the Truss Design Drawing, the maximum gap between all contact points shall not exceed 1/8". (See Figure 3.7-3)



Figure 3.7-3 Wood Member-to-Wood Member Gaps

3.7.6.2 Where a metal connector plate is designed to carry all compression load at the joint without buckling of the plate steel section, the allowable gap shall be that amount of gap used in sizing the metal connector plate as specified on the truss design drawing by the Truss Designer.

What you are illustrating in your photos are a system of standardized webs with standard end cuts, and, in most cases standard ends and standard lengths. The reason for using these standardized webs is that they reducing web cutting labor, truss assembly time and web lumber. But there are reductions in the metal plate connector's design values when the webs are standardized. These are engineered and will handle the loads the trusses are designed for. You mentioned Turb-O-Webs as an example - Turb-O-Web trusses have been used in the United States since 1999. Specific questions regarding the Turb-O-Web System can be answered by calling them at 888-TURBOWEB.

Ryan Dexter, P.E.
Director of Technical Projects
WTCA - Representing the Structural Building Components Industry
6300 Enterprise Lane
Madison, WI 53719
rdexter@qualtim.com
608/310-6744 (direct)
608/213-1527 (cell)
608/274-4849x144
608/274-3329 (fax)
www.sbcindustry.com

[relliott]

What is this..DIY trusses?

[Barry Adair]

Originally Posted by relliott

What is this..DIY trusses?

Bob,
Try your other pair of glasses.

[relliott]

Saw an ad for a saw to cut them
Yeah that sarcasim comes from TIJ alright.