Quality Control

Digital QC: An Overview of the Digital QC Concept and Project Status

Truss in-plant QC and third party quality assurance is necessary to ensure that the finished product leaving the plant meets all building code requirements. The typical process, as it functions today, takes time and can slow down production. This webinar will discuss the development of SBCA’s Digital QC tool and much more.

In the SBCA booth at BCMC 2018, SBCA staff member Joe Schauer displayed how the SBCA Quality Control (QC) Committee’s initiative is a giant step forward in the area of component manufacturing QC.

Quality control (QC) is often thought of as an effort to catch mistakes made by production. However, many times problems and solutions extend beyond just the manufacturing process. 

Testing is underway to determine the effects of weather exposure and time on trusses.

Lumber Design Values

No matter the species, component manufacturers (CMs) purchase and rely on the accuracy and reliability of many different lumber design properties, including: bending (Fb); shear parallel to grain (Fv), compression perpendicular to grain (Fc^), compression parallel to grain (Fc), tension parallel to grain (Ft), and modulus of elasticity (E and Emin).

My framers are always complaining that the “trusses are bad.” I am looking for tolerance information that not only addresses the allowable variance in length and height, but also allowable variation in the top chord with regard to straightness (i.e. how straight should a pull string line from the top and bottom of top chord be?). Also, if trusses are set on a perfectly level wall, what variation is allowed from truss to truss (i.e. if I put a 10 ft. straight edge perpendicular to the trusses, how much can they vary in height, not just at peak or bottom but all along the top chord)?

The grading rules usually permit some percentage of visually graded lumber to be below grade – I believe it is 5%. ANSI/TPI 1 requires that all lumber used in trusses be of the grade specified by the truss design. A strict interpretation of ANSI/TPI 1 would require that the fabricator cull the 5% that is off grade. What are your thoughts on this?

If you have the condition where you are out by the max tolerances of 1/2 in., how do you correct the situation? Do you shim the truss from the bottom? Shim from the top? I will assume you do not shave the truss off. What is the published corrective action for situations that cannot handle the variation in truss height?

If the truss design drawing specifies using 2x4 1650F SPF, can 2x4 No. 2 southern pine be used instead? What are some things that need to be checked?

IBC 2012/2015 2303.4.6 and IBC 2012/2015 2303.4.7 state: 
2303.4.6 TPI 1 specifications. In addition to Sections 2303.4.1 through 2303.4.5, the design, manufacture and quality assurance of metal-plate-connected wood trusses shall be in accordance with TPI 1. Job-site inspections shall be in compliance with Section 110.4, as applicable.