Which is Better: Plate Placement Method or Tooth Count Method?

To answer the question of which is the better method, we should start with a little background. A critical plate is a plate with a Joint Stress Index of 80% or greater. The ANSI/TPI 1–2014 Standard stipulates that critical plate inspections must be conducted when completing the three inspections per station/per shift/per week requirement. On average, the standard requires one critical inspection for each inspection made that week. Because some trusses will not have any critical plates though, several additional inspections will need to be made on the other trusses with multiple critical plates. For more on the process, see my previous article, “How Should Defects Be Recorded When Inspecting a Critical Plate?”

The critical plate inspection can be performed using the Plate Placement Method (PPM). The PPM is a tool that speeds this examination by generating a template within the truss design software used to design the component. In lieu of PPM, an old-school method, the Tooth Count Method (TCM), can be employed by counting and recording teeth and comparing “good teeth,” teeth that are installed effectively, and “bad teeth,” those teeth that are pressed in defect areas or are damaged to the extent that the tooth is ineffective.

So which method of recording critical plate information is better? Let’s compare them in a little more detail.

PPM – Plate Placement Method

There are three distinct elements in capturing data using the PPM. Recording defects is the most recognizable portion but there are two other elements. My previous article, “How Important is Angulation? Why is It Important?”, has additional information relating to angulation and center of connector within the computer-generated polygon. Here we will just acknowledge these because they are required essentially in both analyses.

Recording defects is one aspect of using the PPM. During the inspection, defects need to be recorded to provide historical data. One example is a knot defect recorded as a percentage of the defect circle. The template is placed over the defect and, using a marker, the profile of the defect is recorded within the circle on the PPM paperwork. The shading can be used to emphasize this condition. After the defect is recorded, a determination is made as to the percentage, so this information can be recorded into other databases.

Another defect example could be recording of folded teeth. Rectangles represent the area of the set of teeth that are damaged. Folded teeth are always recorded in pairs because it is assumed the opposing tooth, although not visible, is folded under the plate too.

A third situation would be recording the wane of the lumber in the plated area. The wane would be recorded like the knot defect and the area would be pieced and reflected in the defect circle.

And remember, you’re not recording defects simply because you need to check off that task on your list. You’re recording defects so that you can provide the reviewer of the report with information that helps them understand the nature and specifics of the defect. This analysis can be shared with the builders, supervisors, and managers too. While photos can be effective, they often don’t reveal the true nature of the defect, so this process is the best way to pass along this detailed information after an inspection.

TCM – Tooth Count Method

Using the tooth count method to record defects means we simply count teeth. The QC software generates the number of required teeth for each connector and each member. For example, the photo shows both the tooth count requirement and the PPM requirement. [For photo, See PDF or View in Full Issue.] To comply with the ANSI/TPI 1 requirements of Critical Plate Inspection, we need to record the number of teeth available that are good and then subtract the number of teeth that are considered ineffective which results in a difference. This difference is compared to the number of required teeth. If the number of required teeth is greater than the effective teeth, then the plate fails. Keep in mind that the plate also must comply with the angulation requirement, and to meet the tooth count method they must also be positioned as to provide the necessary coverage and transfer of forces.

So which method is better?

As shown in the chart, neither method is better in all situations. In fact, the side-by-side comparison shows that both methods have their benefits. The great thing is that they can be used interchangeably to suit conditions. Most software providers can provide the data and information on the same output with little difficulty. So our question can be rephrased – rather than asking which method is better overall, we should ask which is the better method to use for each inspection. You can be the judge of that!

An ANSI/TPI 1 3rd Party Quality Assurance Authorized Agent covering the Southeastern United States, Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. Glenn serves as a trainer-evaluator-auditor covering sales, design, PM, QA, customer service, and production elements of the truss industry. He also provides project management specifically pertaining to structural building components, including on-site inspections and ANSI/TPI 1 compliance assessments. Glenn provides new plant and retrofit designs, equipment evaluations, ROI, capacity analysis, and CPM analysis.