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.
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 the PPM, an old school method 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 point the tooth is ineffective.
Recording defects is one aspect of using the PPM. During the inspection, defects need to be recorded to provide historical data. In example “a” shown in the figure [see PDF or view in full issue], a knot defect is recorded as a percentage of the defect circle. While this clearly records the defect situation, it doesn’t provide the reviewer with enough information to know the actual defect situation. In contrast, example “b” shows the same defect, and it is recorded correctly. 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.
Example “c” shows an incorrect recording of folded teeth; example “d” is the correct way to record this information. The 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.
Another situation (not shown in the figure) is recording the wane of the lumber in the plated area. The wane would be recorded similar to the knot defect shown in “b,” that is, 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.
Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. While he is a TPI 3rd Party In-Plant Quality Assurance Authorized Agent covering the Southeastern United States and performs 3rd party safety auditor services, these articles represent his personal views, knowledge, and experience. 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.