When completing an in-house inspection, a critical plate inspection is required for each truss inspected. This requirement is from ANSI/TPI 1–2014. Specifically, per section 3.7.1:
No less than one critical joint per Truss selected for inspection, on average across all operational set-up locations at the Truss manufacturing facility, shall be inspected. Critical joints have a joint stress index (JSI), as defined in Section 8.11.3, greater than or equal to 0.80.
For the considerations needed when selecting which joints to inspect, see my May 2019 article, How Do I Choose Which Plates for a Critical Plate Inspection?. After those decisions are made, it’s very important to have the proper paperwork or digital information available to complete the critical plate inspection.
When doing the plate placement method (PPM) critical plate inspection, there are three different elements that need to be assessed and recorded for each face of the truss for each critical plate inspection:
- Angulation of the connector plate,
- Defects in the plated area, and
- The location of the center of the connector in relation to the “polygon.”
Recently, at several locations using various plate suppliers, I witnessed clients using the software-generated PPM paperwork without the polygon information. Figure 1 shows an example of PPM paperwork generated without a polygon. [For all images, See PDF or View in Full Issue.]
Because the software was not generating the polygon, the in-house inspector was assuming the plate could not deviate from the center shown. In each plant, we investigated why. The answer in each situation was due to settings within the software. For all major plate manufacturers, several switches must be “on” to generate the information. Figure 2 shows the setting within the Alpine software.
When the toggle is unchecked, the joint detail will not generate a polygon. The software is designed this way because generating this information increases the amount of runtime for the software. The software is not only designing the joint, but it’s also looking at the limits of potential locations and generating almost an infinite number of possible solutions.
After the settings have been set to generate the polygon, then the software will generate the third element. This is the step that provides the information required for the inspector, and this is the step that allows greater flexibility in plate positioning. Figure 3 shows the same joint as in Figure 1, but this time it has all of the information needed for assembly and inspection.
The Bottom Line
If your PPM-generated output does not show polygons, then check your settings. The information is readily available in your system, so it’s important that you access it. Do not assume that a plate cannot be shifted – that false assumption will make assembly very difficult, if not impossible.
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.