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Component Manufacturing dverti$er
Don’t Forget! You Saw it in the
Adverti$er
May 2019 #11238 Page #36
How Do I Choose Which Plates for a Critical Plate Inspection?
T
he requirement is: an inspector will, on average, inspect one critical plate for every inspection made during a week. That requirement is the baseline number for the quantity of critical inspections to perform—but because some trusses do not have critical plates, it’s necessary to inspect several extra critical plates. A critical plate is one that meets the critical potential of 0.80 or 80% of plate capacity related to the Joint Stress Index (JSI). Just as some trusses may not have any critical plates, other trusses may have many. So the question becomes: what considerations should we use in deciding which critical plate to inspect when there are an abundance of choices? Normally, the inspector would consider the plates with the highest JSI. Another consideration is identifying the plates which are most likely to be in error. Also factoring into this decision is consideration of which plates are the most difficult to have placed correctly.
The photos show various critical plates. Comparing many inspections, the most likely mistakes are on the most complicated joints—those with many members. Another common mistake is to shift a plate centered on the joint when it’s the splice that needs the connection. Often times, it’s the peak plate of a scissors truss when the top chords are 2 x 6 or wider. The builder confuses the joints design, trying to tie the two chords together, neglecting the consideration for tooth holding in the king post. Sometimes the simple joints should be inspected, such as a simple splice. They can be critical at 100%— but the clearly-indicated location is always centered on the joint, so it should be a simple training procedure to get builders to understand these positions. Of course, the truss drawings have offset dimensions and lasers and ink jet printing give exact locations—but even with these tools, these joints are sometimes plated wrong and should be part of an inspection. Continued next page PHONE: 800-289-5627
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