The 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 [see PDF or View in Full Issue] 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.
In fact, it can be helpful for an inspector to develop a list of “watches” that includes those connections which are often wrong for the particular facility. The inspector can have a mental list of problem joints to watch for during the check.
So the bottom line is: inspectors have a choice when deciding which plates to inspect, and they should use both common sense and experience to make that decision. Inspections should be done for plates that are most likely to be wrong, without ignoring the others.
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.