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June 2021 #13263 Page #41
Can Designs Be Modified During Truss Manufacture? By Glenn Traylor
T
he simple answer to the title question, can designs be changed during manufacturing, is yes. But, the situation is rarely straightforward and simple in reality. The better question is: What considerations are necessary when making modifications to the design while manufacturing a truss? To answer the broader question, the answers stack up as follows. First, designs can be modified if there is engineering to back up the change and it is documented. Second, as we build product there are adjustments that we can make to accommodate for the defects of the materials we are using. Third, the lumber should be to grade and all the rules in ANSI/TPI 1 should be followed. Wane and other defects that impact tooth holding can force adjustments to the design. If these defects are within acceptable parameters during fabrication, they can be made and still meet the code requirements. A simple example might be upsizing a connector for excessive wane in the plated area. Larger plates also may be used due to limits of inventory, upsizing for handling, or simplification of plate picking. To understand the big picture though, it can be helpful to consider specific situations. The first picture brings into focus the question of what can we do when we have a broken web or chord? Why can’t we simply put a plate over the damage like this photo illustrates? If we had a specific sealed engineering design, we could make this repair. The problem is that such a repair typically is not worth the time, cost, and effort required to document the damage, initiate the repair, deliver the repair directions to the shop, and then track the documentation connecting it with the project. For this reason, repairs of broken webs and chords are not allowed and should never be done unless there is that specific design.
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