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August 2023 #15289 Page #35
Why is the Gaps Limitation So Important to Truss Fabrication? NSI/TPI 1 is a practical guide to manufacturing metal plate connected wood truss. It considers rational expectations and By Glenn Traylor reasonable manufacturing capabilities that help ensure a sound product. Due to the nature of wood, cutting equipment and processes gaps do occur. These gaps can cause deflection. This can occur over time. Due to labor cost and waste involved, eliminating all gaps can be expensive and not cost effective.
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So, which gaps are permissible, or not? Shown is an excerpt from the ANSI/TPI 1 standard, Figure 3.7-4 Wood Member to Wood Member Gaps.
In this diagram, the areas denoted in red illustrate allowable gaps.
Assumptions Determining if a gap is acceptable relies on a few assumptions:
1. The design software assumes that joints are in contact with each other. 2. Connectors are not designed to prevent buckling when presented with a compressive force. 3. Forces in tension are not subject to buckling but the forces can reverse due to variations in load cases. An example of force reversal would be wind uplift on a normal gravity load. Continued next page
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