Sometimes it is necessary to deviate from the truss design drawing and use a different connector. This may happen when a specific size connector is not available or when the original connector has been removed.
Per ANSI/TPI 1 Section 3.6.3, a metal connector can be substituted if the new connector is a larger size or equal size in both dimensions. If an installed connector has been removed, an evaluation of the used area needs to be conducted to determine if the plate size needs to be increased. For more information on this process, see my previous articles Is There a Reduction for Plating in a Previously Plated Area? (May 2016) and Are You Removing the Connectors Carefully When Replacing Them? (November 2022).
When upsizing, it’s important to know that you cannot substitute a connector that is not of the same style or gauge. For example, replacing a 3×9 20-gauge plate with a 3×9 20-gauge high strength or 16-gauge high strength connector is not allowed unilaterally without specific engineering design. The connector might work, but it might not. The connector design dictates the number of teeth and the gauge impacts the load capacity by increasing the cross section, which is the area of the connector that transfers the load through the connector. The number of teeth is critical to the load transfer into the wood member. For example, consider the MiTek connector plates shown: Figure 1 is a standard 20-gauge connector, Figure 2 is a high strength 20-gauge connector, and Figure 3 is a high strength 16-gauge connector. Note that each one has a different tooth configuration, and that means each one will have a different number of teeth in a specific design. The images are of MiTek connectors, but this is true with all brands. Likewise, brands are not interchangeable without specific engineering. (For more on that topic, see my March 2021 article, Can a Fabricator Mix or Substitute Connector Plates From Different Manufacturers?.) [For all images, See PDF or View in Full Issue.]
Another often misunderstood aspect of upsizing connectors involves the change in size. When a larger connector is used, the profile of the component may change the plate position dramatically. For example, Figure 4 shows the original connector placement in black and the new position of a larger connector in red. Quite frankly, this is not allowed and will require additional evaluation because of ANSI/TPI 1 Section 3.6.5. The plate must have the same orientation and entirely cover the area footprint of the original connector design. Furthermore, the replacement connector cannot impact other design aspects or functionality of the truss.
Remember to Follow the Rules
If you are attempting to upsize a connector without specific engineering, then these rules must be followed:
- The plate must be of the same manufacturer as specified by the design.
- The size must be equal to or greater than the original design in both dimensions.
- The plate must be of the same style.
- The plate must be positioned over the entire original plated area.
- The plate cannot change the functionality of the truss.
- The plate cannot extend beyond the profile of the truss.
- If the plate is a replacement of a removed connector, then an increase in size may be required to cover the entire used area.
Yes, a change can be made while manufacturing the component—but only if you follow the rules and keep in mind that additional engineering may be necessary. When in doubt, remember that you can always take the time to rerun the truss with the new design.
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.