Planning Ahead: What Issues Should SBCRI Explore?

"What issues should SBCRI explore?" is the first question in a poll currently open to SBCA members. It was no surprise to Dave Motter, a member of the SBCA Industry Testing Subcommittee, that quality control and bracing were two of the top three responses. These are issues, he points out, that “have a very, very, very big impact on us as component manufacturers and on the industry.”

Members have responded to the poll so far saying they are interested in data showing what plate placement tolerances are necessary to ensure adequate truss performance. Members are also looking for testing data to demonstrate the need for good quality control practices and the consequences of poor manufacturing.

One important—and surprisingly tricky—quality issue of particular concern to members is how to determine the critical joints of a truss. Poll respondents pointed out that design specifications and testing data rarely agree on which joints of a truss are most essential to supporting the load of a structure. Developing a data set that can reliably indicate which joints are truly crucial to structural stability can help component manufacturers focus their quality standards and practices on the places that matter most.

Bracing, both temporary and permanent, is an issue of perennial importance to the industry. Members are especially interested in additional testing of long (60 foot or more) span trusses. Poll respondents wondered whether current temporary bracing spacing requirements, as outlined in BSCI documents, were more conservative than necessary. Everyone has witnessed more minimal bracing practices in the field that have not resulted in widespread failures, suggesting that a thorough investigation and a rigorous justification of recommended bracing practices could clear up confusion and promote safer, framer-friendly installation throughout the industry.

More unexpected than QC or bracing was the item that made the top of poll respondents’ priority list: multi-ply girder truss design. “That is a little surprising,” Motter admits. “As a component manufacturer, it’s a very low-cost item for us.” However, poll respondents were interested in the percentage of load transferred through ply-to-ply connections and on whether dense nailing patterns, like four rows of nails at four inches on center, are strictly necessary. As pointed out in one comment, having design values accurately reflect the load on individual plies in a girder is key to avoiding girder truss failures. In addition, this type of testing might provide a more definite answer as to how many plies are necessary to transfer a given load.

The poll, Motter says, “provides really good information and gives us a good idea of which direction to go moving forward.” The next step, he says, is writing test plans. “These are very broad topics,” Motter points out, “so what we need to do is drill down a little bit.”

The SBCA Industry Testing Subcom-mittee is currently working on test plans and will soon start considering test funding and scheduling. High on the list is bracing testing—it’s top-of-mind for SBCA members with the Truss Plate Institute’s truss bracing standard (TPI 3) nearing completion. Test data collected now could play a key role in verifying or improving the design methods that are being reviewed and updated.