The Development of the Truss Plate, Part II: Cal Jureit’s Invention

Issue #14278 - September 2022 | Page #10

By Joe Kannapell

Civil engineer Cal Jureit had moved on from wood structures to concrete foundations, but not completely. While he was engaged with the problem of building houses on Miami’s marshes near the Everglades, he had left the problem of wood connections unresolved. Perhaps his ongoing work on Dade County’s inaugural building code brought his unsatisfying truss connection work back to him. Or maybe his engineering instincts haunted him until he resolved this vexing problem. Nevertheless, two years after leaving wood design, his billion dollar idea for a nail-less truss connector came to him suddenly, while in church, and that was just the beginning. [For all photos and images, See PDF or View in Full Issue.]

After church, Jureit went into his garage and punched parallel rows of long nail-like projections from a piece of aluminum. Then, when he realized the nails were too close together and would probably split the wood, he secured opposite edges of the plate and pulled them apart, stretching the plate, and widening the slots to separate the teeth.

Jureit submitted the “stretched” design in his initial patent application just two months after his discovery, stating, “…said plate being expanded transverse of said slots to form substantially diamond shaped apertures.”

One year later, after much testing and study, Jureit concluded that he had found, “…marked improvements may be made if certain changes in the connector are made.” And his results, though less aesthetic, launched a whole new industry.

From a cross section shown on the later patent drawing, the tooth is depicted as being longer than half the width of the 1950’s 2x4 thickness. However, it has been angled from “6 to 20 degrees” so that nails on opposite faces of the lumber don’t collide. This would become a significant issue as lumber thicknesses were reduced to 1.5” around 1970.

Jureit devoted considerable groundbreaking research between the time of his discovery in July 1955 and his second patent application in September 1956. Evident from the detailed specifications in the text is that Jureit’s work involved load tests of dozens of custom fabricated truss plate configurations. For example, he notes, “I have found that nail length L in Figure 5 must be at least 6 times the thickness of the metal plate and should not be over approximately 17 times the metal thickness to withstand bending upon pressing. A length equal to approximately 12 times metal thickness has been found quite satisfactory.” Though he seems to be helping his competitors by revealing the results of his research, he also sought to broaden the range of the claims of this patent to exclude competitors. But these claims would soon be contested in court.

In summary, Jureit explored a wide range of options, but settled on a solid design that would dominate the next 25 years of truss history.