The Development of the Truss Plate, Part VI: An Industry Established

Issue #15282 - January 2023 | Page #10

By Joe Kannapell

On July 5, 1960, in a marathon session, a dozen entrepreneurs set standards for a brand new industry, and, in the process, met a government deadline. These early truss plate adopters came well-prepared and didn’t hesitate to make far-reaching decisions. Fortunately, they left a detailed record of their remarkable work, and their efforts continue to shape today’s plated truss industry.

They brought to Miami organization skills drawn mostly from their prior business experience and got right to work creating a new entity modeled on the highly regarded, thirty-year-old Steel Joist Institute. They reached quick agreement on a similar name for a new association, the Truss Plate Institute (TPI), and set down four main objectives. [For all images, See PDF or View in Full Issue.]

Quality control was the first, and remains so to this day, and the second was to “act as spokesman for the industry.” Because no industry existed at the time, this left open the means to achieve wide recognition.

Cal Jureit of Gang-Nail, who chaired the meeting, was elected the first TPI President, and his brother, Bill, was approved as legal counsel to prepare Articles of Incorporation. Discussion was held on the draft design criteria and a committee led by Bill McAlpine of Sanford Truss, Inc., was charged with completing the document. The most important outcome of the meeting was that FHA gave the new organization additional time to submit their design code for review.

By August 24, 1960, the first “Design Specification for Light Metal Plate Connected Timber Trusses, TPI-60,” was agreed upon, but it was not formally ratified until May of 1961. This 14-page document set industry standards for testing, design, and truss drawings that would long endure.

The first section called out the information required on truss drawings, the key factor in establishing code compliance and providing building officials with uniform truss submittals.

The following sections contained the design provisions, which were of crucial importance in securing the approval of FHA. These were adaptations of those found in the National Lumber Design Specification NDS-60. The only illustration, shown in part, provided generally conservative simplifications that proved to be expedient in this pre-computer, slide rule era.

In this initial edition of our TPI standard, there is scant guidance for the design of plated joints, except for a detailed procedure for calculating the stresses induced by eccentricity at heel joints.

Of current interest are these factors relevant to 1960’s design:

Lumber was 1-5/8” x 3-5/8”, 5-1/2”, 7-1/2”, 9-1/2”, and 11-1/2”.
Douglas Fir and West Coast Hemlock were the predominant species used in trusses outside of the South.
Spruce-Pine-Fir, Hem-Fir, and MSR were not yet available.
No. 3, Standard, and Stud grades were not listed in NDS and therefore were not assigned structural values. Consequently, TPI-60 states, “Web members with comparatively low stress, may be non-stress rated 2x3 or 2x4 culled to eliminate pieces with excessively large or loose knots.”

The remainder of TPI-60 concerned the testing of truss plates and full-scale trusses, which were essential in establishing the strength and durability of the new connectors. These protocols were largely based on Cal Jureit’s testing lab work in the early 1950s and his later work with Dade County. All three of the national codes soon adopted TPI’s truss plate tests but only the Building Officials and Code Administrators (BOCA) adopted TPI’s full-scale truss tests.

The timely, professional work of a few early innovators had a far-reaching impact on the building community. Code authorities would now have the proper basis upon which to approve plated wood trusses. Truss companies would be able to tout the advantages of a code-approved, quality controlled, and engineered truss system. And, finally, the Truss Plate Institute would be dedicated to bolstering the acceptance of plated trusses. In short, a new industry was initiated and was given the means to hit the ground running.

Excerpted tables and text courtesy of the Truss Plate Institute