Day: March 31, 2009

Tech Today

by Marcia Goodrich, senior writer

Deep in the stacks of the J. R. Van Pelt and Opie Library, Joe Miller stumbled upon a 112-year-old book that gave him a start.

Miller is a civil engineer specializing in heavy-timber roof design. He settled at Michigan Tech to get his PhD and to learn more about keyed beams than anyone in the history of carpentry. Keyed beams, lovely and useful though they may be, are in one sense an also-ran in the world of wood.

Miller explains in the context of the Upper Peninsula, where the old-growth, white-pine forests were ferociously clearcut in the 19th century. “By 1900, all the large trees were forested,” he said. The massive timbers required for constructing large buildings and reinforcing mine tunnels were no more. Builders needed a cheap, local alternative, so they began making big beams out of two smaller ones.

They cut mated notches in the lesser beams, fastened them together, and pounded close-fitting wedges, or keys, into the notches. The technique keeps beams stiff and bound tightly together, which prevents them from slipping (and breaking prematurely) when heavily weighted in the middle.

Keyed beams have been around since the 18th century. More recently, builders have adopted other technologies, but they aren’t always popular. “A lot of my clients had problems with steel beams or glue-laminated timbers,” Miller said. “Aesthetically, they wanted to use a more-natural approach that could be achieved locally, with local materials.”

Now, with keyed beams gaining a new following, Miller is developing the first theoretical model to represent their capacity under load. In other words, how much weight can they take before they break? And what factors determine if a keyed beam will be stiff enough?

Which brings us back to the library and the 112-year-old book. Miller was perusing the library’s offerings on the subject when he stumbled across an 1897 reference volume, buried in the basement, authored by Edward Kidwell of Hancock.

Kidwell, as it turns out, was on the faculty at the Michigan School of Mines. And he was one of the earliest researchers to conduct valid scientific tests on keyed beams and document the results. “It wasn’t until I’d chosen a school and a dissertation topic that I found his book,” Miller said, still struck by the coincidence. On top of this, Miller found Kidwell’s century-old reports to be both reliable and engaging.

“I appreciated his candor,” he said. In the book, Kidwell was critical of earlier keyed beam experts whose assertions did not stand up to scrutiny. “I also tested his methods, and everything he said appears spot on,” Miller said. “And Kidwell provided enough detail so that I could plug his numbers into my model.”

In addition to working with Kidwell’s findings, Miller has been testing his model against experimental evidence gathered in his own lab, where he has been building and testing keyed beams fabricated from solid oak, yellow poplar and wood laminate. “I’ve found that the inclination and shape of the keys can have an incredible effect” on the strength of the beam, he said.

“To be reinvestigating a concept that’s been around 300 years is kind of cool,” he said. It’s also cool to be building on foundational work conducted right here over 100 years ago.