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A Code for Our Time

FullTextImage/img/@altGiustino Iuliano ’16 and Col. Grigg Mullen ’76 test the load capacity of a beam. -- VMI Photo by H. Lockwood McLaughlin.

Summer Research Project Tests Load-Bearing Capacities for Timber-Framing Construction

LEXINGTON, Va., July 15, 2013 – Giustino Iuliano ’16 may be new to civil engineering, but he hasn’t wasted any time getting hands-on experience in his major field.

This summer, he’s working alongside Col. Grigg Mullen’76, professor of civil engineering, to test the load-bearing capacity of floor joists used in traditional timber framing construction.

The project is part of a larger effort by Mullen, a timber framing expert, to contribute to the knowledge base of that ancient art so information about the load-bearing capability of beams can be included in modern building codes.

“Historical precedent works, but modern building code folks want proof,” said Mullen, who’s been involved with timber framing for over 15 years. “As an engineer, we need something to hang our hats on instead of, ‘Well, it’s always been OK.’”

To help expand the knowledge base for types of wood commonly found in Virginia, Iuliano is testing 12-foot timbers cut from four tree species: white pine, white oak, red oak, and poplar. For each type of wood, Iuliano is testing joists cut at three depths: two inches, three inches, and four inches.

Moisture is a critical component in determining the strength of wood, so Iuliano measures the moisture content of each timber by weighing a sample, drying it in an oven and weighing it again afterward.

“Historically timber frames are built with green wood, so the frame is weakest when it’s first assembled,” said Mullen.

Left to dry on their own, added Mullen, heavy timbers such as those Iuliano are testing could take up to a decade to dry completely. The oven simply speeds the process, he explained, so moisture content can be part of Iuliano’s calculations.

So far, Iuliano has found that the wood is losing a quarter or more of its weight in the oven.

While the small pieces of wood are drying, Iuliano tests the timbers themselves. Using a jack similar to one used to lift an automobile, Iuliano applies pressure to each piece of wood for 20 minutes to measure how much stress the wood can take before cracking.

“We add pressure as a wind load,” Iuliano explained. A load cell attached to the jack records the amount of pressure applied in each test.

So far, Iuliano has found that the strongest of the massive timbers – a piece of white oak with a four-inch joist cut – withstood 28,000 pounds of pressure. By contrast, a piece of white pine with a two-inch cut failed at only 6,000 pounds.

A typical residence, said Mullen, is usually designed to take about 2,000 pounds of pressure. “That’s when you’re having a frat party and everybody’s dancing,” he added.

Mullen and Iuliano plan to present the results of their work at a meeting of the Timber Framers Engineering Council, to be held Aug. 7 in Burlington, Vt. “The goal [of that organization] is to get timber framing covered in the design codes,” said Mullen.

He continued, “The standard 2 x 4 construction stuff is well covered by the codes. It’s the green heavy timber that drives the building code folks nuts.”

The longevity of timber frame buildings is not in question. On a trip to England, Mullen once visited inside a timber frame church built in A.D. 600 “If you keep a roof on it, it’ll stand forever,” he said.

–Mary Price