A Strong History: Strength Testing at FPL


A 1950’s test of a large wood cylindrical structure in the aptly named “1,000,000-pound capacity” testing machine. This machine was also used to evaluate poles, piles and large wood beams.

Forest Product Laboratory (FPL) researchers established selection and testing procedures for determining strength properties of wood, which were adopted as standards by ASTM International (formerly the American Society for Testing and Materials, ASTM). These standards have, in recent years, had an important bearing on the development of comprehensive international standards sponsored by the Committee on Mechanical Wood Technology of the Food and Agricultural Organization of the United Nations.

Strength testing research conducted by FPL employees included the following categories:

Toughness Testing
FPL developed a machine to test the ability of wood to absorb shock or impact loads. The toughness test procedure and machine have become standard both nationally and internationally.

Strength Factors
The staff determined the effect that knots, preservative treatment, decay, moisture content, and other factors have on wood strength. This work has resulted in increased safety, marked improvement in efficiency, and increased satisfaction in wood use.

Low Temperatures
FPL carried out research at temperatures as low as -300°F, which showed that—far from becoming weak and brittle at low temperatures—wood actually gets stronger. This data established wood’s advantages for construction in frigid areas and have helped established new uses for wood, such as structural insulation in commercial barges that provide low-cost, world-wide transportation for liquid methane.

Decayed Wood
FPL evaluated the properties of Douglas-fir lumber cut from timber infected with a fungus called white pocket, to show how it could be used effectively. As a result, Douglas-fir sheathing and dimension grades are permitted to contain certain amounts of white pocket. Over-mature timber previously left in the woods can now be harvested and used more effectively.

Long-Term Loading Effects
Most strength testing of wood reveals the reaction of wood to the application of loads over a very short time. Most wood used in structures however is expected to carry load for long periods of times. The FPL has therefore carried out long-term loading experiments to develop data to support engineers and design professionals.

This blog post has been adapted from Forest Products Laboratory 1910-2010: Celebrating a Century of Accomplishments.