110 Years of FPL: Strength Testing

In celebration of 110 years of research at the Forest Products Laboratory (FPL), we are revisiting blog posts that detail some of our most interesting historic people, places, and projects. Enjoy!

A 1950’s test of a large wood cylindrical structure in the 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.

Wood Tornado Shelter Provides Safe, Affordable Storm Protection

USDA Forest Service researchers have developed a tornado shelter made of wood that provides powerful protection at an affordable cost.

With safety and security in mind, Forest Products Laboratory (FPL) engineers designed the residential tornado shelter to resist the high wind pressure and debris impacts generated by high-wind events.

Most importantly, the wood shelters can be built into an existing home using readily available materials and tools.

A F3 tornado sets down in a field. Image credit: Clint Spencer via iStock
Continue reading

Tales from the Test Floor: Air Cannon Makes a Perfect Shot

Researchers at the Forest Products Laboratory (FPL) are back to work using the debris launcher in the Engineering Mechanics and Remote Sensing Laboratory.

The debris launcher is an air cannon that fires two-by-fours at 100 mph to replicate what could happen in a house or any wood structure during a tornado. The equipment has been used frequently over the past several years, most recently to test the viability of tornado safe rooms constructed of wood.

This time, researchers are using the cannon for a new purpose: shooting the lumber ‘missiles’ at sections of cross laminated timber to test the engineered material’s performance withstanding projectiles in high-wind events, and there was a surprise ending to the test.

The missile was fired at the test wall, and it bounced off the wall…right back into the cannon! Take that, cannon!Missle  after testSeems like a one-in-a-million shot. But wood, er, would you believe it happened twice?! Goes to show that even after more than a century of research at FPL, good ol’ wood still has a few tricks up its bark, er, sleeve.

 

Tales from the Test Floor: Glulam Arches

IMG_8603

Researchers here at the Forest Products Laboratory (FPL) wrapped up testing a set of glued laminated (glulam) arches with a bang by breaking the last arch in a series of three. The arches measure 30-feet tall by 30-feet wide. Only ten arches have been tested worldwide.

This experimental work is evaluating the seismic design parameters of glulam arches by simulating the forces of an earthquake and measuring how the arches perform under such stress. The collected data will be analyzed and results published in the near future to serve as a reference for architects and engineers looking to design buildings using glulam arches.

The test took place on the strong floor in FPL’s Engineering Mechanics and Remote Sensing Laboratory (EMRSL). Here, researchers conduct physical and mechanical tests on a wide range of materials, building systems, and structures – from houses to bridges. Results inform the development of building codes and structural design standards.

 

Re-evaluating Evaluation : New Materials, New Methods

In today’s world of energy-efficient building requirements, structural insulated panels (SIPs) remain an attractive option. Modern SIPs combine the strength of wood with the energy-saving attributes of cutting-edge foam plastic insulation, to create a cost-effective solution for construction professionals. These sandwiched panels stand ready to meet the building codes of tomorrow, but many fear that the lack of adequate, systematic testing of these new materials may hinder their popularity and stifle their widespread implementation.

The Forest Products Laboratory (FPL), APA – The Engineered Wood Association, and the Structural Insulated Panel Association are on a mission to change this. Because of their unique construction, researchers believe SIP walls must be tested differently than more common light-frame walls. Unlike traditional walls, SIP walls are required to bear weight on their cap and sill plates, so that vertical loads from the story above are effectively transferred down to the foundation.

Creep test setup for a structural insulated panel.

A structural insulated panel undergoing performance testing at FPL.

This “restrained” method of evaluation yields the most accurate data for SIP performance.

Until recently however, SIP walls have been evaluated in the same way as their conventional light-frame counterparts, using an “unrestrained” configuration. Researchers fear that these tests may not realistically reflect the lateral load-bearing ability of the SIPs.

SIPtest

A diagram illustrating how the 24 full-size SIPs will be tested.

Between May 2015 and August 2016, 24 full-size SIP walls will undergo a carefully monitored regime of restrained, lateral load performance tests, which represent the most common configurations used by industry professionals. Researchers will consider a wide range of variables — from the obvious, such as wall thickness and type — to the minute, such as nail size and nail spacing. The final report will be prepared by December 2016.

Results of this project will not only increase the accuracy SIP performance data, it may help guide further evaluations of similar building materials in the future. Most importantly, it will provide construction and design professionals with the data they need to make informed choices when considering these new building materials, so that they can keep tomorrow’s buildings efficient and safe.

For more information, please see this Research in Progress.