Salvaging an American Icon with Ground-Penetrating Radar

Two Route 66 signs on the road at California Mojave desert highway – By AR Pictures

Imagine being able to look straight into a wood beam and know its structural integrity.

It’s almost like a super power, except its really just amazing science—science that Forest Products Laboratory (FPL) researchers are practicing in order to be at the forefront of investigative timber safety and restoration.

During a recent study, “Ground-Penetrating Radar Investigation of Salvaged Timber Girders from Bridges Along Route 66 in California,” FPL’s Adam Senalik, James Wacker, and Xiping Wang along with colleagues from Jiangnan University School of IoT Engineering, were able to practice this amazing science on two bridges located on Route 66.

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Technology Helps Turn Salvaged Trees into Moneymakers

When insect scourges run rampant through forested ecosystems they can leave behind entire stands of dead and dying trees – especially if that scourge is the spruce budworm. In the Upper Midwest, where the spruce budworm infests forests on a cyclic 30-50 year pattern, forest managers oftentimes use salvaged logs from the dead and dying trees to produce low-value wood products, such as wood pulp, or merely count the dead trees as a loss and leave them standing.

Spruce budworm mortality,
National Forest, Summer
2014 (Steven Katovich, USDA
Forest Service,

But Forest Products Laboratory (FPL) researchers developed ways to evaluate the quality of salvaged wood and sort out the higher-quality wood for production of cross-laminated timber (CLT) – a high-value wood product that can increase forest revenues. “We’re at the point of demonstrating commercially available technologies,” said FPL engineer Robert Ross, “and the idea that we can take high-grade material out [of dead tree stands].” Continue reading

The End of an Era: Eagle Tower's Last Day

Eagle Tower, a wooden observation tower standing 75-feet tall and rising 250 feet above Lake Michigan, was built in 1932 in Wisconsin’s Peninsula State Park. A Door County icon, this well-loved landmark served visitors for generations, but an in-depth inspection conducted in the spring of 2015 indicated the structure was in poor condition and no longer safe for the public.eagletower

The inspection included core sampling to determine the general internal condition of the structural components and overall load-bearing capacity of the structure. On May 20, 2015, the tower was closed for public use. Eagle Tower was taken down on Sept. 19, 2016.

Researchers at the Forest Products Laboratory (FPL) were asked to help in the evaluation of Eagle Tower as the Lab has extensive experience in historic structure evaluation and nondestructive wood evaluation techniques. FPL researchers will be testing the dismantled wood members and determining if they can be reused in any way to pay homage to the historic tower.

Community members are currently raising funds for the tower’s reconstruction. The new tower will comply with the Americans with Disabilities Act, current construction codes, and take into consideration new construction technologies.

The Wisconsin Department of Natural Resources put together a slideshow of the deconstruction of Eagle Tower so the public could view the event.

‘Landmark Book’ Covers Nondestructive Testing of Wood

ross cover CROPPEDThe USDA Forest Service Forest Products Laboratory (FPL) has assembled the most comprehensive publication ever regarding the nondestructive testing and evaluation (NDE) of wood materials.

Geared toward industry professionals, Nondestructive Evaluation of Wood, offers guidance, analysis, and practical application of NDE techniques, including the use of lasers, x-rays, and ultrasound, to assess and report on the condition and integrity of wood.  These techniques, which do not damage the objects being evaluated, can be used on structures, bridges, standing trees, and even historic artifacts.

“Nondestructive testing of wood is an exciting area of research and has the potential to greatly enhance the wise use of wood,” said Bob Ross, the book’s editor, an author or co-author of several chapters, and a supervisory research general engineer at FPL. “Wood, in any form—trees through timber bridges—is highly variable because of how it grows, where it comes from, and what it is exposed to. Nondestructive evaluation technologies are the scientific foundation for all assessment and grading of wood-based materials,” Ross added

The book’s 13 chapters contain information from many of the industry’s foremost experts in the world, on topics such as static bending, transverse vibration, resistance drilling, piezoelectricity, acoustic assessments, and laser methodology. The book also provides information concerning more traditional evaluation techniques, such as machine grading, and advice for practical application in urban environments.

“To make the best, highest use of our forest resources,” Ross explained, “we need to have technologies that help us assess what the quality of a particular tree, log, or piece of lumber is. We can then utilize it appropriately. One of the fastest growing sectors of the wood products industry—engineered wood products—relies heavily on the use of nondestructive evaluation technologies.” NDE techniques described in the book have been employed around the world in many projects:

  • Use of sound waves to evaluate the quality of timber in National Forests
  • Use of ultrasound technology to locate decay in urban trees
  • Evaluation of structural performance potential of logs, veneer, lumber, and timbers before installation
  • Inspection of historic covered bridges
  • Inspection of historic artifacts,including the USS Constitution and a 2,500-year-old mummy coffin from Egypt

“This landmark book continues the proud legacy we have established at the Forest Products Laboratory as a cutting-edge scientific institution,” said FPL Director Michael T. Rains. “It represents years of research across the full spectrum of scientific endeavor, from technical journals and research reports, to the proceedings from various symposia. The book will serve as a guide to the public and a touchstone for future generations of scientists and land managers, as we continue to find better ways to utilize one of our planet’s most cherished and renewable resources—wood.”

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Wood vs. Water: Who Will Win - the Cabin or the Creek?

One thing we know for sure at the Forest Products Laboratory (FPL) is that wood and water don’t mix, and keeping wood dry is essential to long service life. So really, 80 years seems like a good, long life for a log cabin built with untreated logs, situated just 10 meters from a river in an area with high snowfall, and subjected to the subsequent spring melting that follows each winter. For this cabin, maintained by Michigan Technological University’s School of Forest Resources and Environmental Science, staying dry has been nearly impossible.

Otter River cabin, 2013.

Otter River cabin, 2013.

Situated on the north branch of the Otter River in the Portage Township of Upper Michigan, the cabin was built in 1934-1935 by the Civilian Conservation Corps and housed workers who used the site as a trout hatchery. In 1955, it was transferred to Michigan Tech with promise that public rights of hunting, fishing, and trapping would be maintained. Over the years, continuous maintenance was needed due to periodic flooding and the resulting log deterioration.

Since 1998, Michigan Tech and FPL have cooperated to conduct periodic inspections of the cabin. The latest inspection, completed in 2013, utilized various techniques to analyze the condition of the log cabin.

Some decay was obvious with visual inspection alone.

Some decay was obvious with visual inspection alone.

Visual inspection is the simplest method for locating deterioration. Here, researchers look specifically for evidence of water intrusion and damage, especially near the foundation, and evidence of structural failure of the timbers. Many of the logs showed signs of severe deterioration, with the ends of several having been entirely destroyed.

Sound transmission measures the time it takes for stress waves to travel between sensors placed on opposite sides of a timber. Significantly longer transmission times, relative to the base times known for several species, indicate the presence of deteriorated wood. Nearly half of the tested logs produced results in the ‘deteriorated’ or ‘severely deteriorated’ range.

Micro-drilling resistance test of wall timber.

Micro-drilling resistance test of wall timber.

Micro-drilling resistance is a commercially developed technique based on the underlying premise that degraded wood is relatively soft and will have low resistance to drill penetration. Researchers conducted micro-drilling resistance tests in areas of the timbers they believed contained decayed wood based on results from the visual assessments and stress-wave testing. Test results showed that many logs were deteriorated, with most having an outer shell of solid material but a severely degraded core.

In the end, these test results showed that water had finally won the war over wood. Researchers recommended the cabin be dismantled, salvaging any possible historic materials (hardware and any sound timber), and suggested a smaller structure be built on the site using the salvaged materials where appropriate.

For more information on the project, see this FPL Research Note.