Tallwood Design Institute

Developing Methods for Non-Destructive Testing for Mass Timber

The materials that go into structures must be reliable, and there are multiple levels of quality assurance, permitting, and inspection that aim to ensure that they are. For mass timber, manufacturers do their part on this front by completing a variety of quality assurance tests on the materials as they come off the manufacturing line, before they ever reach a building site. These tests, as laid out by current standards, include glueline delamination testing and shear testing and they allow manufacturers to confirm the quality of the elements they send out into the world.

Once a mass timber element reaches the construction site, it could also be exposed to moisture or other detrimental conditions before the envelope is completed. It’s possible that the materials will undergo delamination or decay due to this exposure or other factors in its service life. In these cases, the types of tests done to confirm quality of manufacturing could catch these issues as they occur, but sampling is significantly more costly once the structure is in place because these tests require testing a sample of the element itself to failure.

As more mass timber products and buildings enter the market, there is a growing need to develop methodologies that are capable of investigating the quality and health of structures without necessarily requiring destructive sampling of the members. In order to meet this challenge, TDI is supporting researchers investigating several non-destructive testing approaches in order to be prepared when the need arises.

Non-Destructive Testing

As the name implies, non-destructive testing includes a variety of quality assurance techniques that don’t damage the material in question. Tools for non-destructive testing make use of a variety of properties that can be correlated to the key features of interest, such as strength, stiffness, or bondline quality in a mass timber material. Part of the challenge in using these techniques on new materials lies in making sense of the resulting data. Before adding the complication of defects such as delamination and decay, the researchers need to understand what the baseline readings in engineered wood materials look like first.

Ultrasound Testing

In the Advanced Manufacturing Lab, Dr. Vahid Nasir, Ashley McCann, and Autumn Battisti are investigating the use of ultrasound to identify glue-line issues in CLT. They are working alongside Dr. Lech Muszynski and Samson Idoghor, who are creating CLT samples with known thickness variations for a related project on delamination effects, to test ultrasound sensors’ ability to identify areas of potential delamination inside the material.

Although not yet proven out, ultrasound would be a convenient approach for both quality assurance on the manufacturing line and on-site evaluation because it is completely non-destructive and comparatively portable. “Long term, we really think [detecting] defects such as delamination in in-line manufacturing and potentially in-situ is possible. This could be a valuable tool to catch any issues at a lower cost to manufacturers,” says Ashley.

Before joining Dr. Nasir’s lab, Ashley worked on another project investigating the variation of delamination within CLT panels, using the standard suite of destructive tests to do so. This project builds on their experience with identifying defects in the lamination process. Autumn, on the other hand, brings experience in the ultrasonic scanning of mass timber products, including CLT in this project and veneer-based products in another.

For the testing to work, the researchers needed to develop a standard methodology that can collect interpretable wave patterns. The shape and strength of the ultrasound waves are affected by changes in the medium they are traveling through. As Autumn explains, “for waves, what really matters is changes in the speed it can travel in the medium. The speed [the waves] can travel depends on how stiff it is and the density, so the closer that is to wood the less of an impact it has”. Air can significantly change the shape of the waves because of the large difference in density, but wood and adhesive have similar enough densities that traveling through mass timber doesn’t impact the wave shape as dramatically.

The team has been able to show that they can detect void gaps in CLT, and they are currently working on predicting the results of destructive testing using ultrasound in small-scale samples. If they can consistently detect these known features, the next steps will be to verify that the method also works on larger scale samples.

Vahid Nasir

Assistant Professor
Wood Science & Engineering
Oregon State University

Ashley McCann

Ph.D. Student
Oregon State University

Autumn Battisti

MS Student
Oregon State University

Resistance Drills

In the Biodeterioration Lab, Dr. Gerald Presley, Dr. Mariapaola Riggio, and Opeyemi Odule are taking a different approach by using resistance drills to develop methods to detect both delamination and decay in-situ in mass timber elements made of CLT and MPP. These drills are minimally invasive and are currently in use for monitoring decay in standing trees and utility poles. They also can enable the detection of problems within mass timber composites not visible to inspectors on surfaces.

Resistance drills are highly sensitive to the density of the medium so when used in whole log applications the data are interpreted in light of a regular pattern of earlywood and latewood in the tree’s rings. In mass timber, this pattern does not exist due to varied orientation of growth rings in different lamellae, or veneer based construction. Part of the work of this project is determining how to read resistograph data in different materials, since the readings are markedly impacted by both the gluelines and the orientation of the grain within the layers. This will help researchers better understand what resistance drill signals indicate intact mass timber panels.

To get a better understanding of how to separate natural defects from indications of water damage and decay, Opeyemi has spent the better part of a year inducing different levels of delamination and decay in samples of CLT and MPP, drilling the samples with two styles of resistograph, and then dissecting the pieces to identify features. This time series approach will allow her and the other researchers to correlate features in the data to features in the mass timber at different points in the decay process, developing a better understanding of the limits of the drill’s ability to identify changes in the structural health of wood materials.

Non-destructive testing is a key tool for establishing the quality of materials efficiently. Having techniques available for mass timber will benefit many aspects of the industry, from the manufacturing lines to the assessment of structures as they age, by enabling proactive responses to challenges inherent to building with wood.

Gerald Presley

Associate Professor
Wood Science & Engineering
Oregon State University

Opeyemi Odule

MS Student
Oregon State University

Non-Destructive Testing

Ultrasound Testing

Resistance Drills

Location