Are century-old timber beams as serviceable as new ones?

The reuse of materials is one of the most effective climate change mitigation strategies available to the building sector. However, used materials have to meet the same requirements as new ones when it comes to properties such as bending strength and elasticity.

The standards agency Standard Norge has prepared a draft standard for the visual strength sorting of reusable beams, which has now been sent out for consultation. This is why SINTEF has acquired a batch of century-old beams for testing in accordance with the NS-EN 408 standard, which is the same as that used to test new materials.

"We're measuring applied force and deformations, which will enable us to say a lot about the strength of the beams," says Senior Adviser Sigurd Eide. "Many of them exhibit properties that are at least as good as new materials," he says.

Is reuse possible without testing?

Reusable beams are gray in color and in many ways marked by the passage of time. It isn't always easy to judge the quality of the timber at first glance. Nevertheless, there are several external characteristics that can tell us a great deal about the strength of the timber.

"Before we test the beams, we record any cracks or notches," says Eide. "We measure the closeness of the annual rings and examine how the timber has been cut in relation to the orientation of the grain in the wood. Ideally, they should be cut parallel to the grain. The closer the alignment, the better. We also measure moisture content," he says.

"We thus have quite a good idea of which beams are strong enough, even before we test them," says Eide.

To date, the tests have confirmed the researchers' pre-test assessments of which beams will pass the strength test. The test results themselves will provide useful input to the consultation process for the new NS 3691-3 standard for the visual strength sorting of reusable beams.

Provided by Norwegian University of Science and Technology