Oftentimes, we'll take the stairs to get in those few extra steps. As we climb toward better health, do we consider how much strength lies in the wood beneath our feet? While we may not think twice about the actual steps we take, there are others who do. The Stairbuilders and Manufacturers Association has partnered with scientists in the MSU Forest and Wildlife Research Center to assess the wood commonly used in constructing stairs.
Dr. Fred França, assistant research professor in the Department of Sustainable Bioproducts, is co-principal investigator on a three-year study that evaluates design values of domestic species in stair and guard construction. The team includes Drs. Jason Street, Rubin Shmulsky, Dan Seale, and Thomas Lim. França's group is focused on wood used in stair construction while Lim's team evaluates wood used in stair guard construction. The study is in its second year.
França's group is evaluating 1500 boards from five U.S. tree species. Four species are hardwoods including hard maple, yellow poplar, red, and white oak. The team is also evaluating the softwood, southern yellow pine. França said this is one of the first studies of its kind in almost 100 years.
"Much of the research stair builders and manufacturers currently rely on was conducted in the early twentieth century," França explained. "Our goal is to examine current design values used for domestic species and grades used in stair and guard systems and provide necessary technical information to update them as needed."
The team is conducting destructive testing on 300 boards from each species and assessing four mechanical properties including static bending, compression parallel to the grain, compression perpendicular to the grain, and Janka hardness—the resistance of wood to denting and wear. They are also assessing the physical property of specific gravity and two growth characteristics: the number of rings per inch and the percent of latewood, the part of the wood in a growth ring produced later in the season.
Lim, an assistant professor in the Department of Sustainable Bioproducts, is developing a computer model that can simulate the structural behavior of staircase guard systems. The modeling focus will be on predictions of the structural performance of the joints keeping the guards together. The model's accuracy will be confirmed using destructive test data, which will be collected as a part of the project.
"The successfully developed tool will be an alternative means over expensive destructive tests in evaluating the structural performance of staircase guards built with different wood species and dimensions," Lim said.
While the research is still ongoing, França hopes the ultimate findings will help stair builders and manufacturers select for wood species that result in sturdier steps.
"The development of design values for appearance grade domestic lumber will provide innovative ideas and solutions for the use of U.S. lumber in stair and guard construction," França said. "The opportunity to increase world demand of high-grade U.S. lumber for structural and architectural millwork is timely. U.S. building regulations are striving to enforce stricter structural requirements with more than an approving jump on the stairs or bump of the rail as has been the case for years in residential construction."
Graduate students on the project include sustainable bioproducts doctoral student, Nathan Irby, and master's students: Laurice Mara Spinelli Correa, Cristian Grecca Turkot, and Marly Carmona Uzcategui.