Researchers at the University of Alabama are testing whether tall, wood-framed buildings built with a hybrid technique that combines conventional construction materials and a newer material called cross-laminated timbers can better withstand earthquakes.
“We are trying to figure out this type of building. And how to change the building codes,” said Thang Dao, an assistant professor of civil, construction and environmental engineering.
The team members, whose work is funded through a 2015 National Science Foundation grant, simulated earthquakes of varying strengths as they tested a two-story hybrid structure constructed in UA’s Large Scale Structures Lab on Friday.
The structure, complete with interior stairwell, a second-story deck and furniture, was constructed with traditional light wood frame system and the emerging method of cross-laminated timber, or CLT, an engineered wood panel usually consisting of layers of wood glued at intersecting angles. The layer wood performs like larger whole timbers, Dao said.
The assumption is by combining the systems, which each have beneficial features, it will create a more resilient buildings in seismic zones in the United States.
There are structural benefits to the hybrid build. CLT is very stable and, Dao said. The light frame construction dissipates energy well. One is too rigid and one is too soft. But if you combine them, you can harness both their strengths. The dynamic between the two wood style is like a spring and dampener, he said.
“That is why we are trying to combine them,” Dao said.
Dao is working on the project with Sriram Aaleti, an assistant professor of civil, construction and environmental engineering, and John van de Lindt, a professor of civil and environmental engineering at Colorado State University.
The team at UA has been working on the project for 3.5 years. The hybrid structure is the first of its size to be tested, Dao. Ahead of the full structure test, the team tested individual components and computer modeling as they worked on designing the test structure.
The test of the mock-up of the two-story structure allows the researchers to study how the components such as walls and floors in a hybrid construction perform together during an earthquake.
“Now we see if what we assume is correct,” he said.
Tu Ho, a Ph.D. student in civil engineering working on the project, said the sensors on the structure Friday measured lateral and vertical movement as well as acceleration.
The hope is the research will lead to the construction of wood-framed buildings that could be eight to 12 stories, Dao said. The buildings top out at about six stories currently.
In addition to the structural considerations that seek to combine the benefits of both styles, the researchers' work is influenced by the affordability of the materials.
“Light frame is cheap. That is why it is so popular now,” Dao said.
The CLT is more expensive, he said. By using a hybrid design, Dao said the hope is to make using CLT more affordable and help accelerate its adoption and eventually bring the price down.
“If you use all CLT, it is too expensive to build,” he said.