Structural engineering researchers from a number of American universities gathered in San Diego for a week in late July to put a two-storey wooden structure through a series of powerful earthquake simulations.
Their goal was to gather the data required to design wood buildings as tall as 20 storeys that do not suffer significant damage during large earthquakes.
The research team is headed by Shiling Pei of the Colorado School of Mines.
The tests were funded by the U.S. National Science Foundation (NSF) and a variety of industry sponsors. Tests were done on a shake table at the University of California, San Diego.
Pei says the research is going beyond simply designing buildings that are safe during large earthquakes. He says the team is working to minimize the amount of time that buildings are out of service after quakes. The team, he said, is also focused on cutting the cost required to repair the buildings.
Based on the insights the team gleaned during the tests, the researchers will return to San Diego in 2020 to build, shake and ultimately burn an earthquake-resilient 10-storey timber building on the shake table.
The first round of tests a few weeks ago was conducted on a wooden structure 6.7 metres tall. Researchers were studying the behaviour of full-scale seismic safety systems made from advanced wood materials — including rocking walls — and innovative seismic safety designs for the structural elements in the building’s floors.
The wood used in the test structure was primarily cross-laminated timber (CLT).
Pei says that “with the arrival of cross-laminated timber, we can start thinking about timber skyscrapers.
“CLT and mass timber are part of a massive trend in architecture and construction, but the seismic performance of tall buildings made from these kinds of wood is uncharted water.”
Some tall wood buildings have been constructed in recent years, but they have generally been built in areas thought to be seismically inactive, or they have been constructed with seismic safety systems made from non-wood materials such as concrete and steel.
An intriguing part of the research is what engineers are referring to as rocking-wall systems. These are vertical, mass timber walls connected to the foundation by post-tensioned rods that run up through the floor and special U-shaped steel energy dissipaters. The rods allow the wall to rock during an earthquake then snap back to its original upright position. It is hoped the system will minimize deformation and the resulting structural damage.
Current seismic safety building codes aim to ensure human safety in large earthquakes, allowing buildings to stand long enough to permit occupants to leave unharmed. The codes, however, don’t necessarily ensure that occupants will have a building to return to.
The key objective of the research is to devise ways of designing buildings so they can be back in service soon after a large earthquake and with minimal repair costs. In other words, the researchers are looking for ways to design earthquake resiliency.
“Building owners want to know, after a large earthquake, ‘how many months am I out?’ We want to be able to say ‘you’ll be out for a week and the building will likely just need repairs to a few systems that are designed to be damaged.’ ”
Researchers paid close attention during the July tests to how different seismic safety systems interact with each other during realistic earthquake simulation.
“We have tested the rocking walls by themselves in the lab,” Pei says. “But as structural engineers, we know that the system is not equal to the sum of its parts. There are interactions between the parts. That’s why projects funded by the NSF are so critical.
“We are finally going to be able to get data on how the different components function as a system during strong earthquakes.”
Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@journalofcommerce.com.
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