Buildings made of mass timber – layers of wood bonded together – are gaining popularity as greener and faster alternatives to concrete and steel structures. With new building codes recently updated to permit more high-rise mass-timber buildings to be constructed in the United States, many have questioned how such buildings would fare in earthquakes. Source: Timberbiz
The Natural Hazards Engineering Research Infrastructure (NHERI) TallWood project, in which Colorado State University engineering researchers are playing a critical role, aims to investigate the resilience of tall timber buildings by simulating a series of large earthquakes on a full-scale, 10-story mass timber building this spring – the world’s tallest full-scale building ever tested on an earthquake simulator, or shake table. The research project is funded by the US National Science Foundation.
John van de Lindt, professor in the Department of Civil Engineering and an expert in seismic analysis and resilience, is working on the project with a long-time colleague and former student, Shiling Pei. Pei is principal investigator of the Tallwood project and is a civil engineering faculty member at Colorado School of Mines.
Throughout the project, van de Lindt and his CSU students will help assess the damage inflicted on the building from a resiliency perspective and estimate how long it would take the building to return to its normal function following an earthquake. The technical term is “functional recovery” and is likely the future of structural design codes in the United States, van de Lindt said.
“Working with Ling (Shiling Pei) and the other members of the Tallwood team, including all the industry partners, to get this test ready has been an amazing experience,” Mr van de Lindt said. “Although I’ve done a number of full-scale whole building tests around the world, each one has unique challenges and opportunities: the people, the place, the schedule, but most of all the discovery.”
Mass timber is part of a growing trend in architecture and construction, but the seismic performance of tall buildings made with these new systems is not as well understood as other existing building systems, Pei said.
The team designed a 10-story tall, mass timber rocking wall lateral system suitable for regions with high earthquake hazard. This new system is aimed at resilient performance, which means the building will have minimal damage from design level earthquakes and be quickly repairable after rare earthquakes.
The rocking wall system consists of a solid wood wall panel anchored to the ground using steel cables or rods with large tension forces in them, according to Pei. “When exposed to lateral forces, the wood wall panels will rock back and forth – which reduces earthquake impacts – and then the steel rods will pull the building back to plumb once the earthquake passes,” he said.
Due to this seismic movement induced by the rocking system, resilience-critical non-structural components within and covering the building, such as the exterior facade, interior walls and stairways, are in for a big ride.
The project team focused on safety-critical non-structural components that span floor-to-floor and thus are subjected to the relative movement between stories. The building features four exterior façade assemblies, a number of interior walls, and a 10-story stair tower. The exterior envelope must protect the building from temperature extremes and weather events, while stairs must remain functional to allow occupants to safely exit and first responders to continually access all floors of the building.
The tests are scheduled to start in May on the world’s only outdoor shake table. Located at the Englekirk Structural Engineering Center at the University of California San Diego, the earthquake simulator is part of NSF’s Natural Hazards Engineering Research Infrastructure and, through NSF funding, was recently upgraded to six degrees of freedom to reproduce the full 3D ground motions that can occur during an earthquake. It is also now capable of testing payloads of up to 2,000 tons, or more than 4 million pounds.
Tests will simulate earthquake motions recorded during prior earthquakes covering a range of earthquake magnitudes on the Richter scale, from magnitude 4 to magnitude 8. This will be done by accelerating the table to at least 1g, which could accelerate the top of the building to as much as 3gs. For reference, fighter pilots experience up to 9gs of acceleration in flight.
In 2017, Pei’s team, including van de Lindt, carried out a test on a two-story mass timber building by simulating shaking from the Northridge Earthquake, a magnitude 6.7 earthquake that struck Los Angeles in 1994. The building was subjected to 13 earthquake tests and remained structurally damage-free. In addition to demonstrating that mass timber building systems can be seismically resilient, those tests helped the research team develop the design and analysis methods that have been used for the 10-story building.
