NHERI to investigate resilience of tall timber buildings by earthquake simulator tests

Homebuilding

Image: Rendering of the construction site for the Natural Hazards Engineering Research Infrastructure (NHERI) TallWood project / LEVER Architecture

The Natural Hazards Engineering Research Infrastructure (NHERI) TallWood project, in which Colorado State University (CSU) 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 U.S. 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 longtime colleague and former student, Shiling Pei.

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.

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 nonstructural 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 nonstructural 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.