Shaking Buildings to Unlock Greater Heights

A simulation tool developed at the University of California, San Diego (UCSD), is transforming researchers’ understanding of how tall cold-formed steel (CFS) buildings withstand real earthquakes. The tool could also provide a future blueprint for safer, more resilient buildings that communities can rely on during earthquake recovery. 

With the help of National Science Foundation (NSF) funding in 2022, UCSD upgraded its shake table to move in six degrees of freedom across three axes, replicating real seismic forces.

In May 2023, this apparatus was used as part of a real-world test on the Tallwood building—a 10-story mass-timber structure that was the tallest full-scale building ever to be constructed and tested on an earthquake simulator.

Tallwood underwent simulations of two of the most destructive earthquakes in recent history, equivalent to the 6.7 magnitude 1994 Northridge earthquake and the 7.7 magnitude Chi Chi earthquake that took place in Taiwan in 1999.

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This summer, the team went another step further by testing a 100-ft-tall, 10-story steel building on the shake table. According to UCSD, its shake table is the only outdoor facility of its kind in the world and the only simulator capable of testing a building of this height. The building also underwent simulations of the 1994 Northridge earthquake, plus the 6.9 magnitude Loma Prieta earthquake of 1989.

The test captured valuable data on how a tall CFS structure responded to multi-directional earthquake forces. These findings could inform whether current height restrictions—set by the American Society of Civil Engineers (ASCE) 7 Standard, which limits CFS buildings in seismic zones like California to six stories or 65 feet—can be safely increased.
 

Shake table 

The table uses a hydraulic system containing 9,500 liters (2,500 gallons) of hydraulic fluid, pressurized with nitrogen to drive V-shaped horizontal and vertically placed actuators. When pressure hits one end of an actuator, it pushes while the opposite end retracts. Researchers can isolate specific actuators to focus movement on a single axis or engage multiple actuators to recreate rolling, pitching, or twisting motions.  

“If you have a large or irregular foundation of a building, you could have rotation imposed at the base of the building during an earthquake. You could use the shake table to impose this rotation history,” explained Tara Hutchinson, earthquake engineering theoretician and experimentalist at UCSD. 
   
The table is the only one in the world capable of testing buildings that are more than 90 feet tall. Two years earlier, a different team examined earthquake effects on a 115-foot-tall mass-timber structure, which was the tallest building to ever be tested on an earthquake simulator.  

The shake table’s platen, or platform, is 40 feet by 25 feet, which set a practical limit for the footprint of the structure under test. Building a specimen larger than the platen would require extra engineering solutions like sliding bearings to handle movement beyond the platen’s edge.  

To simplify testing and attachment, the designers kept the building's footprint within the table’s dimensions. This choice enabled a direct attachment using stiff steel transfer plates post-tensioned to the table and avoided more complex methods like poured-in-place concrete. 

Rebuilding after an earthquake 

Scientists defined a “service level earthquake” (SLE) as a hazard level that an engineer should target for a building that they would like to immediately return to service following an earthquake. Engineers aimed to ensure that the building remained operational and suffered little damage, allowing immediate occupancy after the event without significant repairs.

Earlier design methods mainly focused on preventing loss of life (due to partial or full collapse) during major earthquakes, while performance-based design accounted for multiple levels of seismic activity. 

“An SLE event is a more frequent earthquake, with a 50 percent probability of exceedance in 30 years, which translates to a 43-year return period event. In other words, if this building has a service life of 50 years, an SLE event is going to occur,” Hutchinson explained. 

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This contrasts with a design-level earthquake, or risk-targeted maximum considered earthquake (MCER), which is both a much more severe event for which the primary design objective sought is to prevent loss of life by avoiding total structural collapse, even if the building sustained extensive damage and requires demolition afterward.   

“The level of intensity of a very rare earthquake is associated with a 2 percent probability in 50-year event, which roughly is associated with an occurrence every 2,500 years or so,” Hutchinson said. “It may happen in our lifetime, it may not. Given the uncertain timing, buildings need to be designed to assure they will not collapse considering this severe, but rare event.”  

To understand how their test building performed under a range of earthquake hazard levels, from SLE to MCER, researchers sequentially imposed 18 different earthquakes on the specimen. They also partnered with industry to include stairs, fire sprinklers, gas lines, roof-mounted equipment, windows, doors, finishes, and other elements to see how they reacted during each test and how they impacted the likelihood of immediate return to function.  

Impact on building codes 

This research used real-world data from large-scale building tests to drive the ongoing push in U.S. building codes toward functional recovery. Rather than relying solely on observational data from past events, these large and full-scale experiments provide a vital link between the expected seismic forces and a building’s actual response.  

"Full-scale building tests are crucial to support the communities’ desire to advance building code definitions in the realm of functional recovery,” Hutchinson stated. “They provide the essential, real-world data needed to understand how our infrastructure will behave, bridging the gap between seismic expectations and real-world performance.” 

Data analysis is underway and the team expects to soon publish its findings, with the hope of translating this knowledge into practical changes for future building codes. While some construction practices could shift immediately, incorporating new information into codes will require a rigorous, time-intensive process. 

Nicole Imeson is an engineer and writer in Calgary, Alberta.