A 10-story wooden tower swayed and rocked on the University of California San Diego shake table in summer 2023, enduring earthquake after simulated earthquake before settling back to perfect vertical—a performance that captivated engineers and revolutionized resilient construction.

After 88 simulated earthquakes, many exceeding building-code requirements, the tower remained structurally intact, marking a breakthrough for the Natural Hazards Engineering Research Infrastructure (NHERI) Tallwood project and challenging decades of assumptions about wood construction in seismic zones.

Today, thanks to this U.S. National Science Foundation-funded research, the story of tall wooden structures is entering an important new phase, as researchers work with industry supporters to get Tallwood’s mass-timber seismic design adopted into U.S. building code, known as ASCE-7.

Builders worldwide recognize the advantages of wood construction for tall buildings. Timber is resilient, renewable, and architecturally striking. As of 2024 in the U.S., more than 2,000 mid-rise and high-rise mass-timber buildings have been built, designed, or are under construction, according to media company Wood Central.

Professor Shiling Pei of the Colorado School of Mines, Tallwood lead investigator, envisions a new era in seismic design: “As a brand-new building type, the tall mass timber building can be a game changer in regions with high seismicity. We proved that, if designed right, you can essentially have an earthquake-proof building.”

Tall wood buildings in seismic zones

In earthquake-prone regions, however, there are practical limits for tall wood buildings. Current building codes limit wooden structures to six stories (or 85 ft) if they employ wood-based lateral systems – that’s the vital structural element that resists side-to-side earthquake shaking.

As a result, tall wood buildings in high seismic regions like the U.S. West Coast typically employ concrete or steel for these lateral systems, often referred to as “shear walls” or “braced frames.”

But effective wood-based lateral systems do exist, as Pei set out to demonstrate. He was convinced that tall wood buildings constructed with a mass-timber lateral system — a post-tensioned rocking-wall system specifically— are not only viable but preferrable in seismic regions.

From Mines, Pei organized a multi-faceted research consortium that included members from nine universities, funded by six individual NSF grants. With financial, consulting, and material support from dozens of industry partners, the Tallwood team designed a 10-story, mass-timber structure that would resist earthquake shaking and serve as a model design for tall wood buildings in seismic zones. The building was constructed directly on the platen, or surface, of the NHERI at UC San Diego shake table, the world’s largest outdoor shake table.

“This project is truly an international effort,” Pei said. “We referenced ideas in post-tensioned timber design from New Zealand, built our structures with wood from the U.S., Canada, and Europe, and relied on technical expertise from our collaborators and their students from Japan, Italy, Portugal, and England.” He added: “Large scale testing projects are extremely difficult but rewarding at the same time, made possible by the NSF shared-use facility framework and the openness of the U.S. wood industry and our engineering research community.”

The mass-timber rocking-wall design

At the core of the Tallwood building was the rocking-wall lateral system: a solid-wood wall panel anchored to the ground using steel cables or rods loaded with large tension forces. Engineers call this a “post-tensioned” design. When subjected to lateral movements, the post-tensioned panel is designed to rock back and forth – absorbing, and thus reducing, the earthquake impact. When the earthquake passes, the tensioned steel rods pull the building back to plumb.

The Tallwood system was designed for “resilient performance,” which means no structural damage from design-level earthquakes and quickly repairable damage after rare but stronger earthquakes.

“Traditional wood-based lateral systems achieve ductility by allowing the structure's connecting elements to deform, which leads to hardware or wood material damage,” Pei explains. “The mass-timber rocking wall is different: the rocking mechanism and sacrificial energy dissipation devices are used to achieve ductility. That is why the wall experiences no damage after so many earthquakes.”

Other Tallwood innovations included a gravity-framing system that ensures low damage under heavy vertical loads, including building weight; and a suite of non-structural elements, including stairs, that can withstand the building’s drift during an earthquake.

The three-year research project culminated with a series of shake table tests at the NHERI at UC San Diego facility. After 88 simulated earthquakes, the Tallwood building suffered no detectible structural damage, revealed by more than 700 channels of wired sensors.

Getting a successful innovation adopted into building code — where the new design can be used by architects and designers with confidence – is the holy grail for research engineers.

Currently, Shiling Pei and his team at Mines are working with the KPFF Consulting Engineers, a long-term project partner, to prepare the Tallwood rocking-wall lateral system for inclusion in ASCE-7, the American Society of Civil Engineers building code that covers natural hazards, including earthquakes. The next ASCE-7 revision is slated for 2028.

Funding for this crucial phase comes from the Charles Pankow Foundation and the U.S. Forest Services – two groups familiar with the complexities of the ASCE code adoption process and with wood-based structural design.

Tasks underway include completing a FEMA P695 study on Tallwood’s mass-timber rocking wall lateral system, a necessary step to document how the design meets seismic performance guidelines. Concurrently, the Mines team is conducting extensive numerical analyses necessary to verify the rocking wall lateral system performance for a wide range of realistic building archetype configurations ranging from 3 to 18 stories.

“While codification can take some time, it’s important to keep in mind that we can design and build resilient tall wood buildings today,” Pei emphasized. “It is a race against time to use our technical know-how to improve seismic resilience for our stakeholders and communities before the next “big one” hits. When we have the technology to make people safer in earthquakes, it becomes an ethical obligation to pursue it. My future plan is what I call “Vision 10 by 2030,” which is trying my best to push for building 10 resilient mass timber buildings in high seismic regions by 2030.”

Related Links

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NHERI Tallwood project page at the Colorado School of Mines, including ASCE codification updates.

Watch: Timelapse video of Tallwood construction at NHERI UC San Diego.

Watch: Tallwood building subjected to 6.7 magnitude Northridge earthquake (1994) on the UCSD shake table, May 9, 2023.

Watch: Tallwood building subjected to 7.7 magnitude Chi Chi earthquake (1999) on UCSD shake table, May 9, 2023.