10-story Steel-framed Building to be Put to the Test on UC San Diego Earthquake Simulator

10-story Steel-framed Building to be Put to the Test on UC San Diego Earthquake Simulator

The Big Shake: How the World's Largest Earthquake Simulator Is Rewriting Building Codes

A 10-story wooden skyscraper survives humanity's most powerful artificial earthquakes, proving that our assumptions about seismic safety may be dangerously outdated

On a sunny Tuesday morning in May 2023, something unprecedented happened in San Diego. A 113-foot-tall wooden building—taller than the Statue of Liberty's pedestal—swayed violently back and forth, up and down, and side to side as the ground beneath it lurched with the fury of some of history's most devastating earthquakes. When the shaking stopped, the building stood unharmed.

This wasn't a natural disaster. It was science in action at the University of California San Diego's massive earthquake simulator, and the results are forcing engineers to completely rethink how we build in earthquake country.

The Machine That Shakes Mountains

Picture a concrete platform the size of a basketball court that can hurl 4.5 million pounds—roughly the weight of 1,300 cars—through the air with the precision of a Swiss watch. When reproducing a large earthquake, the power delivered by the shake table is about 9 MW, corresponding to the daily peak power consumption of a small town of a few thousand households.

This is UC San Diego's Large High-Performance Outdoor Shake Table, known to researchers as LHPOST6, and it's the closest thing we have to bottling up an earthquake and releasing it on demand. Unlike every other major earthquake simulator in the world, this one sits outdoors under the California sun, meaning there's no ceiling to limit how tall the structures it can test.

For nearly two decades, this mechanical marvel has been putting buildings, bridges, and other structures through their paces, simulating everything from gentle tremors to catastrophic quakes. Tests here have resulted in changes to building codes for everything from hospitals, to tall buildings, to roads and bridges.

But until recently, the shake table had a major limitation: it could only move back and forth in one direction, like a massive, single-axis washing machine. Real earthquakes, however, are far more chaotic. During the 1994 Northridge earthquake in the Los Angeles area, bridge columns punched through bridge decks, hinting at a strong vertical ground motion. Similarly, during the 1971 San Fernando earthquake, the buildings twisted and swayed, hinting that the ground was probably rotating.

That changed in 2022 when a $17 million upgrade transformed the facility into a six-degree-of-freedom monster capable of reproducing the full, terrifying complexity of earthquake motion. It went from being able to move in one direction – east-west – to three directions – east-west, north-south, up and down, as well as roll, pitch and yaw, three motions in the x, y and z axes performed by airplanes in flight and commonly seen in earthquake motions.

The Wooden Giant That Shouldn't Work

The first test subject for the newly upgraded shake table was audacious: a 10-story building made almost entirely of wood. In an age when skyscrapers are built from steel and concrete, the idea of constructing a 113-foot-tall wooden building in earthquake country seems almost quaint—or dangerously naive.

Engineers gathered on May 9 to shake a 10-story mass timber building–the tallest full-scale building to be tested on an earthquake simulator. This wasn't just any wooden building. It was constructed using cross-laminated timber (CLT), an engineered wood product created by gluing layers of lumber at right angles to create panels that are stronger than steel in some applications.

But the real innovation wasn't in the materials—it was in the design philosophy. Traditional earthquake-resistant buildings are designed to absorb earthquake energy by allowing certain parts to break in a controlled way, like crumple zones in a car. The wooden giant, however, was designed around a radical concept: what if a building could rock back and forth like a rocking chair, dissipating earthquake energy without sustaining any damage at all?

The building's secret lay in its "rocking walls"—massive timber panels connected to the foundation with steel tendons that work like giant rubber bands. Featuring a rocking wall system, the building's wood wall panels are anchored down by steel rods, designed to create a more seismic resilient structure. The panels rock back and forth, reducing the earthquake impact. The tension of the rods helps bring the building back to plumb.

Surviving the Impossible

The testing protocol was brutal. A total of 88 earthquake tests at different intensity levels were conducted, including several at the risk targeted maximum considered earthquake intensity for the building's design location. The building was subjected to recreations of some of history's most destructive earthquakes, including the 6.7-magnitude Northridge quake that killed more than 50 people in 1994, and the devastating 7.7-magnitude Chi-Chi earthquake that struck Taiwan in 1999.

There were over 800 sensors deployed on the 10-story tower, which provide data needed to help design buildings that are safer in strong earthquakes and to make changes in design codes for commercial and residential structures. High-speed cameras captured every movement, while accelerometers measured forces that would crush a human body.

The results defied expectations. "It performed exactly as we expected — the building remained damage free after two major design-level earthquakes back to back," said Shiling Pei, associate professor at Colorado School of Mines and lead investigator on the NHERI Tallwood Project.

Not only did the building survive—it thrived. There was very, very minimal damage, and that damage was more cosmetic. Like you could just repair it easily and move on. After more than 100 simulated earthquakes over three months of testing, the wooden skyscraper showed virtually no structural damage.

Rewriting the Rules

The implications of these tests extend far beyond one experimental building. They're forcing a fundamental reconsideration of how we approach earthquake safety, particularly as climate change drives demand for more sustainable building materials like mass timber.

Building codes will likely be changing soon, following the shake table experiment But the changes go beyond just wooden buildings. Recent tests at UC San Diego have identified problems with steel columns commonly used in California buildings. An 18-foot steel column shakes in the grip of a vise on UC San Diego's shake table. The column would stand vertically in a building, and the shake table stimulates the stress of a building's weight and the movement of a strong earthquake. Ultimately, the column buckles and bends, which could cause a structure to lean or even collapse.

These discoveries highlight a troubling reality: many of our building codes are based on educated guesses rather than comprehensive testing. "A lot of current design provisions are based on scaled-down column tests or a very small number of full-scale tests. The UC San Diego facility is changing that by enabling full-scale testing that reveals problems invisible in smaller experiments.

The Science of Staying Upright

What makes the wooden building's performance so remarkable isn't just that it survived—it's how it survived. Traditional seismic design accepts that buildings will be damaged in major earthquakes, focusing on preventing collapse and protecting lives. But the rocking wall system demonstrated something different: the possibility of "earthquake-proof" buildings that emerge from major seismic events ready for immediate reoccupancy.

At a high level, this new type of lateral-force-resisting system has proven to be perhaps one of the most structurally resilient building systems ever developed. The secret lies in the system's ability to convert the destructive horizontal forces of an earthquake into a gentle rocking motion, like a ship riding out a storm.

The building's designers incorporated specially designed U-shaped metal plates that bend and flex to absorb energy, concentrating any potential damage into easily replaceable components. Meanwhile, the building's post-tensioned cables—essentially giant guitar strings made of steel—provide the restoring force to pull the structure back to vertical after each earthquake pulse.

Beyond Buildings: A New Paradigm

The research at UC San Diego represents more than just better buildings—it's pioneering a new approach to resilience thinking. "With this data, the researchers are able to develop, calibrate and validate the computational model that engineers in the real world use to design buildings and bridges and so on," said Conte.

This matters because modern building design increasingly relies on computer simulations to predict how structures will perform in earthquakes. But those simulations are only as good as the data used to create them. The 6-DOF capabilities will enable researchers to develop, calibrate, and validate predictive high-fidelity mathematical-computational models, and to verify effective methods for earthquake disaster mitigation and prevention.

The wooden building project is now driving real-world change. Supported by U.S. Forest Services (Wood Innoations Fund) and CHarles Pankow Foundation, we are conducting a FEMA P695 study to obtain seismic design parameters for the post-tensioned mass timber rocking wall lateral system so it can be included in future ASCE7 as a prescribed lateral system for anyone to adopt.

The Human Element

Behind the technical achievements lies a more fundamental question: How do we balance innovation with safety? Shiling Pei, the project's lead researcher, has spent over two decades studying wood structures. "I've been conducting wood and seismic research for over two decades," says Pei. "The interesting thing about wood is that it is very hard to scale it down for testing. You almost always have to do a full-scale test. It's also more convincing if you can do a full-scale test."

This insight cuts to the heart of earthquake engineering's greatest challenge: the gap between theory and reality. Small-scale models and computer simulations can only reveal so much. Some phenomena only emerge at full scale, under real loading conditions, with real materials and real construction methods.

Shaking Up the Future

The success of the wooden skyscraper experiment is already rippling through the engineering community. January 25, 2024, Engineering News Record: 2023 Top 25 Newsmakers: Shiling Pei: Proved that Resilient Seismic Performance of a Novel Tall-timber Rocking-wall System in Unprecedented Shake-Table Tests

But perhaps more importantly, it's changing how we think about the relationship between sustainability and safety. As cities worldwide grapple with climate change, mass timber construction offers a path toward carbon-neutral buildings. Wood stores carbon that would otherwise contribute to greenhouse gas emissions, and it requires far less energy to produce than steel or concrete.

The challenge has always been convincing regulators and the public that wooden buildings can be safe in earthquake zones. The UC San Diego tests provide compelling evidence that not only can they be safe—they might actually be safer than conventional construction.

The Next Shake

The research continues. Final testing of the Natural Hazards Engineering Research Infrastructure (NHERI) Converging Design Project officially concluded on March 1, 2024. The project evaluated the functional recovery of a six-story mass timber structure, which included Mass Ply Panels by Freres Engineered Wood, by subjecting the specimen to a series of simulated earthquakes on the world's largest outdoor shake table.

Each test builds on the last, creating an ever-growing database of how structures really behave when the earth moves beneath them. "This big machine has contributed to making many of the buildings we live in and the infrastructure we use today safer," said Jacobs School Dean Albert P. Pisano.

As California faces an uncertain seismic future—scientists estimate a 75 percent chance of a major earthquake striking the region in the next 30 years—the work at UC San Diego offers both hope and practical solutions. The massive shake table continues its patient work: shaking buildings to their limits so that when the real Big One comes, we'll be ready.

In a world where natural disasters seem increasingly frequent and severe, the ability to build structures that can literally dance with earthquakes and emerge unscathed isn't just impressive engineering—it's essential for our survival and prosperity. The wooden giant that shouldn't work might just be showing us the way forward.

Seismic Performance Validation at the UC San Diego Large High-Performance Outdoor Shake Table: Advancing Building Codes Through Full-Scale Testing of 10-Story Structures

Abstract

The University of California San Diego Large High-Performance Outdoor Shake Table (LHPOST6) represents a critical advancement in earthquake engineering research, particularly for validating and improving building codes for mid-rise and tall structures. This review examines recent landmark experiments conducted at the facility, with emphasis on the NHERI TallWood Project's testing of a full-scale 10-story mass timber building—the tallest structure ever tested on an earthquake simulator. These experiments have directly influenced building code revisions and established new design methodologies for seismic-resistant construction. The facility's unique 6-degree-of-freedom capabilities and unprecedented payload capacity have enabled comprehensive validation of computational models and design standards that form the foundation of modern seismic building codes.

Introduction

The Challenge of Seismic Building Design

Earthquake engineering faces a fundamental challenge: validating theoretical design approaches against real-world seismic performance. Traditional building codes often rely on scaled-down testing or computational models that may not fully capture the complex system-level behavior of full-scale structures during seismic events. The upgrade of the University of California at San Diego Large High Performance Outdoor Shake Table (LHPOST) funded by the National Science Foundation (NSF) Natural Hazard Engineering Research Infrastructure (NHERI) network from one to six degrees of freedom (6-DOF) is critical for the economical design, construction, and implementation of improved seismic mitigation strategies.

The UC San Diego earthquake simulator, now known as LHPOST6, addresses this critical gap by providing the world's largest payload capacity for seismic testing—The shake table can carry and shake structures weighing up to 2000 metric tons, or 4.5 million pounds–roughly the weight of 1300 sedan cars. This makes it the earthquake simulator capable of carrying the largest payload in the world. This capability enables researchers to test full-scale buildings and infrastructure components under realistic earthquake conditions, providing data essential for validating and improving building codes.

Facility Capabilities and Technical Specifications

Six-Degree-of-Freedom Motion System

When its renovations are complete, the LHPOST6 shake table at UC San Diego will be able to move in all directions: back and forth, up and down, left to right, yaw, pitch and roll. Reproducing earthquake motions in 6-DOF is key because during a temblor, the ground may move in any direction. This upgrade, completed with $17 million in NSF funding, transformed the facility from a single-degree-of-freedom system to the most sophisticated earthquake simulator in the United States.

It went from being able to move in one direction – east-west – to three directions – east-west, north-south, up and down, as well as roll, pitch and yaw, three motions in the x, y and z axes performed by airplanes in flight and commonly seen in earthquake motions. This capability is crucial for realistic earthquake simulation, as during the 1994 Northridge earthquake in the Los Angeles area, bridge columns punched through bridge decks, hinting at a strong vertical ground motion. Similarly, during the 1971 San Fernando earthquake, the buildings twisted and swayed, hinting that the ground was probably rotating.

Research Infrastructure and Impact

Since its commissioning in 2004, the UC San Diego Large High-Performance Outdoor Shake Table (LHPOST) has enabled the seismic testing of large structural, geostructural and soil-foundation-structural systems, with its ability to accurately reproduce far- and near-field ground motions. Thirty-four (34) landmark projects were conducted on the LHPOST as a national shared-use equipment facility part of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) and currently Natural Hazards Engineering Research Infrastructure (NHERI) programs.

The NHERI TallWood Project: A Landmark in Building Code Validation

Project Overview and Significance

The NHERI TallWood Project represents the most comprehensive validation study of tall wood building performance ever conducted. Engineers gathered on May 9 to shake a 10-story mass timber building–the tallest full-scale building to be tested on an earthquake simulator. The test took place at the UC San Diego NSF-funded outdoor shake table, one of the two largest shake tables in the world.

NHERI Tallwood project is an NSF-funded research effort to develop and validate a resilient-based seismic design methodology for tall wood buildings. The project was designed to address a critical gap in building codes for mass timber construction in seismic regions, where traditional design approaches may not adequately account for the unique properties of engineered wood systems.

Experimental Design and Testing Protocol

The 10-story test building incorporated innovative seismic design features that challenge conventional approaches to earthquake-resistant construction. Researchers tested a low-damage lateral system that enables resilient performance, which means the building will have minimal damage from design level earthquakes and can be repaired quickly after an earthquake.

Over a three-year period, academic and industry partners collaborated on the design, construction, and testing of a 34 m (113 ft) tall, 10-story mass timber building at the world's largest outdoor shake table facility (NHERI@UC San Diego). The test building incorporated a resilient mass timber rocking wall lateral system, gravity connection details designed to remain damage-free under design level earthquakes as well as innovative nonstructural systems detailed to tolerate moderate building drifts without significant damage.

The testing protocol was extensive and systematic: A total of 88 earthquake tests at different intensity levels were conducted, including several at the risk targeted maximum considered earthquake intensity for the building's design location. This comprehensive testing regime included simulations of major historical earthquakes, with the first test was the equivalent of the 6.7 magnitude 1994 Northridge earthquake, the second the equivalent of the 7.7 magnitude Chi Chi earthquake that took place in Taiwan in 1999.

Data Collection and Instrumentation

The experimental program generated unprecedented data for building code validation. There were over 800 sensors deployed on the 10-story tower, which provide data needed to help design buildings that are safer in strong earthquakes and to make changes in design codes for commercial and residential structures.

Building Code Validation and Impact

Direct Code Revisions

The research conducted at UC San Diego has resulted in direct changes to building codes. Tests here have resulted in changes to building codes for everything from hospitals, to tall buildings, to roads and bridges. One notable example involved the identification of deficiencies in steel column design. Building codes will likely be changing soon, following the shake table experiment, because the column is used in many California buildings. The experiment are detailed in an article published in The Journal of Structural Engineering.

Computational Model Validation

A critical aspect of building code development is the validation of computational models used in design practice. "With this data, the researchers are able to develop, calibrate and validate the computational model that engineers in the real world use to design buildings and bridges and so on," said Conte.

The upgraded 6-DOF capabilities will enable the development, calibration, and validation of predictive high-fidelity mathematical/computational models, and verifying effective methods for earthquake disaster mitigation and prevention. This capability is essential because building codes increasingly rely on performance-based design approaches that depend on accurate computational modeling.

Mass Timber Building Code Development

The TallWood Project has particular significance for the development of building codes for mass timber construction. TallWood tests showed a viable pathway for "Earthquake-Proof" tall wood buildings. But can a normal design firm do this? Supported by U.S. Forest Services (Wood Innoations Fund) and CHarles Pankow Foundation, we are conducting a FEMA P695 study to obtain seismic design parameters for the post-tensioned mass timber rocking wall lateral system so it can be included in future ASCE7 as a prescribed lateral system for anyone to adopt.

Performance Outcomes and Code Implications

The experimental results have exceeded expectations and challenged conventional assumptions about tall wood building performance. "It performed exactly as we expected — the building remained damage free after two major design-level earthquakes back to back," said Shiling Pei, associate professor at Colorado School of Mines and lead investigator on the NHERI Tallwood Project.

At a high level, this new type of lateral-force-resisting system has proven to be perhaps one of the most structurally resilient building systems ever developed. This exceptional performance has significant implications for building codes, potentially allowing for more efficient designs and reduced seismic design forces for similar systems.

Methodological Advances in Code Validation

Full-Scale Testing Advantages

"I've been conducting wood and seismic research for over two decades," says Pei. "The interesting thing about wood is that it is very hard to scale it down for testing. You almost always have to do a full-scale test. It's also more convincing if you can do a full-scale test. And the only place we can do a 10-story, full-scale test of our design is NHERI's outdoor shake table at UCSD."

Multi-Directional Testing Capabilities

The upgrade to 6-DOF capabilities has enabled more realistic validation of building codes. The TallWood team had previously done a test on a two-story tower in 2017 but could only glean so much about how an earthquake might affect the building elements since the platen could only move horizontally. The enhanced capabilities now allow for comprehensive evaluation of three-dimensional building response.

Future Implications and Research Directions

Broader Infrastructure Applications

Research conducted using the LHPOST6 will improve design codes and construction standards, validate high-fidelity computational models, and develop accurate decision-making tools necessary to build and maintain sustainable and disaster-resilient communities.

The facility's impact extends beyond individual building codes to encompass broader infrastructure resilience. The upgraded shake table is also expected to generate datasets that will help develop, calibrate, and validate physics-based computer modeling and simulation for civil structures and infrastructure systems.

Conclusions

The UC San Diego Large High-Performance Outdoor Shake Table represents a transformative tool for building code validation and development. Through landmark experiments such as the NHERI TallWood Project, the facility has demonstrated the critical importance of full-scale testing in validating theoretical design approaches and computational models that form the foundation of modern building codes.

"This big machine has contributed to making many of the buildings we live in and the infrastructure we use today safer," said Jacobs School Dean Albert P. Pisano. The facility's unique capabilities have enabled direct improvements to building codes for various structural systems and have established new paradigms for resilient design, particularly in mass timber construction.

The research conducted at this facility continues to influence building codes and design standards, ensuring that structures can better withstand seismic events and protect both human life and economic investments. As building technologies evolve and new materials and construction methods emerge, the UC San Diego shake table remains an essential tool for validating their seismic performance and incorporating them safely into building codes.

Acknowledgments

This research was supported by the National Science Foundation through the Natural Hazards Engineering Research Infrastructure (NHERI) network. The authors acknowledge the contributions of the many researchers, engineers, and industry partners who have made these advances in earthquake engineering possible.

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