The tallest steel structure ever tested on a seismic simulator slowly swayed, rocked, and twisted during the experiment. This 10-story, approximately 30-meter-high building is being subjected to real earthquake scenarios, including the 1989 magnitude 6.9 Loma Prieta earthquake. The test is part of research to determine whether height restrictions for cold-formed steel (CFS) buildings can be increased.

The testing is taking place on the seismic simulator (shake table) at the University of California San Diego, funded by the U.S. National Science Foundation. It is one of the three largest shake tables in the world and the only one located outdoors—an essential feature for testing buildings that exceed height limits. In fact, it is the only facility globally capable of testing structures taller than approximately 27m. Two years ago, researchers used this table to shake a ~35-meter-tall mass-timber building—the tallest structure ever tested on a seismic simulator at that time.

This year's focus is on cold-formed steel (CFS) construction. CFS is a lightweight, sustainable, and non-combustible material, with 60–70% recycled metal content. Current building codes limit such structures to about 19m (six stories), but researchers are investigating whether this can be raised to 10 stories (~30m), even in seismically active regions. Current test results indicate it is feasible.

Project leader Tara Hutchinson, professor in the Department of Structural Engineering at UC San Diego, said: "The building performed exceptionally well. Despite undergoing 18 earthquakes of progressively increasing intensity—including three that exceeded the levels considered by design engineers—the load-bearing structural system remained intact." However, some damage to non-structural components was expected. The stairwells were designed to move with the building and remain usable.

Hutchinson also noted that nearly 1,000 sensors were installed throughout the building to measure responses in acceleration, displacement, and local strain. The resulting data will help refine building codes and support the construction of taller, lighter, and more resilient structures using this high-quality material. Because CFS is lightweight, it can be prefabricated into modular units and assembled like giant Lego blocks, significantly reducing construction time compared to building a frame from scratch. Hutchinson believes CFS offers numerous advantages that will benefit community resilience in the future.

These tests also highlight the importance of the major upgrade to the NSF-funded shake table. The $17 million upgrade, completed in April 2022, enables six-degree-of-freedom motion—the table previously moved only east-west but can now also move up-down, north-south, and perform roll, pitch, and yaw. In this test series, the team used the same earthquake records but tested the building in one-, two-, and three-dimensional motion by selectively disabling degrees of freedom.

Joel Conte, professor of structural engineering at UC San Diego and one of the shake table's principal investigators, explained that historical earthquake records show the ground does not shake in just one direction—it moves back and forth, up and down, side to side, and even twists. The upgrade allows simulation of "near real-world" earthquake conditions. During the June 23 test, researchers observed a certain degree of torsional motion in the building—something that would not have occurred when the table could only move in one direction. Ben Schafer, professor of engineering at Johns Hopkins University and co-principal investigator of the CFS10 project, said the observed motion demonstrates the critical importance of the table upgrade for scientific research.

The test series is not yet complete. In addition to carefully examining the building's physical condition after the earthquake tests, the team is preparing for the final phase of live-fire testing later this month. These fire tests, led by Professor Richard Emberley from California Polytechnic State University, San Luis Obispo, aim to understand how temperature, smoke, and particulates spread in earthquake-damaged areas of the building—i.e., "post-earthquake fire" scenarios that can be triggered by gas leaks or other hazards. Hutchinson noted that, unlike wood and other materials, light-gauge steel framing is non-combustible—an important advantage when fire is a concern.