Mass timber is moving into the high-rise market. Updates to U.S. building codes now permit taller mass timber structures, and developers are responding with projects that reach ten, twelve, and even eighteen stories in some jurisdictions. That growth raises a direct engineering question: how do these buildings perform in a major earthquake? For existing structures, engineers have long applied structural strengthening methods for seismic upgrades, but the lateral systems used in today’s tall timber buildings are new enough that their behavior has to be proven rather than assumed. Full-scale testing is how the industry is answering that question.
The Natural Hazards Engineering Research Infrastructure (NHERI) TallWood project sits at the center of that effort. Funded by the U.S. National Science Foundation, the research program has been simulating a series of large earthquakes on a full-scale ten-story mass timber building, the tallest full-scale structure ever tested on an earthquake simulator, or shake table. The tests took place at the University of California, San Diego, and the data will shape code provisions and design practice for tall timber construction.
How a Ten-Story Timber Building Survives an Earthquake
The specimen was designed by a team of researchers and practitioners around a mass timber rocking wall lateral system suited to regions with high seismic hazard. The design goal is resilient performance: minimal damage under design-level earthquakes and quick repairability after rare events.
The Rocking Wall Lateral System
The rocking wall system is straightforward in concept. Solid wood wall panels are anchored to the foundation with steel cables or rods held under large tension. When lateral forces hit the building, the panels rock back and forth like a metronome, which dissipates energy and limits the forces transmitted to the rest of the structure. Once the ground motion stops, the tensioned steel pulls the panels back to plumb.
Self-Centering After the Shake
This self-centering behavior keeps the building close to its original position after a quake. Conventional walls often end up with a permanent lean and cracked connections that are expensive to straighten. A rocking wall returns to vertical, leaving repair crews with cosmetic work instead of structural re-alignment. The post-tensioning acts like a rubber band returning to its resting length, but with forces measured in hundreds of tons.
The structure is only half the challenge. Because the building rocks during an earthquake, the envelope must tolerate movement without tearing. Air barriers, window flashings, and panel joints all have to survive interstory drift, which is why air leakage testing of the building envelope has become part of the commissioning conversation for tall timber projects.
Full-Scale Shake Table Testing: How Seismic Experiments Work
The tests ran on the outdoor shake table at UC San Diego’s Englekirk Structural Engineering Center, one of the two largest earthquake simulators in the world. The platform has the largest payload capacity of any shake table, capable of carrying structures weighing roughly 2,000 metric tons while reproducing the motions of real earthquakes.
Reproducing Real Ground Motion
Actuators under the platform push the specimen in six degrees of freedom, translating and rotating it to match recorded accelerograms from actual earthquakes. Researchers scale those records to represent design-level and rare events, then measure the building’s response with accelerometers, displacement transducers, and strain gauges mounted on every floor.
The program is setting records of its own. Construction worldwide has been on a record-setting run, with 2019 posting a new record for supertall building completions, and structural research is keeping pace: this ten-story timber specimen is the tallest full-scale building ever tested on a shake table.
| Validation method | What it measures | Relative cost | Typical use |
|---|---|---|---|
| Full-scale shake table test | Complete building response, including nonstructural systems | Highest | Code validation, research benchmarks |
| Reduced-scale shake table test | Global behavior and failure modes | Moderate | Parametric studies, concept screening |
| Component and subassembly tests | Connection and wall panel performance | Low | Detail development, product qualification |
| Nonlinear computer simulation | Predicted response across many ground motions | Lowest | Design, fragility and collapse assessment |
Nonstructural Components: The Hidden Seismic Risk
Resilient design has to account for more than the gravity and lateral frames. Nonstructural components, the systems that are not part of the load-resisting structure, carry much of a building’s function and its ability to recover after an earthquake. Facades, interior walls, and stairways are the components that occupants and first responders depend on first.
Safety-Critical Assemblies Between Floors
The TallWood specimen includes four exterior facade assemblies, a set of interior partition walls, and a ten-story stair tower. These components span from floor to floor, so they are subjected to the relative movement between stories during shaking.
- Exterior facade assemblies with different cladding and glazing configurations.
- Interior partition walls that run continuously through the structure.
- A full-height stair tower with landings, guardrails, and door hardware.
- Utility chases that cross movement joints between floors.
Details That Accommodate Interstory Drift
The facade and stair details were designed with movement capacity in mind, and many of these connections had never been tested in a rigorous building setting before this project. The exterior envelope has to keep out temperature extremes and weather events while the building sways, and the stairs have to stay walkable so occupants can exit and responders can reach every floor.
That combination of weather resistance and movement tolerance is exactly what modern drainage plane assemblies are built for. Facades rely on weather-resistive barriers installed with flexible flashings, lapped joints, and sealant details that are designed to stretch rather than tear.
Fire Resistance and Life Safety in Mass Timber
Tall timber also has to answer the fire question. Building codes treat mass timber as combustible construction, so tall projects pair the wood structure with automatic sprinklers, protected egress paths, and fire-resistance-rated assemblies between compartments.
How Charring Protects the Structure
Large timber members have an inherent defense: a predictable char layer. When exposed to fire, the outer surface of a wood member burns and forms an insulating blanket that slows heat transfer to the remaining cross section. Engineers size members with a sacrificial char zone so the load-bearing core survives the rated fire duration.
Ratings are verified through standardized furnace tests, and designers select assemblies against published fire-resistance ratings that cover walls, floors, and columns. The same standards and testing methods used across commercial building design apply to mass timber elements.
Protected and Exposed Timber
Code paths differ depending on whether timber is left exposed or encapsulated. Encapsulation with multiple layers of gypsum board extends the time before charring begins, which lets designers show more wood while still meeting the required rating.
| Property | Mass timber | Steel | Concrete |
|---|---|---|---|
| Structural weight | Lightest of the three | Moderate | Heaviest |
| Embodied carbon | Stores carbon over the building life | High manufacturing emissions | High cement emissions |
| Fire behavior | Chars at a predictable rate | Weakens at high temperature | Spalls but retains strength |
| Erection speed | Prefabricated panels, few crane picks | Shop fabrication, many connections | Formwork and curing time |
| Seismic mass | Low mass reduces base shear | Moderate mass, ductile frames | High mass increases seismic demand |
Building Codes for Tall Timber Construction
Code changes opened the door for tall timber. The 2021 International Building Code added tall mass timber provisions that permit buildings up to 270 feet, roughly eighteen stories, for the two highest types, and up to 180 feet for a third type, provided the projects meet enhanced fire and structural requirements.
What the Code Requires
These tall wood types come with conditions that go well beyond the base code:
- Automatic sprinkler protection throughout the building, including attics and concealed spaces.
- Noncombustible protection of connections and enhanced diaphragm detailing.
- Encapsulation of structural timber where the assigned building type requires it.
- Fire-resistance-rated exit stairs and horizontal assemblies.
- Additional special inspection requirements during construction.
How Testing Feeds Future Codes
The shake table data feeds directly into this process. Research results help code committees calibrate the height limits, connection rules, and repairability expectations that govern tall timber, so the record-setting test is not just a demonstration; it is an evidence base for the next code cycle.
Site Evaluation and Quality Control From the Ground Up
Seismic performance is decided long before the first panel is lifted. Site conditions, material quality, and installation discipline determine whether a design that works on paper works in the ground.
Quality Control During Erection
Timber arrives with a specified moisture content, and crews check it on delivery and again after panels are exposed to weather. Connection torque, bolt pretension, and grout integrity are verified as erection proceeds. Many tall timber designs pair wood with a concrete core or podium, and the concrete testing methods used on site follow the same field and laboratory procedures applied to any high-rise concrete work.
Geotechnical and Site Testing
The foundation story starts with the ground itself. Soil bearing capacity, groundwater levels, and drainage all influence how the rocking wall anchors perform. Sites with on-site wastewater systems need additional verification, and perc testing and well testing establish soil permeability and water quality before construction begins.