Mass Timber Tower Survives Earthquake Test at UC San Diego

Last year saw a surge of interest in wooden buildings as an alternative to concrete, which when it is manufactured in 2,000-degree kilns contributes an estimated 8% of global greenhouse gas emissions.

Several projects pushed the envelope of mass timber towers up past 20 stories.

Proponents of wood towers got some good news from San Diego this month when a 10-story test tower made out of wood withstood a test that addresses a major concern on the West Coast: a simulated earthquake.

At a unique outdoor test site in Scripps Ranch, UC San Diego has built a test pad that can mimic the impact of some of the worst earthquakes ever recorded—those with epicenters closest to the surface—by shaking whatever structure is built on it.

In a recent test, a 10-story tower primarily made out of cross-laminated timber withstood a simulated 7.7-magnitude earthquake, affirming a belief by engineers who design wood towers that these structures can be safely used as residential or office buildings, the San Diego Union-Tribune reported.

The experiment was led by the Colorado School of Mines (CSM), which is a regular user of what they call the “shake table” at Scripps Ranch, the report said.

The CSM engineers monitoring the test at the UC San Diego test pad, said the building did not appear to suffer any structural damage during the shaking, which in a video of the test shows the tower swaying.

To put this in perspective, the engineers said the shake given to the wooden tower replicated an earthquake that killed more than 2,000 people and destroyed 10,000 buildings in Taiwan in 1999. The 10-story test building was the tallest structure to date to be tested by a shake of that magnitude.

The test team also tested the wooden tower with a simulation of the Northridge earthquake in Southern California, a 6.7-magnitude shake that killed 60 people and caused $13B in property damage in 1994.

“The building performed exactly like we expected,” Shiling Pei, a CSM engineer and the project’s co-director, told the Union-Tribune. “The building should go back to plumb. We designed everything to be elastic like a spring or a rubber band. You can stretch it but it will come back.”

Pei estimated that the top of the test building moved 1 to 2 feet on each side during the most intense shaking.

A 25-story building known as The Ascent, which was completed last year in Milwaukee, is the tallest mass timber structure in the world to date.

The 493K SF, 259-unit residential tower in Milwaukee’s East Town neighborhood offers spectacular views of Lake Michigan, a pool on the sixth floor and a top floor amenity level.

Before The Ascent was constructed, the developers worked with the USDA’s Forest Products Laboratory to complete the world’s first three-hour column fire testing program for glulam columns.

The mass timber residential floors in The Ascent are constructed above five levels of concrete parking garage. A system of glue-laminated timber (glulam) beams and columns support cross-laminated timber (CLT) floors. Two concrete cores provide lateral stability.

According to the architects, an efficient system of post-tensioned concrete beams transfer loads from the timber residential floors to the concrete garage structure below. The superstructure is supported on concrete-filled steel pipe piles—the highest-capacity piles yet built in Wisconsin.

The use of sustainable mass timber allowed The Ascent to exceed Milwaukee’s energy conservation code requirements.