The latest test for timber: how do 10-story structures handle earthquakes?

“We’ve just seen the results of the world’s first ever earthquake simulation on a 10-story timber building. The result? A resounding success.”

The whole area of seismic resistance is rife with myths that cast doubt on wood’s capacity to function satisfactorily in the case of an earthquake. However, its ductility enables it to bend without breaking, taking in and dispersing the energy created by movement and shaking. Also (unlike steel or concrete) wood is a lightweight material that provides a great strength-to-weight ratio, which allows it to endure seismic pressures without adding too much weight to the structure.

This has been thoroughly validated in smaller-scale buildings all over the world. But the question on many people’s lips, now that the idea of mass timber as a way to diminish construction’s carbon footprint is catching on, is this: how does a high-rise mass wood building respond to an earthquake? It turns out the answer to that question is: very well!

To remove any misgivings, the Tallwood Project has constructed a 10-story cross-laminated timber (CLT) structure at the University of California, San Diego (UCSD). The construction was tested on a shaking table that imitated the magnitude 6.7 Northridge earthquake in Los Angeles in 1994 and the magnitude 7.7 Chi-Chi earthquake in Taiwan in 1999.

Because of their lower levels of embodied energy, mass timber structures, which are made with layers of wood linked together, are becoming more frequent in cities across the world. This is notably true in certain US jurisdictions where changes to the International Building Code (IBC) have allowed for gradual increases in the heights of these structures. The changes now include specific design and construction criteria, as well as fire resistance, load capacity, and seismic protection requirements.

The US National Science Foundation (NSF) has committed $17 million to update the world’s biggest outdoor earthquake simulator in order to collect concrete data and test a seismic design technique for tall timber buildings. This shake table, measuring 25 x 40 feet, is part of the NSF’s Natural Hazards Engineering Research Infrastructure network and can hold and shake buildings weighing up to 2,000 metric tonnes or 4.5 million pounds, which is comparable to 1,300 family vehicles. The simulator correctly reproduces all six degrees of freedom of movement encountered during earthquakes: longitudinal, lateral, vertical, roll, pitch, and yaw.

The Tallwood Building, designed by LEVER Architecture and built by Timberlab from donated mass timber products, stands 116 feet tall. According to LEVER “The design […] is distinguished by its mass timber rocking walls, which allow the structure to rock and recentre itself during an earthquake, with no damage to the primary structural system […] The concept exceeds basic life-safety performance requirements by creating a resilient and easily repairable solution, avoiding the need to tear down the building following an earthquake.”

During the testing, 800 sensors captured critical data that will be used to generate and calibrate computer models that will assist engineers in designing comparable buildings in the real world. The top four stories will now be demolished for additional testing aimed at reusing the material when it reaches the end of its useful life.

These results confirm mass timber’s usefulness in construction yet again, and should give all of us pause for thought about whether the projects we’re working on could be better – safer, more environmentally friendly, and better for health and wellness – with the application of more timber.

If you want to discuss your latest project and figure out what species of timber would suit it best – or if you already know what you want and are looking for a quote – give Quercus a call on 0845 50 50 311.