The TallWood project is testing an earthquake-resistant structure

Researchers are redefining structural resilience this month by testing the first 10-story TallWood building made of collective wood and vibrating walls on a vibration table at the University of California, San Diego.

Written by Montana Denton, science writer (@montana_denton)

Quote from: Denton, M., 2023, TallWood Project Tests Structure Resistant to Earthquake, Temblor, http://doi.org/10.32858/temblor.309

Earthquake simulations began today at this 10-story building in TallWood, which was built with block wood and a unique vibrating wall system designed to withstand earthquakes. Credit David Baillot, Jacobs School of Engineering, University of California San Diego, CC BY 2.0

Timber block may just be the building material of the future, and it is growing in popularity due to its predictable sustainability and energy efficiency. But whether it stands up to the most severe structural test of all – earthquakes – remains to be seen. Shilling Bay, assistant professor of engineering at the Colorado College of Mines, wants to find out.

To that end, the Pei-led TallWood Project, funded by the National Science Foundation, aims to investigate the resilience of residential and mixed-use wood buildings this month by simulating a series of large earthquakes on a 10-story log building—the tallest full-size building ever tested by an instrument. earthquake simulation.

Timber is not directly from trees

Massive log buildings use solid or engineered wood as the primary component of the construction. Unlike lumber harvested directly from trees, block lumber are paneled, solid wood products that are often reinforced—in this case, with cross-laminated lumber (CLT)—to improve structural performance. The material is gaining popularity as a building component and could offer a more sustainable alternative to traditional building materials such as steel and concrete.

Shiling Pei and colleagues are testing the response of wood mass to earthquakes on a vibration table at the University of California San Diego. Credit: David Pilot, Jacobs School of Engineering, University of California San Diego, CC BY 2.0

“The marvel of this test is not just an improvement in our understanding and confidence in seismic design principles, but its potential to open up entirely new possibilities for sustainable design,” says timber expert and structural engineer Greg Kingsley. Kingsley, CEO of Colorado-based KL&A Engineers and Builders, brings his industry expertise to the School of Mines’ collegiate lumber endeavor, revising TallWood drawings for basic stability and completeness. He explains that to create more climate-friendly buildings, engineers must focus on reducing the overall carbon footprint of the built environment. Proponents of mass construction of timber argue that wood buildings have much lower emissions than concrete and steel alternatives; The wood used in these buildings also stores carbon, providing a green, renewable and often more cost-effective building material.

TallWood also tests a unique swing wall system that involves large planks of wood held together by steel cables or rods with significant tension forces. These panels should allow the walls to be more flexible and to sway back and forth during earthquakes but not collapse. Credit: David Pilot, Jacobs School of Engineering, University of California San Diego, CC BY 2.0

Rocking walls

Kingsley says the TallWood test “is a comprehensive and unprecedented seismic simulated test on a timber building,” but it is also a test of a unique vibrating wall system.

Bay explained in a press release that the swing wall system, which consists of a solid wood wall panel that is fixed to the ground using steel cables or bars with large tension forces, is intended to reduce collapse risks and reduce seismic damage. “Exposed to lateral forces, the wooden wall panels will sway back and forth – reducing the effects of the earthquake – and then the steel bars will pull the building into its lofty position once the earthquake has passed.”

Kingsley says this lateral load-bearing system is not currently incorporated into building codes. However, the load-bearing system has the potential to augment the benefits of constructing buildings of several stories with massive timbers, called “tall logs” (hence the name of the subject matter of this news story).

The testers hope the swing wall system will help protect non-structural components in buildings, such as staircases, during earthquakes. Credit: David Pilot, Jacobs School of Engineering, University of California San Diego, CC BY 2.0

Such a system is also likely to protect non-structural components within the building — such as stairs — that would be expected to experience noticeable movement during seismic simulations. In the reality of an actual earthquake, these components must be protected by the building’s exterior envelope to maintain the functionality of the interior, allowing safe egress and efficient access for the first responder.

seismic simulation

Earthquake-ready renovations can be tested with UCLA’s NHERI Large High-Performance Outdoor Vibration Table (LHPOST), which tests the seismic resilience of structures built upon. As part of the National Science Foundation’s nationwide earthquake engineering collaboration effort, the site shakes large-scale structures under realistic seismic conditions. Capable of shaking structures up to 2,000 metric tons, the table has the world’s largest load capacity compared to other earthquake simulators. Recent upgrades mean it can synthesize the same 3D ground motions that occur during earthquakes – when the ground undulates up and down, back and forth, and left to right, while also spinning (rotational motions are called rolling, tilting and yawing).

LHPOST has updated building codes and validated new technologies, and can help organizations like CalTrans, FEMA, and the Department of Energy collect critical data for construction. It also provides research groups like Pei with the ability to build full-scale facilities to develop more earthquake-resistant infrastructure.

In 2017, Pei’s team built a huge two-storey wooden building in NHERI LHPOST. The team tested their construction by simulating shaking from the Northridge earthquake, a 6.7-magnitude quake that struck Los Angeles in 1994. The building sustained virtually no structural damage after grueling testing, providing evidence of the earthquake-resistant ability of wooden buildings.

The TallWood Test Building is under construction. It’s the first full 10-story building to rock UCLA’s NHERI Big Outdoor High Performance Table in San Diego. Credit: Shiling Pei/Colorado School of Mines

TallWood test

The next step is to test a tall wooden building. Pei’s TallWood is the first chassis to be tested on the new and improved vibrating table. The project, led by the School of Mines, has been constructed at the site in San Diego, Pai says, and testing began today. The tests simulate seismic motions recorded during previous earthquakes – including Northridge’s – and will cover a range of magnitudes, from magnitude 4 to magnitude 8. The simulation is based on the subsurface testing as if the building were constructed in the Capitol Hill neighborhood of Seattle.

During the testing weeks, the Pei team starts with low levels of vibration and will gradually increase the intensity over the course of the trial. The TallWood building is equipped with 800 cable sensors and about 60 video cameras to capture how seismic damage occurs to the structure and how it responds as tremors increase in strength. You can see some of the tests here.

The unpredictability of earthquakes requires constant human innovation—creating structures that are stronger, safer, more sustainable, and more stable. “The strength and character of earthquakes is inherently unknown, and site conditions are quite variable around the world, so the best we can do is minimize the potential for damage or collapse — hopefully very large,” says Kingsley. Moreover, the TallWood test may change the future of building construction, he says. “[This test] It could make the design of wooden high-rise buildings more economical and more flexible, which would then have the broader effect of increasing options for reducing the embodied carbon footprint of mid-rise buildings. ”

Vibrating walls were installed in the TallWood test building prior to its construction last year. Image credit: David Baillot, Jacobs School of Engineering, University of California San Diego, CC BY 2.0 References

Wichman, S., Berman, JW, and Pei, S., 2022, Experimental investigation and numerical modeling of cross-linked laminated timber walls on an elastic basis, earthquake engineering and structural dynamics, https://doi.org/10.1002/eqe.3634

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