How A 10 Story Wood Building Survived More Than 100 Earthquakes

One sunny morning last month, an earthquake jolted northeast San Diego. Minutes later, another earthquake hit, causing a 10-story wood building to sway. A computer triggered the quakes, and the shaking was confined to a 1,000-square-foot platform on which the building -a full-size test model -stood. It is the tallest structure ever subjected to simulated earthquakes on the world’s most enormous high-performance “shake table,” which uses hydraulic actuators to thrust the steel platform through six degrees of motion to replicate seismic force. The structure is the centerpiece of the NHERI TallWood project, which seeks to answer whether multi-story buildings built of wood can withstand large, destructive quakes.

The simulated quakes were designed to simulate those recorded in Northridge and other California locales. The researchers wanted to see how the building, constructed from mass timber – layers of wood bonded together – would fare under different conditions. So the researchers first tested the skeleton of the building, then outfitted it with walls sheathed in gypsum board and standard features like windows, doors, stairs, and interior insulation. The team also incorporated various nonstructural components to see how they would perform during an earthquake, such as flooring and ceilings.

The building’s wooden skeleton is made from cross-laminated timber, or CLT – a renewable material that offers more strength than concrete and more flexibility than steel, says NHERI project co-principal investigator Shiling Pei and Colorado School of Mines associate professor. The material is particularly well-suited to seismic events because of its natural flexibility, which resembles how tree branches bend without breaking. “With this design, we’ve tried to take advantage of this property and make the building as flexible as possible,” he says.

This flexing allows the building to absorb and dissipate seismic energy rather than transferring it to other structures or people inside, which can be deadly in an earthquake, Pei says. The building also incorporates a series of curved braces called glulams, which run throughout the structure to help distribute forces evenly and further mitigate damage.

The researchers’ next step is to test the building again, but this time, it will be fully furnished and fitted with additional nonstructural elements like flooring and ceilings. The team will then re-enter the building and subject it to synthetic earthquakes similar to those recorded in Northridge and elsewhere to understand how the wood structure reacts when fully outfitted with standard features.

The results will reveal whether the building, based on designs for a 10-story apartment complex in Seattle’s Capitol Hill neighborhood, can withstand a significant earthquake in real life. Pei and his colleagues are confident it can, but they want to show the broader community that multi-story wood construction is a viable alternative to concrete and steel. The NHERI TallWood research could lead to a wood-framed multi-story building in an actual city in 2023.