With one of the first mass

Apr 16, 2023

The Heartwood under construction. It opens for residents soon at 14th and Union. (Image: Timberlab)

(Image: Nheri ESEC)

The eight-story Heartwood is ready to open above E Union as the first one of the first mass-timber highrise apartment building in the United States. Tuesday, University of Washington researchers will conduct a test simulating a major earthquake on Capitol Hill and how a life-size, larger version of a ten-story, cross-laminated timber building holds up to the shaking of "The Big One."

CORRECTION: The Ascent in Milwaukee opened in July 2022.

You can watch the test live and see how the building holds up — or doesn't.

"Mass timber is a new material, so we are testing it in a taller building as a proof of concept and to study if this is actually feasible — there aren't any buildings in the world that are 10 stories and have structural systems made entirely of timber," UW Civil & Environmental Engineering Ph.D. student Sarah Wichman said in the university's announcement about the project.

Unlike the Heartwood which is being readied to open soon for residents at 14th and Union, the test building the UW students are jostling using a giant shake table facility at the University of California San Diego is timber all the way down to its seismic bracing. At Heartwood, the team from DCI Engineers used steel lateral bracing and a concrete foundation to steady the first of its kind building.

But there is evidence that the "ductility" of wood could also help make timber buildings safer during earthquakes. "This means that it is a material that supports a great deal of deformation until the moment of its fracture," ArchDaily reports. "That is, it bends before breaking."

The city's more standard housing stock, meanwhile, will also face a test in a major earthquake. Since 2001's large Nisqually quake, many of the city's buildings have been reinforced like the Piston and Ring preservation-friendly overhaul on 12th. Here's a look at how Capitol Hill's greatest old buildings stand up, with elegance, to earthquakes. But a 2012 survey effort by the city showed Capitol Hill is home to one of the largest clusters of unreinforced masonry buildings in the city.

The city has yet to implement requirements it has been working on for years to mandate quake readiness projects for unreinforced masonry buildings in Seattle. Still, some property owners have moved forward with reinforcement projects as the mandate work continues. In 2013, the city told CHS 14% of all buildings designated as URM structures were undergoing voluntary retrofits. Nearly 20% of Seattle's unreinforced masonry structures were on Capitol Hill, First Hill, and in the Central District.

The results of the monthlong Natural Hazards Engineering Research Infrastructure (NHERI) Tall Wood project-funded test could help usher in more mass timber construction and help make the projects even more sustainable. UW says the researchers are evaluating the performance of two primary types of mass timber, Cross Laminated Timber and Mass Plywood Panels, "which are relatively new to the building scene and are slowly gaining popularity as a greener alternative."

The UW report notes the environmental concerns at the core of the move to explore mass timber construction — the production of concrete is a huge contributor to global carbon dioxide (CO2) emissions. Mass timber has other benefits including local sourcing — all of Heartwood's components, for example, were sourced within a 400-mile radius of the Seattle job site, its developers say.

In San Diego, the test of the more fully timber-based construction will bring some unknowns but the researchers think their designs should hold up to the special shake sessions planned for Tuesday. The researchers say the building they will be testing was "designed to be located in the heart of Seattle — the Capitol Hill neighborhood."

"Seattle was selected due to the city's risk of significant, yet uncommon, seismic events," the researchers asure.

A previous test of a two-story timber building in 2017 which wasn't location-specific was deemed a success.

During the monthlong testing process including Tuesday, a series of earthquakes are being simulated with increasing intensity. The final phase will include ground motions for the maximum earthquakes that buildings are designed for in Seattle, which has two primary faults: The Seattle Fault that runs east-west through the middle of the city, capable of earthquakes up to 7.4 magnitude, and the Cascadia Subduction Zone along the coast, capable of a magnitude 9 earthquake.

CHS reported here in 2021 as the construction permit was issued for the Heartwood. The Community Roots Housing and DCI Engineers project will open soon as affordable workforce housing. As a Type IV-C permitted project, it was allowed to climb to eight stories and have full exposure of its timber beams so residents and visitors can see, touch, and feel the wood. Other types can build higher — like this project on First Hill — but require that the wood be kept more "encapsulated" the taller the building. And, yes, the Heartwood's steel bracing and concrete foundation will also be in place.

You can learn more about leasing options on the soon to open building at heartwoodseattle.com.

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