In earthquake-prone Seattle, developer Wright Runstad & Co. announced the start of construction of Rainier Square Tower, an office-residential high-rise that represents the first use of a radically different core structure. Called a coupled steel-plate composite shear wall because its cross-tied plates, like bread slices, are filled with rebar-free concrete, the core is engineered to be simpler, faster and safer to construct than a reinforced-concrete core plagued by rebar congestion, says the job’s structural engineer, Magnusson Klemencic Associates (ENR 10/9 p. 8). General contractor Lease Crutcher Lewis plans to build a mock-up of the core to work out the construction details. If all goes according to plan, the superstructure of the tower, designed by architect NBBJ, will top out in mid-2019. Amazon, which signed a lease for the 722,000-sq-ft office portion, is expected to move in during 2020.