As predicted, the Erection Co. topped out Seattle’s 850-ft-tall Rainier Square Tower, with its radical composite steel frame dubbed “speed core,” in only 10 months. Steel erection began last October in the lowest basement.

The retail-office-residential building is on course for substantial completion next Aug. 13, according to Andy Bench, project manager for the developer, Wright Runstad & Co.

The core, surrounded by a conventional steel frame, consists of a modular sandwich system of cross-tied steel-plate walls, field-filled with concrete. The modules were fabricated by the Supreme Group. The system requires no rebar and no formwork. The steel erector installed the final core module on Aug. 9.

The overarching aim is to usher in an era of speedier, safer and better office tower construction, compared with concrete core towers with steel perimeter frames. Ron Klemencic, chairman and CEO of the project’s structural engineer, Magnusson Klemencic Associates, and the mastermind behind the scheme, reports MKA has five other speed-core buildings on the boards in three projects in California.