Lately, an 86. 6-metre-tall mass-timber（拼接木材） tower in Milwaukee, Wisconsin designed by Korb+Associates Architects, has been certified as the world's tallest timber building. Located in a neighbourhood near the lakefront, the 25-store y tower is made almost entirely from timber except for the base, elevators and stair shafts（竖井）.
The structure took only two years to build. It has a concrete-framed podium（基座） at the base that is six storeys tall and the 19-store y timber tower rises from the podium. The core containing the elevator shaft and staircase is made of concrete to help the building deal with wind and earthquakes, as well as for fire safety reasons. "Our cores are concrete, "Korb+Associates Architects founder Jason Korb said.
Thornton Tomasetti associate Alejandro Fernandez, who worked on the project, said that the city required a three-hour fire rating for the columns, so the team worked with the Forest Products Laboratory to optimize the columns to meet this standard. "We think it was the first three-hour fire testing on columns, " said Fernandez, adding that the floor plates had a two-hour rating, meaning the components can burn for two hours without losing structural integrity.
Because of requirements preventing external wood exposure and the developer's desire to capture the lake views, the outside of the structure is made almost entirely of glass and metal panelling.
Both Korb and Fernandez agreed that many of the drivers behind the project were economic——from the real estate perspective of the facade（建筑物正面） to the cost restrictions of the timber. Much of the wood was sourced from Austria because sourcing high-quality supplies from North American manufacturers would have been too expensive. Economic benefits were increased by labour usage of the project. Korb estimated that the project used about 25 per cent of the onsite labour required for a concrete structure and that it was completed in about half the time.
Both Fernandez and Korb believe that the tower will provide further proof of concept for developers who are looking to create innovative structures from timber. And mid-rise developments like these that "attract people to the urban core"are a "good"thing, Korb added.
