Structural Engineering Award of Excellence: Manhattan Loft Gardens, London

Zhaofan Li
Structural Engineering Associate Director
Skidmore, Owings & Merrill LLP, Shanghai

An Asymmetrical Notching Strategy Yields Robust Structural Solutions

The structure of Manhattan Loft Gardens is perhaps most distinguished by two triple-height sky gardens that take the form of notches cutting completely through the building at levels 7 through 10, and again at levels 25 through 28. Each notch eliminates half of the perimeter columns, and is made possible by a unique steel and post-tensioned concrete hybrid transfer structure, incorporated into the floors above the notches. The steel belt trusses are light and visually permeable, to allow substantially unobstructed views out of apartment windows located within the transfer structure. The post-tensioned concrete outriggers occur between apartment layouts, where visual permeability is not required, and the resulting post-tensioned structure is substantially stiffer than an equivalent steel truss would have been.

Overall stability of the tower is provided primarily by the central reinforced-core wall, with additional stiffness resulting from the interaction between the post-tensioned outriggers, belt trusses and the perimeter columns. Above each notch level, a one-story-deep steel perimeter belt truss carries the gravity load of the columns for 15 stories above (up to the next notch level or roof). The belt trusses, in turn, are carried by four post-tensioned concrete outriggers that emanate from the central core.

View Building on The Skyscraper Center