The very knobby pineapple

Walking through design offices and flipping through archives, we’re often struck by glimpses of images that aren’t immediately decipherable — the one above, for instance. Our What’s That? series tells their stories. 


In the 1960s and ’70s, high-rise construction transformed city skylines throughout the United Kingdom. Many of the new structures were designed by architect Richard Seifert, whose best-known creation, the National Westminster Tower (now called Tower 42), remained the tallest building in London for more than 30 years.

The cover story of December 1969’s Arup Journal discusses the firm’s work on Seifert’s NLA Tower, located in a London commuter suburb. Asked to create a visually distinctive 23-story office tower, Seifert developed a unique plan that involved rotating alternate square floor plates by 45 degrees, then lopping off the corners to create octagons.

Croydon Tower floorplan Arup

Typical floor plan

The resulting structure looked “rather like a very knobby pineapple,” according to engineers Tom Henry and Peter Ryalls, who authored the Journal article. (Similarly colorful asides are scattered throughout the otherwise highly technical piece; poorly mixed concrete “looks like it has been visited by a large number of rabbits.”) The image at the top of the page shows a detail of a scale model of the tower.

No. 1 Croydon tower

The building in 2015 — originally called the NLA Tower (or, colloquially, the threepenny bit building), it’s now known as No. 1 Croydon.

In the article, Henry and Ryalls discuss the engineering challenges encountered during the project’s design and construction. One of the most significant involved eight sloping columns of varying lengths at the building’s base.

Column elevations and sections

After abandoning the initial plan of constructing the columns from reinforced concrete, Arup worked closely with fabricators and contractors to devise a steel solution.

Read the full article here.

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