53w53, New York

Rising gracefully to a height of 1,050ft (320m) over Midtown, the building tapers at gently shifting inclines. Randomly spaced diagrids roam freely up the façade, to be reflected in the unique geometry of each of the 139 apartments.

But the diagrid structure is not only an aesthetic flourish. The slenderness of the building means that there is no room for superfluous structure: high-strength concrete and reinforcing steel will be used to construct a shear-wall core, but the façade has to play an important supporting role too.

This presented an interesting challenge for the engineering team, not least because architect Jean Nouvel was also adamant that the building’s complex façade should be a genuine expression of the structure beneath. “Normally we are the ones dictating where the columns go but this was the opposite,” explains Gustavo Oliveira, vice president at WSP New York. “We couldn’t add diagrids in, we had to mimic what was on the façade, so it was an iterative process with the architect. We had never approached a building that way before.”

Concrete Diagrid Structure

The other unusual feature of 53W53’s diagrid structure is what it is made of. Nouvel’s original design was intended to be built in steel. But the floor-to- floor heights of a steel structure would have limited the number of stories too much, so WSP investigated how to create the same aesthetic in concrete instead – “the first time that a diagrid structure of this magnitude and complexity has been done in concrete,” notes Oliveira.

Aside from the complex structural gymnastics, the team also spent considerable time evaluating how 53W53 could actually be delivered. Because of its complexity, construction will take more than five years, around double the program for a more conventional design. One of the biggest challenges was designing the nodes where different structural components would join. Reinforcement for perhaps seven or eight elements had to fit into the same node, and then the concrete had to be able to flow freely to enclose it and produce a sound structure. Oliveira’s team worked closely not only with the architect but the construction team, and this included commissioning a mock-up of the rebar. “Rather than just coming up with solutions that looked good on paper, we assessed the constructability of the job too. Although not typically part of the engineer’s role, this is such a unique building, it needed a unique approach.”