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SOM

The Rocker: Suspending the Limits

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An ingenious solution

The Poly Corporation Headquarters in Beijing features a unique design component created specifically for this building: the Rocker. This elegant system was inspired by an understanding of structures as moving entities rather than static objects.

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An ingenious solution

The Rocker is a daringly engineered device that resolves the complex structural forces of a suspended eight-story museum and one of the world’s largest cable-net curtain walls. Both are defining features of the 22-story-tall open atrium.

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Realizing the cable-net wall

Structural analysis showed that the 22-story-tall cable-net glass wall would not be feasible without additional support. The resulting design concept faceted the glass wall and added two large diagonal cables running along the facet lines from the roof of the museum up to the top of the atrium.

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Realizing the cable-net wall

These cables support the atrium wall while using the suspended museum structure as a counterweight.

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Designing for impact

The team understood that earthquake and wind loads would cause the roof of the building to sway up to 3 feet (0.9 m) relative to the roof of the museum structure over ten stories below. In a conventional suspension system, the two diagonal cables would try to resist this movement, causing the forces in them to increase significantly and their sizes to become untenable.

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Designing for impact

To counteract this resistance, the Rocker acts as a “reverse pulley” that allows the movement of the building roof, museum, and curtain wall to take place freely and safely without significantly increasing the forces in the cables.

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An idea put to the test

The team tested the concept with a working model that was created to simulate the expected relative building movement in an earthquake.

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An idea put to the test

Springs were connected at the ends of the cables. The team hoped that they would not elongate during the side-to-side motion testing, a sign that any earthquake-induced drift would not in fact increase the tension in the cables.

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An idea put to the test

The experiment was a success. It found no significant elongation during the testing, validating the design concept, and the Rocker was installed as the first of its kind.

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Suspending the limits

The Rocker is a testimony to the power of an integrated architectural and engineering approach. In opening up space above and below the museum structure and enhancing natural day lighting and views for the building’s visitors, the Rocker creates a dramatic atrium space with a memorable and dynamic building detail.