The "Steel Dawn": The Challenge of Joining Two Towers in the Void (CCTV Beijing)

Series: Avant-Garde Constructions

Masterpieces of Architecture and Engineering: #02 CCTV Tower, Beijing

Can a colossus with 473,000 m² of floor area float more than 160 meters above the ground without visible supports?

In Beijing, the CCTV Tower headquarters decided to break the sacred rule of the skyscraper: verticality as the only path to success. It is not a tower; it is a continuous three-dimensional ring that folds over itself at impossible angles, creating a 75-meter cantilever that defies gravity.

The Duel of Geniuses: Where "Delirium" Met Logic

The structure of the CCTV was not born from software, but from a unique intellectual symbiosis between two brilliant minds: architect Rem Koolhaas (OMA) and structural engineer Cecil Balmond (Arup).
Koolhaas wanted to end the skyscraper typology as an isolated and predictable "parallelepiped." Balmond, for his part, understood that to achieve this, the building should not be a shape, but a system of interconnected forces. Together, they made the structure the absolute protagonist: it is not a building with a structure; it is the structure made into a building.

We are not designing a form, we are designing a system of forces. — Cecil Balmond.

The Invisible Enemy: Thermal Expansion

The greatest challenge was not just supporting the cantilever, but joining it. The two leaning towers were built separately. Due to Beijing's high solar exposure, the steel of each tower expanded differently depending on the time of day. Attempting to weld them at noon would have been a fatal mistake; the structures would be "out of alignment" by several dozen centimeters.





The Epic Solution: The final connection was made at dawn, the only moment when both towers were in thermal equilibrium and their geometric positions were identical. It was the instant when the two cantilevers touched for the first time, culminating an unprecedented engineering maneuver that closed the circuit of forces in December 2007.

A Challenge of Precision: The operation was so sensitive that, hours before the closure, four key corner columns had to be temporarily removed. This allowed the structure to gain the necessary flexibility to absorb tensions uniformly before being sealed forever. Urban-scale precision surgery that transformed two independent towers into a single symbiotic organism.

The Facade as a "Stress Map" (The Web)

If you look at the building, you will see a network of steel diamonds (diagrid) that is not uniform. This is not an aesthetic whim; it is pure physics.

• High-density zones: Where the diamonds multiply and the diagonals narrow is where the structure undergoes the greatest tension and compression forces (especially at the cantilever nodes).
• Low-density zones: Where the stress is lower, the mesh opens up to allow more light to enter.

The facade is, literally, a full-scale load diagram. The building is "telling" you where the forces travel to reach the ground.

Technical Comparison: Stability through Geometry

As I analyze in my book "TURNING TORSO - SANTIAGO CALATRAVA," engineering approaches iconic milestones in radically different ways:

Turning Torso (190 m): Relies on a rigid cylindrical concrete core and a steel exoskeleton that "holds" the 90° twist.

CCTV Tower Beijing (234 m): Relies on interconnectivity. As a closed ring, the towers support each other. It is a symbiotic structure where the rigidity of the whole compensates for the lack of verticality.

The tower is a bourgeois typology. We have made a building that questions the tower; it is a loop, a circuit, a building that moves. — Rem Koolhaas.

Why doesn't it collapse?

Unlike a conventional skyscraper that works fundamentally in compression, the CCTV functions as a giant rigid frame. The 75-meter cantilever is sustained thanks to the rigidity of the nodes in its external mesh (diagrid) — diagonal brace members, which convert bending into axial forces distributed throughout the ring. It is a challenge to logic that only advanced engineering can solve.

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Frequently Asked Questions:

Is a leaning building safe?
Yes. Through the diagrid system, loads are distributed across the "skin" of the building, making it extremely resistant to earthquakes and lateral winds.

What is a Linked Cantilever?
It is a cantilever that is not "loose" but connects two structures, closing a circuit of forces that provides global stability unattainable for an isolated tower.

Why were the towers joined at dawn?
To prevent thermal expansion caused by the sun from deforming the steel asymmetrically. At dawn, both towers have the same temperature, and their geometry is perfect for assembly.

What does "The Web" mean in this building?
It is not an acronym, but the technical term to describe the steel network (diagrid) that wraps the building. It acts as an active exoskeleton that distributes stress across the facade, making the building function like a living organism.

How does it compare to the Turning Torso?
While the Turning Torso relies on a rigid reinforced concrete core to master the twist thanks to the external spine that runs along the facade, transmitting loads to the foundation, the CCTV Tower in Beijing uses a closed-ring symbiotic structure where both towers support each other, optimizing steel through geometry rather than mass.

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José Miguel Hernández Hernández

International reference in the technical analysis of iconic and sculptural architecture. Specialist in the intersection of engineering, aesthetics, and the avant-garde. Author of the bilingual technical books Turning Torso – Santiago Calatrava and Famous Constructions / Construcciones Famosas.

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