GAD Editorial · Published · · English study · Chinese summary · Study dated 2026-10-08
A diagonal on a tower facade can be a brace, part of a larger load-bearing tube, or one element in a system dominated by a central core. Its appearance alone does not reveal what it supports. CCTV Headquarters in Beijing, HSBC’s Main Building in Hong Kong and Turning Torso in Malmö make a useful comparison because each puts substantial structure on display, yet each assigns a different job to that visible framework.
The distinction matters at the scale of a room. Where structure gathers loads determines which parts of a floor can remain open, where a transfer is necessary and how the occupied edge meets the glass. Calling all three buildings “exoskeletons” would flatten these relationships into a style.
CCTV: the perimeter closes a loop
Completed in 2012, OMA’s CCTV Headquarters joins two leaning towers through connections at the bottom and high above the ground. OMA describes an architectural loop; structural engineer Arup explains how the exterior forms a continuous braced tube. The facade’s diagonal pattern varies in density according to the forces the system must accommodate. It is therefore an expression of a changing structural demand rather than a uniform decorative mesh. OMA project record; Arup engineering account.
The high-level connection is crucial to reading the building. These are not simply two independent towers with a corridor placed between them. Closing the loop changes the behaviour of the whole assembly. Arup’s account of monitoring the towers before joining them also shows that the completed structural diagram was reached through a carefully controlled construction sequence. A drawing of the final outline omits that temporary condition.
HSBC: floors belong to suspended groups
Foster Associates’ Hong Kong headquarters, developed with Arup, was occupied in 1985 and formally inaugurated in 1986. Here the conspicuous steelwork organises a suspension structure. Eight masts and substantial trusses collect the building’s loads, while services are placed toward the edges. HSBC’s own history relates this arrangement to the bank’s requirement for changeable office space. HSBC historical record.
The architectural consequence is legible vertically. Groups of floors belong to larger structural intervals instead of repeating one indistinguishable storey after another. At the base, the building rises above a sheltered plaza, with escalators entering the banking hall through its underside. The structure shapes both the office section and the encounter with the street. This differs from CCTV’s continuous perimeter: the key reading is the relationship between mast, suspension truss and the floors associated with it.
Turning Torso: the spine works with a core
Santiago Calatrava’s Turning Torso, completed in Malmö in 2005, arranges nine principal units around a reinforced-concrete core. The external steel spine is connected to those units with diagonal and horizontal members. Calatrava’s project description identifies the core as the main load-bearing structure and explains the spine’s contribution to strengthening and stiffening the system. Architect’s structural account; HSB project facts.
The visible steel should therefore be read together with the comparatively hidden concrete. A photograph can exaggerate the apparent independence of the spine because it stands apart from the facade. In section and plan, the relationship is more reciprocal: the rotated residential floors, central support and external members constitute one coordinated arrangement.
The comparison changes what deserves attention in a tower drawing. CCTV asks how a perimeter becomes continuous through a change of direction. HSBC asks how a floor connects to a larger suspended group. Turning Torso asks how an external frame cooperates with a central core. These are different architectural propositions, not competing claims to structural honesty. Reading them well means following the load path beyond the most memorable outline, then returning to the spaces that path makes possible.