Korean building by UNStudio, Architects

The two towers are proposed in reinforced concrete with outriggers. This proposal is an economic, sound and fitting structural solution for a tower of this use, size and proportion. Within this structural system the core carries lateral shear loads and the outriggers mobilise the columns to carry vertical bending forces, limiting lateral movements and accelerations at the top of the building. The lower floors of the tower are all of standard floor dimension and repetitive floor to floor to allow the use of flying formwork.

The formal transition zone in which the cruciform (4 plan extensions) plan configuration adjusts to a triform (3 plan extensions) occurs within a defined centre portion of the building. Within this zone are two sets of outriggers at the top and bottom of the transfer structure. The transfer structure is formed by a triangulated cylindrical warren truss making the transfer between the six upper columns and the eight lower columns. Outriggers are required at the top and bottom of these transfer columns. The outriggers are storey deep trusses between the core and outer columns. The outriggers mobilise the columns in tension and compression to limit the lateral deflections and more importantly the accelerations at the top of the building as described above. Outriggers are required at the top of the building as well.

There are several inclined columns in the transfer zone. There are 12 columns making the transition from 8 to 6. That is each of the 6 upper columns splits into 2 creating 12. These then rejoin such that 4 of the lower columns receive 2 raked transfer columns from above and are tied laterally by the inclined geometry of the raking columns. The remaining 4 lower columns receive only one raking column and there is a resultant thrust. This however is tied laterally to the adjacent column in the pair and resolved back into the curved warren truss system.

Source: m i l i m e t d e s i g n