New Songdo International City Block D24, an Iconic and Efficient Twisted Tall Building Structure

This paper discusses the structural design of a 50 story, twisted residential building structure. It presents an overview of methods employed in the design of the articulated structural shape. It outlines how the project team imposed this articulation without a significant increase in the use of structural materials beyond that typical for rectilinear tall residential apartment buildings. The column-free design consists of structural concrete dividing walls between five apartments on each floor plate, cantilevered in a radial arrangement from a central cylindrical concrete core. The arrangement of the walls is staggered and alternated between floors, and therefore achieves apparent long spans and column-free apartments. The design also allows the floor plates to be rotated sequentially up the height of the building without imposing torsional force on the central core, a common design challenge associated with towers with a twisted form. The paper details the design process, explaining the motives and constraints of the design, and shows how the unusual structural system was derived. The structural engineering design of the system is explained including discussion of load paths and deflection control. The associated structural consideration of seismic performance is briefly discussed. Finally, a comparison of material quantities is made against two other residential tower structures on the same site, which are mostly rectilinear in form. The comparison shows very similar material quantity use per unit floor area between the three designs.