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Prototower 03

DRX 2013

Bundled Tube Systems

Sean Buttigieg, B.Arch., Dragos Naicu, M.Phil. 

Bundled Tube Tower

The aim was to develop a vertical net structure based on the concept of bundling, inspired both by natural systems such as plant cells, as well as architectural precedents such as the Willis Tower in Chicago. Bundling can be interpreted as a multidimensional framework that would allow the design of a vertical net as a function of programmatic, structural and infrastructural parameters.

The generative process that was developed to explore this avenue involved digital modelling using spring-based physics, geometric manipulations in 2D and 3D as well as performance analysis and feedback. The Prototower that evolved from this framework features an overall integration of programmatic and structural qualities by using a perimeter frame system in combination with a decentralised core. Furthermore, its spatial qualities are augmented by a varying overall silhouette and by the introduction of large atria within the tower.

Generative Process

The starting point of the exploration was the definition of a spring-based model featuring five vertical fibres that define the base and tip as well as a number of intermediary cut-off levels. These fibres, representing individual tubes, are made up of 100 springs each and are interlinked by another set of (invisible) springs at levels corresponding to the floor slab layout of the tower. For a 450m tower with 100 floors this would happen every 4.5 m thus providing a relative amount of control over individual levels.

This setup had a number of parameters that allowed the creation of a phenotype of potential towers:

• Fibre stiffness

• Fibre rest length

• Interlink springs stiffness

• Interlink springs rest length

• Interlink springs proximity control

The exploration of the range of possibilities offered by these parameter sets led to a design that is most responsive to the types of criteria that would normally be imposed on a tower (e.g. overall aesthetic, structural concept, program distribution, etc.).

The tower form is achieved by using Voronoi cell packing at each individual level across the height using as starting points the fibres that have now been deformed. This creates a smooth perimeter zone made up of 5 circular arcs and an interior structure based on the Voronoi lines. The tower features 5 tubes, with 3 of them cutting off at a various levels below 450m. These zones are where three spacious atria are created.

Tower Hierarchy

The next step in the generative process involved the development of a structural hierarchy based on the geometry output from the fibre bundling algorithm. Using the information embedded in the Voronoi packing, as well as other criteria, the structural system, or vertical net of the tower, was extracted. The main components of this are:

• 5 Megacolumns (at the perimeter cell intersections)

• Perimeter columns and beams

• 5 Cores (based on the interior cell intersections)

• Core-to-core bracing

• Core-to-megacolumn link

One of the real advantages of the bundling framework is that the geometric information that results can be extended to a number of detail levels. For example, in addition to perimeter columns and beams, façade mullions can also be generated. 

Structural Analysis

The structure was designed and optimised for displacement at the top and minimum steel tonnage. It was shown that lateral stability, one of the main design drivers for high-rises, could be achieved by the perimeter frame while maintaining a competitive value of steel tonnage per floor area.

In addition, by introducing the internal structure and linking it to the perimeter, the lateral loads can also be shared by the 5 cores, potentially leading to smaller structural elements throughout. Furthermore, this introduces vertical elements within the tower that allow the possibility of spanning floor slabs over feasible distances with minimal intrusion into the usable space.

The structural analysis was performed using Karamba 3D static analysis and its built-in cross-section optimisation tool that allows the definition of larger sized members where needed, while maintaining within the displacement and tonnage tolerances.

The nature of the generative framework, which features a hierarchical output, provides the added opportunity to design for specific requirements by optimising member sizes for each level of hierarchy. For example, maximising floor-to-ceiling heights is often desirable. This can be achieved by specifying a maximum height for the perimeter beams and optimising the other structural elements in order to maintain overall performance levels.

Program

The program of the Bundled Tube Tower is derived together with the structural system and offers a substantial total floor area. As is typical for a tower of this size, there are five main zones of program, going from base to tip: Retail, Office, Hotel (including luxury suites), Residential and Entertainment. In addition, Lobby zones are defined according to the three atria and become transitions from one zone to another. While offering generous space and outward views, they clearly express the space-making potential of the proposed generative framework.

One of the ways in which the structural and programmatic requirements meet is through the fact that it is possible to provide uninterrupted floor plates between main structural components. This openness is augmented by another direct output of the generative process, which is a natural variation between floors that offers the freedom to interpret the potential of the spaces in an immensely creative way.

Conclusions

The Bundled Tube Tower is a showcase for what the wider concept of bundling can achieve. By integrating the vertical and horizontal development of the system, a holistic framework was created which delivers both architectural and structural qualities. In addition, one of its main advantages is the adaptability of the generative process to site conditions and a large number of criteria. Finally, all these benefits arise from a framework that also creates the possibility to develop a wide palette of forms and spaces.