Paper: Capital C, geometric optimization of a free-form steel gridshell towards planar quadrilateral glass units

The former Diamond Exchange building in Amsterdam, now called Capital C, is restored to its former glory and currently undergoing a major renovation. This listed building has been returned to its original design and topped with a spatial gridshell roof structure of glass and steel, designed by renowned architectural office ZJA. This paper focuses on the geometric optimization of the free-form gridshell towards planar quad glass units. 

The final shape of the gridshell is determined by a parametric computer model. With a by ZJA in-house written program, the boundary conditions were defined, where after the software searches the ideal shape. In the case of Capital C, the ideal shape was a geometrical free-form shape but with planar or minimal curved quadrilateral glass. This to represent the faceted aesthetics of the diamond, representing the building’s heritage. In addition to the look, optimizing to planar glass panes also increased the feasibility and cost-efficiency of the design. During this process, Octatube, as a specialist Design and Build contractor, was approached and challenged to realize this innovative and complex design.

In principle, the gridshell has one repetitive structural steel connection. However, due to its shape, every connection is unique and itself composed of many unique parts. In the final design, approximately 1000 different steel elements and 200 different glass units are applied. With a traditional design method, where all elements are modelled one by one, a minor change to the geometric shape of the shell would lead to a large amount of labour. A time-consuming and error-prone job. Therefore the design is automated, by means of an in-house developed parametric tool by Octatube, which converts the complex basic geometry into a FEM-model and detailed production model.

The applied methods of parametric design and engineering allowed the team to not only optimize the glass -design until late in the engineering phase, incorporating a file-to-factory workflow, it also allowed for fast and very precise pre-fabrication. Not unimportant when installing a free-form glass and steel gridshell on top of a listed building in the heart of Amsterdam.

Authors: Jack Bakker (ZJA), Erik Smits (ZJA), Koos Fritzsche (Octatube) and Wouter van der Sluis (Octatube).

This paper was submitted for the 2020 Challenging Glass Conference on Architectural and Structural Applications of Glass.

Read the full paper: Capital C, geometric optimization of a free-form steel gridshell towards planar quadrilateral glass units (pdf).