Sited between God and Mammon, between Birmingham’s new temple to consumerism, the Bullring Shopping Centre, and the newly renovated St Martin’s Church, lies the small but perfectly formed, shell-like structure that is the Spiral Café. The client Birmingham Alliance’s brief had called for the creation of a landmark structure that would animate and enliven the terraced St Martin’s Square in which it sits, but one that would also generate an income. It needed to be rugged and suitable for use in all weathers, yet have a high degree of transparency.
Our competition-winning design, only 60 square metres in size, is large enough to allow shoppers to sit inside comfortably and enjoy the view, but small enough to be viewed as a piece of sculpture in its own right. Wanting a building that would stand independently of its surroundings, we took our inspiration from the Fibonacci sequence, a simple mathematical formula first identified by Leonardo Fibonacci in the thirteenth century. Starting by adding one plus one, each subsequent number is calculated by adding together the two previous numbers in the sequence, creating an infinite run that begins 1 1 2 3 5 8 13. Related to the Golden Section, the sequence has been found to have an almost mystical relationship with natural patterns of growth, from the shapes of sea-shells and pine cones to the geometry of complex fractals in galaxies. Read more
Illustrated graphically, the sequence generates a graceful spiral, and the Café’s form was derived by sweeping this ‘golden spiral’ along a tilting axis to create a simple enclosure formed around just eight curved structural ribs. Promoting the building’s shell-like form, the outide is clad with roughly encrusted post-patinated copper sheets and inside with smooth bronze plates finished with a clear lacquer. Spherical lights, hanging like pearls over the bar inside, complete the analogy.
The ribs were fabricated from mild-steel plate cut on a computer-controlled plasma cutting machine and follow a near-identical geometry, with only the ‘inner’ end of the spiral adjusted to create a more suitable shape where the ribs rise inside the building and enclose the bar. This meant that the form of the building could be manufactured easily, with only a series of simple steel tubes set diagonally between the ribs required to hold the cantilevered structure in place.
A product design programme was employed to develop a parametric three-dimensional model of the building, which was used to outline and then refine all the architectural and structural elements in a continuous process that allowed the engineers and ourselves to work on the model at the same time. The working drawings were then generated directly from the completed model, setting accurate profiles for the fabricator who could add any additional information, such as bolt holes and splice locations, before cutting began. Unsurprisingly, this resulted in a very high degree of accuracy, which only added to the jewel-like quality of the completed building.