Column_6: Swelling and Shearing (part 6 out of 9 from New Orders)
Entasis is the application of making a column conical (rather than just cylindrical) to rectify the visual perception of concavity produced by a straight shaft. This technique is assumed here less for visual correction but rather to initiate a structural query. By swelling the central shaft of the column, six vertical sections demark an array of independent shear walls, some at the extremity, left free from the ground. The research begins with how to interconnect the walls into a cohesive structure while concurrently formulating an integrated organization of varied living spaces.
The vertical transposition of Frei Otto’s high and low points tensile membranes, brings the potential for a field of connecting points between the different shear walls. A constellation of positive and negative normals to the original planes of the walls distorts them to form bulges that bind the walls together. This set of protuberances not only provides greater lateral resistance to the wall structure but also directs the principal organization of the living units for the project. Each unit is laid out following two main directions in space, one frontal, receptive to light, and the other transversal to increase natural ventilation across the connecting walls.
The prototyping exercise for the making of the walls exploits the simplicity of Frei Otto’s original geometry, economically described by a set of high and low points. The three-dimensional surface derived from this set of points is efficiently achieved by interpolating a sheet of textile onto a constellation of physical vectors, bounded by edge profiles. The fabric is secured on the wooden vectors with plugin elements that later provides the connections between the cast walls. The fabric is then hardened with epoxy to finalize one of the two parts required for the formwork. The second part of the mould is a direct copy of the first. It is fabricated by applying a thin layer of rubber onto the first part, backed with a plaster cast support. Three complete formworks are reused twice for the concreting of 6 walls, later mechanically connected as a whole.
Overall, the method employed for the prototype is a much refined and more efficient version from the one executed for column 2. The high surface definition of the concrete walls (double-curvature) generates a high degree of surface suction on the formwork. A rigid mould would have subjected the concrete shells to large stresses during decentering and as a result they most likely would have cracked. However, the thin and ductile layer of rubber, introduced in the sandwich of the formwork, greatly contributed to the ease of the demoulding process.