Prefabrication experiments - 114 - Structures - 5 - Folded Plate Structures

Normally related to but not exclusive to reinforced concrete thin shell construction, the folded or pleated plate structure is essentially a three dimensional geometric assembly of planar elements through rigid edges. The creased surface's stress lines induce a complex transfer of loads across the surface portions and linear folds of the pattern. Folds increase the material distance from the configuration’s rotational centre, which increases the systems’ capacity to resist angular stresses. While an area can be pulled in one direction buy a load other interrelated surfaces push or pull in opposing directions. Originating in paper folding principles, multi-directional folds act as stiffeners.

Divided into surface or truss systems, both strategies create thin surface polygonal envelopes that behave similarly to arches or vaults. Much like the voussoir segments of an arch, loads are transferred through stress line vectors. As the folds are increased in height or depth overall spanning capacity is increased as each surface mimics a vertical beam. Tighter and greater geometric subdivision also increases capacity as the stress and bending moment of each ridge is reduced. The resulting architectural space can be planar or follow curved patterns.  

Skidmore, Owings & Merrill (SOM)'s folded surface and truss triangular arch at the US Airforce Academy Chapel at Elpas Colorado or Herbert Yates’ Plydome folded cardboard agriculture workers’ shelters typified architectural and engineering fascination with the pleated structures throughout the 20th century. The folded plate although not exclusive to modernity became synonymous with innovative structures and materials.

Building on the explorations in engineered timber and the folded plate as a structural and geometrical archetype, the iBOIS laboratory at EPFL (École polytechnique fédérale de Lausanne) is examining and experimenting folded plates’ contemporary potentials. Banking on timbers’ relatively low embodied energy and weight, plywood surfaces reproduce geometrical patterns of paper folding while being inflexibly joined together.   The Chapel St-Loup a collaborative effort between Localarchitecture and the iBois laboratory demonstrates the simple manufacturing principle of fixing numerically cut pieces determined from fold patterns. The joinery is a mix of traditional lap and dovetail to achieve a rigid edge joint. The exciting research proposed by this university lab showcases structural capacity, dynamic space creating qualities and the formal geometric elements of folded architecture.

Chapel St-Loup (construction) and iBois laboratory experiment

Prefabrication experiments - 113 - Structures - 4 - Volumetric or box type construction

Also described as volumetric construction, a box structure is basically a rectangular prism component for building. Volumes/modules are either self-supporting or designed to sit in or to be supported by a separate collective infrastructure. The rectangular prisms are usually defined according to standard regulated shipping dimensions and can be completed to varying levels in a factory. The combination of manufactured boxes informs building erection with a potential «toy building block» variability.

The particular advantage of volumetric systems is that much of the construction process takes place within a quality-controlled environment. The factory setting is accommodating and a streamlined organization of procurement, design and production is possible. Transportation costs and important investment in factory production comprise some of the drawbacks of off-site volumetric construction.

Boxes can be cast in concrete or assembled in wood or steel frames. Iconic 20th century box systems employed reinforced concrete or prestressed concrete. Concrete volumetric construction matured during Operation Breakthrough in the U.S. as the postwar building booms in industrialized nations underwrote the development of various concrete box systems designed and engineered according to their vertical and horizontal aggregation. The Habitat 67 prototype designed by Moshe Safdie in Montréal is one of the flagship examples of concrete box building. Reinforced concrete boxes were amassed in a dynamic form, which produced a canonical 20th century architectural marvel. The boxes were fabricated on site as an assembly line was established adjacent to the building site. Manufactured fibreglass kitchens and bathroom were fitted in the boxes.

Once assembled, volumetric construction is permanent, which renders future changes and adaptability difficult. This challenge has constantly argued for some type of hybrid system. For instance, the assembly of bearing service volumes over open frame structures would allow for some flexibility. Grouping has also been explored as a potential to achieve greater flexibility of volumetric building systems. The Shelley System patented in 1970 explored a checkerboard pattern of boxes in order to avoid double walls of adjacent boxes. Furthermore the pattern structured a series of voids accommodating adaptable spaces. The brick like pattern created a permeable structure. The staggered units were attached and post-tensioned by cables running through superimposed faces and ridges.

Shelley system patent drawing