Tuesday, November 22, 2016

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




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