Form Finding Flashback: Basento Viaduct

It is unclear where the unusual shape of the Basento Viaduct (Potenza, Italy) was derived.  Some even say the thin shell concrete pedestrian bridge is shaped like the headdresses of nuns in Federico Fellini’s Italian films [1].  Regardless, the Basento Viaduct is an example of a structure designed using early form finding techniques.

side by side
Similarity in shape between the Basento Viaduct (left) and nun’s headdress (right)      [Photo Credit [1], [2]]
Today, we rely heavily on the use of computational methods for the form finding of thin shell structures. Yet, we see existing shell structures around the world that were designed and realized before engineers had numerical technology.  Who were these extraordinary engineers and how did they generate these unique forms?

musmeci
Sergio Musmeci (left) in front of just completed Basento Viaduct [Photo Credit: Paulo Musmeci]
One of these form finding pioneers was Sergio Musmeci [1926-1981], a talented Italian engineer and architect.  Musmeci was able to create awe-inspiring bridges like the Basento Viaduct in Potenza, Italy [1969], before computer generated models were commonplace.  While striving for structural elegance, he also achieved structural and material efficiency in his bridges through the use of physical models, analytical formulations and simple finite-difference simulations.  Musmeci relied on physical form finding techniques, like soap films (equi-stressed minimal surfaces) and pre-stressed neoprene membranes (membrane surfaces with different stresses in the main directions), to generate force-modelled, three-dimensional forms for the bridge.   Throughout the development of the form of the bridge, Musmeci refined the physical form using Laplace equations and finite difference methods.  He verified its structural feasibility using physical methacrylate and concrete models as well as a one dimensional beam model (his steps are outlined in the table below).

form finding steps
Diagram illustrating the stages in the design process of the Basento Viaduct
side by side2
Musmeci’s physical soap film model (left) and Neoprene model (right)                          [Photo Credit: Capanna [3], Musmeci [11] of full paper]

Together with Stefano Gabriele, Paola Magrone and  Valerio Varano from Roma Tre University,  we were able to make a computer generated model of (a section of) Musmeci’s Basento Viaduct through a well-established form finding technique known as Dynamic Relaxation.  By restraining nodes at boundary conditions as well as on symmetry boundaries and employing kinetic damping, we were able to create a model very similar to the existing concrete shell structure.  When comparing the actual shell with computer generated models, we can see that Musmeci’s bridge began to stray from a minimal surface geometry he initially aspired to.  By revisiting historical structures and past techniques, like those of Musmeci and the Basento Viaduct, we can compare and influence the design of future thin shell structures.

bridge model
Computer generated model of Basento Viaduct (Principal stresses shown under self-weight of deck and shell loading)

Our paper is now available HERE for more information.

Author: Kendall Schmidt,

 

 

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