Since industrialization reformed engineering and its education, normalized structural frameworks’ materials, sizing and detailing have orchestrated building construction. In post and beam braced frames, mathematical calculations and catalogued precedents became the way forward to inform component specification. For all load-bearing elements, engineers evaluate and size according to constraints to shape a stable structure with manufactured parts: beams, struts, posts. Before industrialized frames, in masonry construction, geometry, namely arch effect was deployed more intuitively in domes, arches, and vaults to resist vertical loading in a shape inversely proportional to gravitational loads. Catenary arches and funicular figures represent idealized lines of stress that minimize tension, important for masonry structures. Modern engineering principles and longstanding arch effect have also been combined to optimize the link between structural form and a material’s tendencies. Freyssinet's prestressed concrete using tended cables to compress concrete is perhaps the greatest expression of harmonized tension and compression in structures to produce a superlative material.
Another structural genius, Robert le Ricolais, professor at Penn State in the 1950s explored potential lightweight spatial structures, their geometry and the interplay of compression and tension to propose some of the most unique structural spanning elements of the 20th century. His Polyten Bridge developed in 1968-69 while still at Penn is a notable example of using the prestressing principle that is normally applied to concrete to compose a resistant geometry. The unit leverages, the bowstring truss principle to tie and arch a superior cord. Symmetrical king posts expand the shape at its center to resist the greatest loads. Together, top cord and bottom cables connected by a web of interrelated struts (short columns suspended within the framework) create a thick wing-type space frame. Akin to tensegrity (compression suspended in tension) the frame could be used for roofs reducing the amount of material that would normally be used by a monolithic element to cross the same distance. The Polyten bridge's geometry and structural effect accord compression and tension to arrange a robust structural framework that literally hangs arched and linear struts within a web of stretched cables in the service of an idealized structural efficiency.
Polyten Bridge - Robert le Ricolais
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