A chain hanging freely takes the one shape in which it is in pure tension; turn that shape upside down and it is the shape of an arch in pure compression for the same loads.
free-hanging chain (catenary) ↔ ideal arch under its own weight
Rules · Cities · Plans · Structure
River, railway and boulevard as one work
Regulate the river, run the city railway beside it, vault the river over and build a great boulevard on the vault, so that engineering and city beauty are planned together.
Wagner’s scheme for the Wien valley would have made a boulevard from the Ring to Schönbrunn over the vaulted river. The regulation of the river and the Stadtbahn’s Wiental line, in a walled cutting on its right bank with Wagner’s stations, were built in the 1890s; the vault was carried only a short way from the centre, and from 1902 the Naschmarkt moved onto it. The rest of the boulevard was abandoned for its cost.
Related rules
Hang a chain (or a model of strings loaded like the building) from two points; the curve it takes, turned upside down, is the ideal shape of an arch carrying the same loads, in pure compression.
A masonry arch stands if a line of thrust (the path of the compressive force through it) can be drawn entirely within its thickness; the catenary arch contains its own line of thrust exactly, the semicircle only if it is thick enough.
catenary: thrust line = centre line · semicircle: needs t ⁄ R ≳ 0.11
A new material calls for new forms: iron should be used in slender members that show its strength in tension and bending, not cast in imitation of stone columns and vaults.
Instead of applying ornament to a structure, shape the structure itself, especially exposed iron, into lines that are both constructive and decorative.
Begin every design from its construction; the architect’s task is to turn the construction into art-form, never to hide it behind forms borrowed from another material.
Cite this page Chris Paton, “River, railway and boulevard as one work”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/wagner-wienzeile. Text, drawings and models licensed under CC BY-NC 4.0.