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Ziggenbach Bridge, Wagitalersee
Ziggenbach, Seestrasse, Wagitälersee, Zurich canton, Switzerland
Ziggenbach Bridge, Wagitalersee
associated engineer
Robert Maillart
Ingenieurbureau Maillart
date  1924
era  Modern  |  category  Bridge  |  reference  Tg292446
photo  Mark Whitby
Ziggenbach Bridge is one of three reinforced concrete bridges designed by Swiss civil engineer Robert Maillart for the road encircling Lake Wägital, south-east of Zurich. The other two, crossing the Flienglibach and Schrähbach, were deck stiffened arches but this one is a hingeless arch, the deck of which follows an unusual polygonal planform. It is still in use.
Lake Wägital (Wägitalersee) is the man-made reservoir impounded behind the Schräh Dam, constructed at Innerthal in 1922-4 for the generation of hydroelectric power. The lake is fed by numerous brooks, including the Ziggenbach, and encircled by a lakeside road, called Seestrasse.
Maillart's two deck-stiffened arch bridges were located at the north end of the lake, near the dam. The Ziggenbach Bridge is on the eastern shore in the southern half. The bridge is sited a little upstream of the lake, where the valley is narrower, reducing the necessary span.
Ziggenbach Bridge was designed by Robert Maillart (1872-1940), an advocate and innovative user of the reinforced concrete. In a typically succinct approach to design, he separated the need for a curved road alignment from the supporting structure, the main element of which is an economical, straight hingeless arch, with oblique approach structures. This was a new concept for Maillart. He would use it again in 1930 on the Landquart River rail bridge at Klosters (demolished by 1993).
The smooth-faced arch is straight in plan and spans 23m, with a rise of 7m. The approaches are carried on full-width piers, which are parallel but their latitudinal positions are determined by the location of the roadway above. The arch springs from these piers, on its own alignment. The deck spans from the piers to masonry-faced abutments on the valley sides.
The plan of the deck approximates a curve using a series of straight sections. Three longitudinal ribs support it on the piers and abutments, following the deck's polygonal alignment. In cross section, the piers are somewhat thicker at the ends and centres. The ribs noticeably increase in depth where they meet the piers, in a way that is reminiscent of the mushroom column heads Maillart invented for beamless slabs in buildings.
Max Bill comments that the bridge is noteworthy for being "free of any kind of architectural detail". Some refurbishment using shotcrete has been carried out, at a date unknown.
Research: ECPK
"Robert Maillart: Builder, Designer, and Artist" by David P. Billington, Cambridge University Press, 1997
"Robert Maillart's bridges: the art of engineering" by David P. Billington, University Press, Princeton, New Jersey, 1979
"Robert Maillart: Bridges and Constructions" by Max Bill, translated by W.P.M.K. Clay, Pall Mall Press, 3rd revised edition, November 1969

Ziggenbach Bridge, Wagitalersee