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Schrahbach Bridge, Wagitalersee
Seestrasse, Wagitalersee, Schwyz canton, Switzerland
Schrahbach Bridge, Wagitalersee
associated engineer
Robert Maillart
Ingenieurbureau Maillart
date  1924
era  Modern  |  category  Bridge  |  reference  Tg266472
photo  Jane Joyce
Schrähbach Bridge is the second of Robert Maillart’s deck stiffened arches. It is one of three bridges he designed at Lake Wägital (Wägitalersee) — two deck stiffened arches and one hingeless arch. Though modified, the bridge crossing the Schrähbach watercourse is still in use, carrying the shoreline road that encircles the lake. However, its demolition has been approved and it may not stand beyond 2014.
Schrähbach Bridge is about 250m west of the Schräh Dam, which retains the man-made reservoir of Lake Wägital. It was designed by Swiss reinforced concrete entrepreneur Robert Maillart (1872-1940) in 1924, the year after his first deck stiffened arch bridge was completed, over the Flienglibach on the opposite side of the lake (now demolished).
The bridge is 41m long overall and 3.6m wide, and has a single span of 28.8m, making it a little smaller than the Flienglibach Bridge. Maillart’s design allowed the deck and the arch to work together as a unit, with each carrying a proportion of the load and giving strength to the other. The advantage of this approach is that it minimises differential movement cracking, and — of equal value to Maillart — the arch can be slimmer as it doesn't carry all the stresses.
At Schrähbach, the arch is even thinner than that of the earlier bridge — just 180mm thick at the crown and 220mm adjacent to the abutments. The deck is almost horizontal (slightly higher in the centre) and supported by four thin vertical transverse walls on either side of the crown. Deck stiffness is provided by 1.1m deep structural parapet walls on the 240mm-thick deck.
Soon after completion, the bridge began to show signs of frost damage, which also affected the Flienglibach Bridge. The concrete used for both included constituents that were not frost-resistant.
In 1933, the frost damage on the Schrähbach Bridge was repaired with a layer of sprayed concrete. Longitudinal rendered brick walls were added to both sides of the bridge, closing the openings between deck and arch, and giving the structure a much heavier appearance than its designer had envisaged.
The Swiss Federal Material Research Station carried out a programme of testing on both bridges, which was evaluated by Professor Mirko Ros (1879-1962). In 1937, he reported that the results of stress recording and load testing had proved very satisfactory. Maillart’s innovative design was vindicated.
However, since that time the condition of the Schrähbach Bridge has deteriorated. It's not included the cantonal inventory of buildings to be protected and in 2009 a local referendum voted for its replacement. An appeal was quashed in 2010, despite objections from Swiss heritage and cantonal historic preservation organisations, Bund Schweizer Architekten (Federation of Swiss Architects), Schweizerischer Ingenieur- und Architektenverein (Swiss Society of Engineers and Architects), the engineer Christian Menn (b.1927) and the architectural historian Werner Oechslin (b.1944).
In December 2013, demolition of the Schrähbach Bridge was authorised and may take place in 2014. The replacement is intended to look similar to Maillart’s original but will have its load capacity increased from 12 to 40 tonnes.
Contractor: Prader & Cie, Zürich
Contractor: F. Favetto, Brunnen
Research: ECPK
bibliography
"State-of-the-art of spatial arch bridges" by Marta Samiento-Comesías, Ana M. Ruiz-Teran and Ángel C. Aparicio, in Bridge Engineering, ICE Proceedings, London, May 2012
"Robert Maillart: Builder, Designer, and Artist" by David P. Billington, Cambridge University Press, 1997
"Robert Maillart and the art of reinforced concrete" by David P. Billington, Architectural History Foundation, MIT Press, 1990
"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
http://news-world-architects.com
www.frei04-publizistik.de
www.schwyzkultur.ch
Location

Schrahbach Bridge, Wagitalersee