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Valtschielbach Bridge
Valtschielbach, Donat, near Zillis-Reischen, Graubünden, Switzerland
Valtschielbach Bridge
associated engineer
Robert Maillart
Ingenieurbureau Maillart
date  1925
era  Modern  |  category  Bridge  |  reference  Tg742002
photo  Adrian Michael (own work), CC-BY-SA-3.0-2.5-2.0-1.0 via Wikimedia Commons
Sometimes referred to as the Donat (or Donath) Bridge, Robert Maillart's reinforced concrete road bridge across the Valtschielbach in the hamlet of Donat is the earliest of his deck-stiffened arch schemes surviving in its original form. Now bypassed by an adjacent new bridge, the structure is open for foot traffic and has recently been extensively refurbished.
The bridge, over a deep ravine of the Valtschielbach (Valtschiel brook), was designed by Swiss pioneer of reinforced concrete, Robert Maillart (1872-1940). He used a much simpler approach to designing deck stiffened arch bridges than was common at the time, when exhaustive theoretical calculations were expected. His concept expressed a far more holistic view of structures.
The design of this bridge was encapsulated in just three and a half pages of hypotheses. Its form is a development of an earlier pair of deck stiffened arches he designed for streams at Lake Wägital (Wägitalersee), south of Zurich, though it has a much longer span.
Based on observing the in-service behaviour of his bridges, Maillart realised that the deck and the arch, when working together, carry bending moments proportional to their flexural stiffness. In this design, the deck is restrained by parapet walls and so is significantly stiffer than the arch. Consequently, the deck can carry practically all the bending moments, producing a structure that is more than eight times as efficient as a simply-supported beam.
The shallow arch of the Valtschielbach Bridge (Valtschielbachbrücke) rises 5.2m and spans 43.2m. It was cast in situ on timber centring carried on fan-shaped arrangements of timber supports anchored to the ravine’s sides. Once the arch was cast, it acted as the support for construction of the superstructure.
The arch is only 230mm deep at midspan, and 290mm at the abutments. Over the central portion of the span, measuring 11.6m long, the arch is fused to the underside of the deck. Where the two diverge, they are braced on each side by four vertical transverse walls, 160mm thick, and at 3.1m centres.
The deck structure is a maximum of 1.2m deep overall, with a parapet depth of 1.1m. Each parapet is a solid wall, pierced at roadway level by 14 drainage openings. A projecting lip, 200mm deep and 100mm wide, runs along the top of each parapet, optically correcting the heaviness of the parapets' appearance.
The bridge is straight in plan, with sharp transitions in the roadway on either side, leading to two substantial masonry abutments some 6.1m long, each with a central 2.5m wide vaulted arch. The bridge carries a single-track roadway, 3m wide, and is 3.6m wide overall.
Construction was completed during 1925, at a cost of 40,000 Swiss Francs. In accordance with Swiss practice, its structural integrity was verified by load testing, in September 1926. The allowable loading was 7 tonnes per vehicle, or 300kg per sq m.
Since 22nd August 1995, the bridge has been owned by the Gemeinde Donat (municipality of Donat), who provided heritage protection by giving it a Grade II listing. Around the same time, a new wider bridge carrying the Surses road over the Valtschielbach opened adjacent and east of it. Maillart's bridge is now only for pedestrian and cycle use.
In October 2009, an inspection of the bridge showed numerous rust spots and chipped concrete, all resulting from frost action. Most damage had been caused by water draining through the roadway apertures. Road salt had not been used on the bridge, so it was anticipated that any corrosion of the reinforcement would be superficial.
In March 2013, a 760,000 Swiss Francs restoration contract began, under the supervision of consultant Conzett Bronzini Gartmann AG from Chur. The work ensured that the bridge’s appearance was maintained and intervention minimised. It included the replacement of damaged areas of concrete in the deck and arch using shotcrete and gunite techniques. Reprofiling the roadway has been done to improve drainage and keep water away from the openings in the parapet walls.
Contractor: Nicolaus Hartmann & Cie of St Moritz
Research: ECPK
bibliography
"Conceptual Transparency: Examples from the Work of Robert Maillart and Jörg Schlaich" by E.M. Hines, Tufts University, Medford/Somerville, Massachusetts, 2011
"Robert Maillarts Valtschielbrücke in Donat Sanierung eines Kulturdenkmals", Gemeinde Donat, Wergenstein, October 2011 [in German]
"The Revolutionary Bridges of Robert Maillart" by David P. Billington, in Scientific American, pp.84-91, July 2000
"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
www.donat.ch
www.suedostschweiz.ch
www.swiss-timber-bridges.ch
Location

Valtschielbach Bridge