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Engstligen Bridge (Spitalbrucke), below Adelboden
Engstligen River, Landstrasse, Spittelbrugg, below Adelboden, Berne canton, Switzerland
Engstligen Bridge (Spitalbrucke), below Adelboden
associated engineer
Robert Maillart
Ingenieurbureau Maillart
date  1931
era  Modern  |  category  Bridge  |  reference  Tk348672
photo  Jane Joyce
Maillart’s 1931 deck-stiffened concrete-arch road bridge over the Engstligen River in western Switzerland, north of Adelboden, was his first skew crossing. The solution he devised uses two identical arches set side by side but not parallel. The bridge is still in everyday use, though quite hard to spot from the winding mountain road.
The Engstligen road bridge is also known as the Spitalbrücke (Hospital Bridge). Its creator, Swiss engineer Robert Maillart (1872-1940), was an inventive structural designer and early champion of reinforced concrete. The bridge was built alongside a earlier roofed timber bridge, which it was designed to replace. The old bridge was later dismantled and re-erected in Margeli, Adelboden.
Maillart’s bridge is 45m long and 7m wide, carrying a 5.8m two-lane roadway at a shallow gradient of about 1 in 45. It crosses the river at angle of approximately 56 degrees and the required span is 30m bank-to-bank. However, a single arch span at this point would have to be larger to accommodate the alignment of the river.
Instead, Maillart devised a cost-effective scheme that is also visually pleasing — an ideal combination to his mind. He used two identical arches, making construction simpler, and cheaper, not least because it required half the formwork and scaffolding, erected twice.
The bridge was cast in situ. Each shallow arch is 2.45m wide, and they are set 2m apart, offset horizontally in the direction of road travel by some 2.75m. The arches rise 3.3m from their spring points to the underside at the crowns. Each slab is 240mm deep at midspan and 260mm deep at the ends.
The deck of the bridge is one slab supported on (and stiffening) both arches. A series of thin concrete cross walls connect deck to arches. These could have been two independent identical sets, one for each arch, which would have meant not aligning them across the bridge width. However, Maillart made them continuous and they consequently cant at varying angles to accommodate the differences in height at each point along the arches.
This has helped create the very distinctive look of the bridge from below. There are eleven of the transverse walls and the imaginary smooth surface connecting them describes a very interesting curve, as if the bridge has been twisted. It is certainly visually dynamic.
The transverse walls also vary in thickness. The three central ones measure 300mm, while rest are 200mm thick.
The deck itself is stiffened with longitudinal edge beams topped by parapets. Their combined size is 900mm deep and 500mm wide and they appear to merge with the arch crowns over the central 7m of bridge. The deck slab is 200mm deep, and the original concrete roadway 80mm deep. The lip of the parapet supports metal railings on the bridge, with concrete barriers on top of the abutment wing walls.
The Engstligen Bridge cost 60,150 Swiss Francs (1931) and was constructed in three and a half months. In accordance with Swiss practice, it was stress tested, by Professor Fritz Hübner (1881-1957) of the federal transportation department in Berne. He found that the bridge satisfied, and even exceeded, the theoretical assumptions.
The concrete strengths measured were 176 kg per sq cm for the first samples, 340 kg per sq cm after curing and 480 kg per sq cm in the deck slab (where 400 kg per sq cm had been anticipated). Load tests resulted in maximum arch deflections of 0.72mm at the top, and 1mm at the quarter points.
When visited in 2013, there was no evidence of restoration work.
Contractor: J Seeberger of Frutigen
Research: ECPK
bibliography
"Robert Maillart: Builder, Designer, and Artist" by David P. Billington, Cambridge University Press, 1997
"Robert Maillart, Beton-Virtuose" ed. Gesellschaft für Ingenieurbaukunst, VDF Hochschulverlag AG an der ETH Zürich, 1996, reprinted 2007
"Robert Maillart and the art of reinforced concrete" by David P. Billington, Architectural History Foundation, MIT Press, 1990
"Robert Maillart: Bridges and Constructions" by Max Bill, translated by W.P.M.K. Clay, Pall Mall Press, 3rd revised edition, November 1969
"Einige neuere Eisenbetonbrücken" by Robert Maillart, in Schweizerische Bauzeitung, Vol.107, pp.157-163, April 1936
www.swiss-timber-bridges.ch
Location

Engstligen Bridge (Spitalbrucke), below Adelboden