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Lorraine Bridge
River Aare, Berne, Berne canton, Switzerland
Lorraine Bridge
associated engineer
Robert Maillart
Ingenieurbureau Maillart
date  February 1928 - 17th May 1930
era  Modern  |  category  Bridge  |  reference  Tf182159
photo  copyright ETH-Bibliothek Zürich, Bildarchiv
The architectural style of the concrete block Lorraine Bridge (Lorrainebrücke) in Berne is known as Heimatstil or 'home style', which was popular in Switzerland in the first half of the twentieth century. The bridge is one of 13 major structures over the River Aare in the city, and connects the old town with the suburb of Lorraine. It was repaired in the 1940s and remains in continual use.
The Lorraine Bridge was built to take car and foot traffic previously carried by the then-adjacent Red Bridge (Rote Brücke, built 1858, demolished 1941) — a high-level continuous iron girder bridge on stone piers, with a railway upper deck and roadway lower deck. By the 1880s, development into newer areas of Berne had meant increasing traffic volumes on the Red Bridge’s roadway.
A competition for the design of the bridge was held in 1897. The winning engineers were Robert Moser (1838-1918) and Gustav Mantel (1853-1908), who proposed a huge stone arch, spanning 60m. It wasn't built, perhaps because another road bridge was under construction about 0.5km to the east.
In 1911, a second competition was launched. Engineer Robert Maillart (1872-1940) and architect Joss & Klauser submitted a tender but their proposed concrete arch lost out to a masonry design from a consortium led by engineer Albert Buss (1862-1912). Moser, a proponent of stone bridges and traditional construction — and no supporter of Maillart — was on the judging panel.
World War I (1914-18) intervened and nothing was done until 1923, when Berne's building department decided to look again. By this time, the rail capacity of the Red Bridge was also inadequate and the relative merits of separate vs. combined road and rail bridges were being considered.
In March 1924, Maillart presented some new ideas. Adolf Bühler (1882-1951), director of the bridge division of the Swiss national railway system, soon submitted an alternative. After lengthy deliberation, in December 1925, the building department chose the design developed by Maillart working with Klauser & Streit (successor to his 1911 architect).
During 1927, the final design was approved by the holding of a referendum in Berne. The budget set at 3.8m Swiss Francs. Maillart decided on concrete block construction, giving the bridge a traditional form similar in appearance to the masonry Nydeggbrücke (opened 1844, the first high-level bridge in Berne).
The Lorraine Bridge is 178m long, with a deck 19.9m wide over the river and 21.5m wide elsewhere. An elliptical arch 16m wide crosses the river, with a clear span of 82m and rise of 31m (37.5m above the water). A smaller semicircular arch flanks each side of the man arch — 16.1m span on the west and 16.5m on the east. The arches and spandrel walls are constructed in concrete block. The spandrels hide a vaulted superstructure divided by slender transverse and longitudinal reinforced concrete walls into a series of vertical rectangular closed cells between deck and arches.
The main arch is 1.2m thick at the crown, increasing to more than 13m thick at the haunches, which are founded on bedrock. Above the arch, the hollow vaults are arranged in rows five cells wide, with rows of seven cells where the bridge widens over the supports and abutments. A corridor 2.5m square runs the length of the bridge, just below the road deck, with openings into other parts of the superstructure.
The western abutment is 20.2m wide and consists of seven vertical cells founded on three concrete walls 9m long and 2.8-3.2m wide. The walls are up to 21.7m deep and penetrate through the filled ground of the existing embankment and underlying marl into the bedrock.
The 20.2m-wide eastern abutment has two rows of seven cells, one above the other. It is constructed within the existing embankment and supported on a stepped concrete pad up to 5m thick founded in solid moraine. The hollow construction and pad footing were chosen to reduce the weight of the abutment, as the ground could only support a bearing pressure of 392kN per sq m.
The eastern approach (south side) is carried on a retaining wall, fronted by a series of arches adjacent to the botanical gardens next door. On the north side of the approach, a railway embankment led to the Red Bridge.
Construction began in February 1928. First, a low-level temporary bridge was built to transport excavated material, falsework timber, concrete blocks, concrete and reinforcement via a double cable crane of 2 x 3 tonne capacity. Concrete was batched and blocks were made at two downstream plants, one on each sloping bank, laid out so that the gravel and sand silos could be loaded at street level.
Preparatory works were complicated by the proximity of the Red Bridge, the foundations of which were shallower than the ones for the new bridge. Excavations for the new footings were undertaken in sections, with each void formed quickly filled with mass concrete. No piles or shafts were driven.
Timber scaffolding for centring the main arch was erected in September 1928, using the cable crane to lift pre-assembled sections. The arch was laid on a curved timber form carried by three pairs of fan-shaped supports. The base of each support was mounted on a hardwood block embedded in concrete, resting on a sand bed. The sand was allowed to trickle out of the bed to lower the centring once the arch was completed. To prevent malicious or accidental removal of the sand, the bed was covered and anchored by wooden sleepers.
The first ring of blocks was laid on 3rd-20th November 1928, along the arch centreline. Blocks were positioned alternately vertically and transversely, with 20mm thick mortar joints between them. The completed ring of blocks not only acted as a key for the adjacent rings to interlock with but also helped to support the weight of the arch, reducing loading on the centring and enabling the temporary works to be lighter and less expensive.
Work on the arch and surrounding parts continued into 1929, halting during cold weather in February. By June 1929, construction of the spandrel walls was underway. In July, the vaulting and through corridor were completed and construction of the bridge deck began.
The masonry-like finish on the spandrel walls was achieved using the Contex process to expose the aggregate. Careful choice of aggregate and coloured cement produced a greenish tone similar to Berne sandstone. In addition, the bearing surfaces of the arch and spandrel concrete blocks were given Contex treatment to improve adhesion in the mortar joints and mitigate against sliding.
The bridge deck slopes at 0.6% and is 1.06m higher at the east end. It was built with an 11m wide roadway, with walkways on each side. The pavements were 3.5m wide over the river and 4.3m elsewhere. Full width over the main arch is maintained by projecting the walkways 650mm, supported on concrete corbels.
Deck reinforcement was placed in August 1929, and the slab was cast in situ — 230mm of mass concrete topped with 60mm of reinforced concrete. The pavement slabs are of Ticino gneiss with kerbstones of Grimsel granite. Gaps beneath the pavement slabs, over the corbelled walkways, were left open to allow alpine swifts to use the spaces as nest boxes.
The quality of the concrete used on the project was checked throughout by making and testing 200mm concrete cubes and 200 x 200 x 600mm concrete prisms. When the bridge was completed, its strength was verified by load testing, a approach commonly used in Switzerland for assessing structural performance.
On 6th October 1929, before the road was surfaced, load tests were carried out under the supervision of Professor Mirko Roš (1879-1962). The loads were provided by eight trucks and a tower crane, totalling 114 tonnes. Vertical deflection, horizontal movement, rotation, stress and vibration were measured with the loads in 10 different positions using 46 instruments. The maximum recorded vertical deflections were less than 0.3mm and the horizontal movements were around 0.1mm.
On 2nd November 1929, the timber scaffolding was struck and the arch centring began to be lowered. Pedestrians were allowed to cross from December 1929 and the bridge was opened to traffic on 17th May 1930, following a gala procession and an inaugural speech by Maillart.
The actual construction cost of the bridge was 2,563,000 Swiss Francs, with 392,000 Francs for approaches and landscaping. The total, under 3m Francs, is much less than was allowed for in the 1927 referendum.
In 1941, the Red Bridge was demolished. Its replacement is the Eisenbahnviadukt Bern (Berne railway viaduct, built 1937-41), which was the largest concrete arch bridge in Europe at the time.
In the late 1940s, the eastern approach to Maillart's bridge partially collapsed when work on a conservatory in the botanical gardens, immediately south of the bridge, caused four of its supports to fail. In 1968, the roadway was widened by 1m each side, making the pavements narrower. The bridge now carries two lanes of vehicular traffic in each direction.
Architect: Klauser & Streit
Supervising engineer: Albert Huber
Resident engineer: Ernst Stettier
Contractor: Eugen Losinger & Cie AG
Reinforcement: von Roll'schen Eisenwerke
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 [in German]
"Robert Maillart's bridges: the art of engineering" by David P. Billington, University Press, Princeton, New Jersey, 1979
"Die Lorraine-Brücke über die Aare in Bern" by Robert Maillart, in Schweizerische Bauzeitung, Vol.97, January 1931 [in German]
www.derbund.ch
www.digibern.ch
www.karl-gotsch.de
Location

Lorraine Bridge