Grünwalder Isar Bridge

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Coordinates: 48 ° 2 ′ 35 "  N , 11 ° 30 ′ 58"  E

Grünwalder Isar Bridge
Grünwalder Isar Bridge
The old Isar bridge
use Road bridge
Crossing of Isar
place Grünwald
construction Reinforced concrete arch bridge
overall length 220 m
width 8 m
Number of openings 2
Longest span 70 m
Arrow height 12.80 m
Arrow ratio 1: 5.5
opening 1904
closure 1999
location
Grünwalder Isar Bridge (Bavaria)
Grünwalder Isar Bridge

The Grünwalder Isarbrücke (officially only Grünwalder Brücke ) is an arched bridge that connects the towns of Grünwald and Pullach south of Munich over the Isar , which flows in a deep valley . At the time of its completion in 1904, the first construction of the bridge was the largest reinforced concrete bridge in the world with the two 70 m arches.

Former reinforced concrete bridge

At the beginning of the 20th century, Grünwald and Pullach were still villages without a bridge connection, but the progressive expansion of Munich was clearly noticeable. In 1901, the year in which Sager & Woerner had agreed the bridge construction program for five Isar bridges with the city of Munich , Wayss & Freytag AG submitted an offer for a reinforced concrete bridge with two arches spanning 70 m each. The design came from Ludwig Zöllner, the static-constructive draft processing by Emil Mörsch .

At this time, the first beginnings in the construction of reinforced concrete bridges had been made, but it was not yet a mature technology. In 1893, Karl von Leibbrand first built a three-hinged arch in a massive concrete arch bridge at the Munderking Danube Bridge . This construction method was used again for the Pont de la Coulouvrenière, which opened in Geneva in 1896 . Wayss & Freytag AG had built the Münchner Kabelsteg in 1898 , a reinforced concrete bridge made of two very flat, fixed arches. For the Adolphe Bridge, which was built in Luxembourg from 1899 to 1903, Paul Séjourné erected a wide reinforced concrete deck on two narrower brick arches with a record span of over 84 m. François Hennebique built the Pont Camille-de-Hogues in Châtellerault in 1899 , the first reinforced concrete bridge in France. However, there were as yet no regulations or test procedures. Mörsch did not present his basic work “Der Eisenbetonbau, seineführung und Theory” until the following year, the first rules for the preparation, execution and testing of reinforced concrete structures appeared in Germany in 1904 and the German Committee for Reinforced Concrete , later the German Committee for Reinforced Concrete was only constituted in 1907. Mörsch himself was still at the beginning of his career when, barely 30 years old, he was planning the world's largest concrete arch bridge at the time.

In the summer of 1903, Eisenbeton GmbH , a joint subsidiary of Wayss & Freytag and the Munich-based Heilmann & Littmann company founded for this purpose , was commissioned by the communities of Grünwald and Höllriegelskreuth to build the bridge. It was a total of 221 m long. Two reinforced concrete arches with a span of 70 m each and a branch of 12.80 m spanned the Isar and the Werkkanal. The arches had cast steel joints in the fighters and the crowns. The arches with a rectangular cross-section were 90 cm thick on the fighter, widened to 120 cm at the point of maximum loads and tapered again to only 80 cm at the vertex joint. There were approach bridges on both sides of the arches, which were supported by pillars with a center distance of 10 m. The arches were dimensioned as unreinforced, exclusively pressure-loaded arches; some reinforcement was inserted only for safety reasons in the event of tensile stress. The elevation of the carriageway is carried out using slim supports with a cross section of 40 × 40 cm. The transoms and the pillars of the approach bridges were made of unreinforced stamped concrete. In August 1904 the falsework was lowered. After trial loads, the Grünwalder Bridge was opened to traffic on November 20, 1904.

In the following period, slope movements repeatedly required renovation of the approach bridges. Shortly before the end of the Second World War, SS units blew up one of the arches, which significantly impaired the balance of forces on the central pillar. Even after the reconstruction of the destroyed part, the structure suffered from movements of the subsoil and the resulting deformation of the arches. Weather-related damage and damage caused by road salt were added, so that the decision was made to replace the listed building with a new building since 1983.

Today's steel bridge

Grünwalder Isar Bridge
Grünwalder Isar Bridge
Today's Grünwalder Isar Bridge
construction Steel arch bridge
overall length 214 m
width 13.30 m
Number of openings 1/2 + 2 + 1/2
Longest span 37 m + 70 m + 70 m + 37 m
Arrow height 5.16 m
Arrow ratio 1: 13.5
opening 2001

In 1995 a competition was advertised across Europe which demanded that the design elements of the old bridge be retained in principle while demonstrating modern construction technology. The design by the engineering office Grassl and the architects Schultz-Brauns & Partner won. The new bridge was built between 1998 and 2001 by a joint venture made up of Bilfinger Berger and Voest Alpine MCE .

Based on the old bridge, the new bridge also has two arches spanned over 70 m each, but with a pitch of only 5.16 m, they are considerably flatter than those of the old bridge. Instead of the approach bridges, the two arches are supplemented by two half arches and connected to the slopes of the valley.

In contrast to the old bridge, the current bridge is a steel structure with a concrete deck. The steel construction, which runs through the four bridge fields, rests on three massive concrete pillars. On three parallel arches each, narrow steel bars serve as elevations for the roadway girders, which form a static bond with the concrete roadway slab on them. The three arched profiles merge at the apex with the profile of the deck girder. The 12.50 m wide deck protrudes 2.40 m from the girders on both sides. The steel structure is fixed to the central pillar by a retaining structure, while it is movably supported on the outer pillars. From a static point of view, the construction is described as a combination of an elevated arched structure and a truss structure with a distinctive frame effect.

Grünwalder Isar Bridge

The continuous landslides, especially on the Pullach side, were taken into account by designing the abutments as concrete boxes several meters in size, open towards the bridge, and being based on bored piles. As a result, they are fixed in the sliding mass above the slip plane and move horizontally with the sliding mass under the sliding bearing of the bridge. The sliding plates in the abutments are expected to be long enough to accommodate the movements of 140 years. The carriageway crossings between the road and the bridge carriageway were dimensioned for the changes in length over the next 35 years, after which a minor renovation is required in order to be able to accommodate further landslides. The western pillar can be moved in a locked shaft that can also move with the sliding mass.

The new bridge was initially built on temporary supports above the old bridge and opened to traffic in September 1999. After the demolition of the old bridge and the construction of the new piers and abutments, the bridge was moved transversely into the position of the old bridge in April 2001.

Web links

Commons : Grünwalder Brücke  - Collection of images, videos and audio files