Siebenlehn motorway bridge
The Siebenlehn motorway bridge (also known as the "Siebenlehn valley bridge") is an approximately 413 meter long girder bridge on the 4 federal motorway over the Freiberg Mulde . It belongs to the Dresden - Chemnitz section and is located in the small town of Nossen in the Meißen district in the immediate vicinity of the Siebenlehn district of Großschirma . The bridge, originally built in the mid-1930s, was the highest motorway bridge in Europe at around 70 meters above the valley floor. During the planning and execution, the structure also had the designation "BW 59" of route 83 (Chemnitz – Dresden).
planning
Several well-known companies, including the MAN plant in Gustavsburg , the Dortmunder Union , Krupp , Lauchhammer and Demag , submitted corresponding designs for the construction of a steel bridge (superstructure). The superstructure was to rest on stamped concrete pillars faced with natural stone or on pure steel pillars, as they were used, for example, in the construction of the viaduct over the Kleine Striegis . Companies such as Grün & Bilfinger and Siemens-Bauunion submitted designs in reinforced concrete.
The designs by Siemens-Bauunion and Dyckerhoff & Widmann should be mentioned, as the valley was to be bridged by a single reinforced concrete arch with elevated supports and reinforced concrete superstructure, similar to the Teufelstal Bridge near Hermsdorf (Thuringia) .
During the construction of the Reichsautobahn , the aesthetics of the structure in connection with the surrounding landscape and the recognizability of the forces acting on the structure played a decisive role. It was also of great importance to maintain a certain uniformity of the structures on a route, which should thus achieve a certain monumentality of the entire Reichsautobahn structure, especially through such large structures.
The design of the MAN plant in Gustavsburg was selected with the assistance of Grün & Bilfinger. It stipulated the superstructure with two continuous steel perforated metal girders (height of web plates 4.5 meters, length 402.90 meters) in Nietbauweise perform. This should be stored on five pillars and the two abutments (bridgeheads). This resulted in different pillar spacing, the main span was 81.60 meters.
A pillar-shaped stamped concrete pillars came with stone veneer of reddish Meissner granite for execution.
The western abutment is also remarkable in this design. With its wing walls, it reached a total length of 92.10 meters. This also gave the building a monumental character and integrated it better into the flat valley above in meadows and fields.
Since the motorway users at such structures were usually given the opportunity to visit them during a rest, a vaulted tunnel was led through the final structure. A viewing platform was also planned on the edge of the valley, south of the bridge.
Construction work
The work on the foundation, the pillars, the abutment and the deck slab were divided into two construction lots . Grün & Bilfinger was awarded the contract for section I (east side), and Siemens-Bauunion for section II (west). The preparatory work for the construction of the bridge began in September 1935 with the establishment of the construction sites. For this purpose, inclined elevators were installed from the valley floor on both valley slopes. Barracks, storage areas for building materials, concrete mixers, a power supply and lorries were built in the valley .
The building materials were supplied by a narrow-gauge railway from Nossen station .
The valley of the Freiberg Mulde served as a mining area for ores for centuries . Because of an ore vein , the foundation of Pillar III (on the way to the hut house) had to be placed at an angle to a depth of 27 meters. It thus followed the vein to be able to be founded on solid rock.
Based on the experience with Pillar III, subsoil investigations were carried out again on Pillar IV (on the Mulde river bed). At that time, however, the pillar was already 20 meters high. This began to settle unevenly now and precisely because of the core drilling, as, among other things, water inclusions were drilled into the rock due to the drilling and this gave way. Cavities, loose debris and wood - evidence of medieval mining - and a water source were also drilled. 254 cubic meters of concrete were injected into the 54 boreholes to stabilize the subsoil. In mid-March 1936, while the pillars were still being built, MAN began to assemble the steel superstructure from the west side. This was done up to the first pillar (Pillar V) by means of a support scaffold and from Pillar V onwards in cantilever construction with auxiliary supports between the pillars. The steel components were supplied by MAN, Gute Hoffnungshütte Oberhausen and Hein Lehmann Düsseldorf . The construction of the steel structure was followed by the application of the 24.60 meter wide reinforced concrete deck. The topping-out ceremony was held on November 23, 1936, just 14 months after construction began.
When building the bridge were
- 35,000 cubic meters of concrete
- 13,000 square meters of granite facing
- 8500 tons of cement and
- 3010 tons of steel (in the steel structure)
used.
Work was carried out in two and three shifts between 5 a.m. and 10 p.m. The opening ceremony of the route was made by Adolf Hitler . A grandstand was built for this in the Muldental, from which he gave a speech and then visited the building.
1945 shortly before the end of the war
Like many other valley and river crossings, this bridge too was to be blown up at the end of the war on May 5, 1945, i.e. only three days before the end of the war. For this purpose, German soldiers installed explosive charges on Pillar III in a cavity that had already been set up when the pillar was built. The place of the cavity in the pillar was recognizable by a granite stone, which was marked with a "U". The blasting could be prevented by the courageous intervention of the Huthaus innkeeper Reinhold Ehrlich, a restaurant in the valley not far from the bridge.
The bridge remained in its basic form until it was rebuilt in 1994. Only the rust protection paint on the steel parts, which was orange when the bridge was built, was later covered by a gray one. Otherwise, it remained with repair work, especially on the deck.
The six-lane expansion of the motorway
In 1994, in the course of the expansion or new construction of the BAB 4 on 6 lanes and 2 hard shoulder, preparations began to widen the bridge superstructure. The foundation and the pillars could still be used.
To the south, next to the old pillars, an auxiliary pillar was built. The steel trough (substructure of the new south carriageway) was installed in an assembly hall built on the eastern edge of the valley and pushed it in so-called “shots” using the incremental launching method by around 30 to 40 meters over the temporary pillars.
After reaching the west side, the reinforced concrete roadway was applied to the trough and the "temporary bridge" created in this way was connected to traffic in both directions.
Now the demolition of the old roadway and the steel superstructure of the old bridge began, as well as the preparatory work on the old pillars. The pier heads were widened and lengthened to accommodate the two new, wider superstructures. Here the northern carriageway was constructed using the same procedure as the southern carriageway and, after completion, was handed over to all traffic.
This was followed by the transverse displacement of the 413-meter-long southern carriageway from the temporary piers to the bridge piers and the connection to the traffic. The makeshift pillars were torn down or blown up. With the exception of various repair work, the construction work on the bridge was completed in 1997.
This construction project resulted in a contemporary structure that can cope with the volume of traffic.
literature
- Wolfgang Eilzer: Design and execution of the Siebenlehn motorway bridge . in: TU Dresden (ed.): 6th Dresden Bridge Construction Symposium - Proceedings, Dresden 1996, pp. 43–70 ( digitized ; PDF; 2.9 MB)
- Holger Svensson: Design and tender for the Siebenlehn motorway bridge. Concrete and reinforced concrete construction, February 1997
Individual evidence
- ↑ Saxony Atlas of the Free State of Saxony ( notes )
- ↑ Alfred Harendt: The landlord from the "Huthaus" , in: Die Null, Berlin 1966, p. 129
Web links
Coordinates: 51 ° 2 ′ 14 ″ N , 13 ° 19 ′ 0 ″ E