Bridges on Prague Metro lines

As early as 1903 Jaroslav Marjanko submitted a proposal to bridge the Nusle valley with a steel arch construction. At that time, however, Pankrác was a less important locality, only slightly built up. An imminent increase in car traffic was not expected and the subsequently introduced tram line was able to handle the necessary connection with the city without any issues, so Marjanko's proposal remained unanswered. In 1926, the first competition for the Nusle Valley Bridge was launched. A second competition was launched in 1933, with a two-level bridge required. The upper level was to be used for road traffic, the lower level for an underground railway. Several other competitions were held in the following years, but the decisive national competition was announced on 15 December 1958. The location of the bridge was clearly determined by the two-way connection to the ring road.

The development of bridges had progressed considerably over the years and a beam bridge made of prestressed concrete was evaluated as the most suitable solution, as opposed to the previously recommended concrete arch bridge. If we consider that the development of prestressed concrete bridges began in the country around 1950, this means that in just fifteen years of design and construction, such a technical level had been reached in this area of bridge construction that it was possible to carry out this important and technically demanding work.

The prestressed concrete bridge forms one compact structural unit without expansion joints. It has five fields with theoretical spans of 68.25 m + 3 x 115.5 m + 68.25 m and, with 1 m overlaps behind the abutments, and the total length of the superstructure is 485 m. It is separated from the end abutments by two expansion joints at the ends. With them, the bridge has a total length of 603.30 m. The total width of the bridge of 26 m is used for two three-lane carriageways 3.25 m wide, two 2.50 m wide pavements including high safety kerbs and has a raised central dividing lane 1.50 m wide. The superstructure is rigidly connected to the four inner pillars and has sliding supports on the outermost abutments using swing walls. It rises with a longitudinal slope of 0.65 % from Karlov to Pankrác.

The competition conditions included technical data for metro cars with an axle pressure of 160 kN and tram cars with an axle pressure of only 105 kN. Later, in 1962, a government resolution adopted the concept of public transport with a subsurface tramway, according to which the design documentation for the bridge was prepared. However, only five years later a new government resolution was issued on 9 August 1967, in which it was decided to build the metro on the basis of recommendations from Soviet experts. By then, the construction of the Nusle Bridge was already underway. At the same time, two 2-piece sets of Czech-made ČKD Tatra cars with an axle pressure of 105 kN were delivered for trial operation. Eventually, however, heavier Soviet-made cars were purchased. To carry the unexpectedly higher load, a steel grating with a weight of 822 tonnes had to be additionally inserted into the tube of the finished bridge under the tracks.

The Nusle Bridge, although the most important bridge in the Prague metro network, is not the only one. Three other bridges are used by metro trains. On Line C, there is a bridge over the railway line just outside the Kačerov station towards the Roztyly station.

The other two bridges are found on Line B. On the line section Lužiny - Hůrka, the bridge structure crosses the valley of the Prokop brook. In terms of direction and height, the section is predetermined by the location of the stations and consists of two opposite curves with a radius of 350 m. The bridge structure consists of a continuous beam with nine spans of 30 m, 7x45 m and 30 m. Structurally, the bridge consists of a full-wall welded steel beam. The bridge columns are reinforced concrete, based on pile foundations. The bridge is enclosed so that the route is insulated from the weather and other external influences. The cladding is all-welded weathering steel with patinated, corrosion-resistant sides.

A 488 m long bridge structure is also located on the Rajská zahrada - Černý most section. The bridge has 15 spans and 16 abutments; the span lengths are 30 and 35 m. The bridge is a continuous girder with one fixed support; the other supports are sliding. The bridge is made up of a closed profile, so in this case the train traffic is also protected from all surrounding, especially climatic, influences. The bridge tube has a walk-on ceiling that is accessible to public pedestrian traffic.

An interesting bridge structure has also been designed for the newly planned Metro Line D. The platforms of Nádraží Krč station will be partly placed on the bridge. The bridge will cross the Kunratice brook in the immediate vicinity of Krč Chateau. It will be connected to the underpass of the rail head of the station at one end; on the other side, the line will pass under the Jižní spojka road.