Where underpasses under rail lines must be constructed or renewed, developers as a rule, aim to reduce track possession to a minimum. These are the times during which rail traffic must be blocked, and such measures are frequently taken locally. In such cases, however, prolonged track possession cannot in most cases be avoided, due to the complex auxiliary structures that must be erected before installation can take place.
Precast reinforced-concrete frame members
Here, the responsible parties decided on the use of precast reinforced-concrete frame members. The old overhead crossing in the eastern part of Duisburg had been in need of rehabilitation for a longer period of time, both technically and economically. The planners had originally intended to manufacture the new reinforced-concrete semi-frames locally and to subsequently install them in their final position by lateral displacement. The frame structures were to be pushed into place during short track possession in order to interfere as little as possible with regular rail traffic.
B.Eng. Henning Herbers – site supervisor of the building contractor Hofschröer GmbH & Co. KG from Lingen. Germany – explained why the project, in the end, was implemented in a different way: “For the planned newbuild, it was necessary to demolish part of the existing bridge construction. Due to the cramped conditions between the railroad embankment and the sewer pipeline routed there, south of the city of Duisburg, temporary shoring of the southwest and southeast sections of the railroad embankment had originally been planned in the form of a reverse-anchored retaining structure. This however, was not possible, since prospecting shafts that had been sunk evidenced that the sewer pipeline, other than stated in the tender documents submitted to us, run farther to the north of the structure. This situation meant that the displacement process described in the invitation to tender, as well as the planned reinforced-concrete works, could not be carried out,” Herbers explained.
Precast reinforced-concrete elements up to 51 tons
The planners, together with the client, DB Netz AG, worked out an alternative solution. This provided that the complete structure, other than the original in-situ-concrete solution, would be delivered as a construction set of precast components to be assembled at the construction site. At the construction site, a mobile crane was used to install a total of 19 structural components with a maximum width of 4.80 m, a maximum length of 8.25 m and an individual weight of up to 51 tons, as delivered by the company Kleihues Betonbauteile GmbH & Co. KG from Emsbüren, Germany.
For this procedure, the full frame was basically manufactured from three large-dimensioned reinforced-concrete frame sections and 12 wing walls of reinforced concrete. After installation, the sections were glued with epoxy resin, braced together and forced-locked for installation in their final position.
Construction without auxiliary bridges and without temporary retaining
Reduction of the worksteps
Yet another advantage of the precast construction method makes a major difference: “Precast components are manufactured in the plant under controlled conditions and are subject to continuous quality control,” declares Dipl.-Ing. Paul-Martin Grosskopff, Managing Director of Kleihues, the manufacturer. “This typically results in enhanced concrete quality compared to in-situ construction, and also offers visual advantages. Use of precast components, moreover, requires notably fewer steps of work. This can often simplify a construction project and reduce potential sources of error.”
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