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A current project to supply and install structural bearings for a heritage-protected railway bridge in Germany demanded a tailor-made solution to meet the various challenges arising.
The Hochheim Railway Bridge, which crosses the River Main near Frankfurt before it flows into the Rhine, was built in 1901 – 1903 with four structurally independent arches spanning the river. Almost 120 years later, after a colourful history that included major strengthening in 1936 and being partially blown up in 1945 (and repaired in 1946 – 1947), renovation work is currently being carried out. This work includes replacement of the eight bridge bearings that support the two longest river crossing spans.
Structural bearings of the RESTON®SPHERICAL type were selected for use, due in part to their ability to carry high loads in a compact unit and to facilitate large multiaxial rotations. The spherical bearings were designed for vertical loads of over 10,000 kN and longitudinal movements of +/- 95 mm. Half of the bearings, of the free-sliding (KA) type, were further designed to accommodate transverse movements of +/- 10 mm, while the rest, of the guided-sliding (KE) type, were designed to resist transverse forces of over 1000 kN.
For optimal load transfer, and to optimally match the shape/appearance of the existing elements that were to be removed (satisfying conservation requirements), the bearings were designed to be installed “upside down” (with the sliding plate on the bottom), with suitably designed transition elements, of steelwork and composite steel/concrete, above and below the bearing respectively.
One particular challenge affecting the installation work, which is also being carried out by mageba, relates to the time available on site, with the demolition and installation work for all bearings required to be completed during two weekend closures of the bridge to railway traffic (Friday 11pm to Monday 6am) – including curing of in-situ concrete etc.
Another significant challenge is posed by access, with most of the bearing locations requiring the work to be carried out from barges on the water. And in working off the barges, it is required to ensure that shipping traffic on the river – especially under the end span of the bridge that leads to the lock at the nearby weir – is not affected for more than an hour at any time.
When the new spherical bearings have been fully installed, the bridge will be much better equipped to deal with the challenges it will face in the future – not only because the structural bearings are new and in perfect condition, but also because the modern bearing technology used will enable constraint forces that would resist desired movements to be minimised, and also enable rotations about a transverse axis to be accommodated without damaging constraint forces arising. And mageba is proud to be able to prove once again that it can be trusted to design, deliver and implement state-of-the-art solutions to meet the most demanding bearing requirements of any special structure.
Bridge designer: Johann Caspar Harkort
Contractor: DB Netz AG, Regionalbereich Mitte
Bridge owner: Preussisch-Hessische Eisenbahngemeinschaft
Schematic drawing of one of the new spherical bearing types, showing a longitudinal cross section on the left and a transverse cross section on the right. The new steelwork element above the bearing can be seen, as can the composite element below the bearing (steel trough filled with reinforced concrete, with block-outs for the bearing’s four anchors to be filled on site)
Image: © Büro Krebs & Kiefer