Pöcking

The Pöcking bridge replaces an old bridge (built in 1900) crossing the Munich-Mittenwald railway line. It is part of the road link from Pöcking to Possenhofen.

Concept

Railway headroom and road level requirements did not allow a significant change from the construction depth of the old bridge. Only very short rail traffic disruption was acceptable while road closure periods had to be minimised. These constraints heavily influenced the design.

Composite construction and the use of partially prefabricated deck girders provided the solution. The new bridge has longer spans than the old one. The longer spans made it possible to substantially reduce the dimensions of the retaining walls of the abutments. This helped to optimise the cost of the new bridge.

Key benefits of using steel

Reconstruction of the old bridge had to be carried out under severe geometric and construction constraints. These constraints are typical for this type of project.

The constraints were overcome through integral bridge design, an innovative shear connection technique, and partial prefabrication. The new design achieved overall cost effectiveness, a short construction time with minimal traffic disruption, and reduced need for future maintenance.

Design details

Three main girders carry the 10.35 m wide deck. Each girder is made of two rolled T-sections with an upper 3.2 m wide prefabricated concrete flange and concrete filling between the T-sections. Shear connection between steel and concrete, required for composite action, is achieved through the shape of the web edge. The numerous openings resulting from S-shaped cutting line in addition with transverse reinforcing bars act as shear connectors. Benefits of this technique are low fabrication costs, material saving by elimination of the upper steel flange and high fatigue resistance.

The bridge is designed as an integral bridge with frame abutments and a low-stiffness spring plate connection to the intermediate pier. The elimination of the costs of maintenance and replacement of bearings and movement joints achieves whole life cost savings.

Construction details

Tasks such as cutting T-sections out of rolled beams, cambering to compensate for dead-load deflection, assembling by pairs, and application of corrosion protection were carried out at the finishing department of the rolling mill. Concrete flanges were added at a prefabrication shop.

After transport to the site by road, the three prefabricated composite beams (32 x 3.2 m) were erected with a mobile crane. Rail traffic disruption was restricted to six hours. The concrete flanges provided sufficient stiffness to prevent lateral torsional buckling. Temporary bracing was not needed.

To complete the deck slab, concrete was poured on the prefabricated flanges which were used as permanent formwork. At the same time, the ends of the beams were encased in concrete to realise moment connections.

Summary