Coupling joint reinforcement of the "Sandacher" bridge with post-tensioned CFRP tendons – Spreitenbach, Switzerland

General information

The Sandacher bridge was constructed in 1969/70 and is a prestressed concrete structure that provides passage over the N1 national road, the Limmattal marshalling yard tracks, and the Dietikon-Killwangen line tracks, connecting Spreitenbach to the "Althard" area. The bridge is composed of 14 spans, each ranging from 19.80 to 32.70 m in length, resulting in a total length of 377.50 m.

The superstructure of the bridge has a width of 11.05 m, with 2.14 m on either side of the cantilevers. The bridge's maximum height of 1.26 m is located at its center. It is comprised of two parallel box girders that have a maximum clear height of 0.92 m. These girders are separated by three prestressed longitudinal girders that are typically 0.36 m wide.

Project

The Sandacher bridge has not undergone any significant rehabilitation work since its original construction. Therefore, the primary objective of the upcoming rehabilitation was to ensure the bridge's structural safety and serviceability. This includes achieving a maintenance-free service life of at least 40 years and a residual service life of the supporting structure of at least 60 years.

As part of the as-built surveys, it was discovered that all four coupling joints in the construction joint are cracked. These cracks are characterized by a single, constant crack width of approximately 1 mm. The crack runs along the lower box girder slab and tapers in the lateral webs towards the top.

Solution

To ensure the structural safety and serviceability of the bridge, all existing cracks at the coupling joints have been repaired. This has been achieved through the injection of the cracks and local overlay using the CarboStress? systems, with approximately 4’000 kN per joint. To further strengthen the structure, 18 CarboStress? systems, each with a tensioning force of 220 kN, have been installed per coupling joint.

Due to the lower box girder slab being only 14 cm thick, force application is staggered in the longitudinal direction. The tensioning systems have lengths ranging from 6.50 to 10.50 m and are attached to the underside of the box girder slab using mechanical anchorages.