Assessment of a statically indetermined existing box girder bridge subjected to settlements

In the R1 around Antwerp, the Merksem Viaduct is located. The viaduct was built between 1965 and 1969 and has been in use since 1970, making it over 50 years old. The Merksem Viaduct consists of a large number of spans, including the Bridge over the Connecting Channel called “Verbindingsgeul”. The bridge consists of two adjacent viaducts, with the superstructure of both viaducts consisting of 3 spans and 5 parallel box girder sections. As part of the Oosterweel project a new tunnel will be constructed directly next to the existing viaduct. While the construction work is being carried out, the existing viaduct must remain in use. Due to the construction of the tunnel, directly adjacent to the piers of the bridge, settlements will occur. Since the box girder bridges are designed as a statically indeterminate structure, differential settlement in both the longitudinal and transverse directions will result in additional forces in the bridge deck. This paper describes the assessment of the existing post-tensioned concrete box girder bridge with a 2.5D FEM model, including construction phasing, tensioning with prestress losses, shrinkage, creep and relaxation over the past 50 years and coming 10 years. With this verification calculation, the structural safety for the current situation could be demonstrated, and the sensitivity to settlements was made clear.