Strengthening of the Inn Bridge Obernberg-Egglfing

The Obernberg - Egglfing Bridge is an important border bridge between Austria (L510) and Germany (St 2117). It was constructed in 1963 as a post-tensioned concrete structure, designed as a double-T beam in the span and a box girder in the area of the supports. Characteristic of this period, the steel reinforcement was minimized in favour of a high level of prestressing, and 100% of the tendons are coupled at the construction joints. Due to cracks in the coupling joints, the condition of the structure was assessed through comprehensive structural and metrological analyses, adhering to levels 1 to 4 of the German guideline for recalculation of road bridges. By reducing the load on the structure to the load model BK30, in combination with coupling joint monitoring and alternative design approaches to describe shear load-bearing capacity, the interaction of bending in transverse direction and longitudinal shear, as well as torsional stiffness in level 2, the structural deficits were sufficiently limited to make an economical strengthening of the structure feasible. But also during the planning and installation of the various reinforcement elements, the existing structure presented unexpected challenges.