Illerbrücke Sigishofen

The existing structure (built in 1969) carries the B19 federal highway near Sonthofen over the Iller River. It is a two-span prestressed concrete superstructure with spans of 38.54 m and 37.46 m, respectively, and a structural height of 1.70 m (slenderness 22.6). The typical cross-section is a two-cell hollow box. The superstructure is supported at an oblique angle, lies in a radius of 1000 m, and widens by approx. 3.0 m in the northern field.

The recalculation we carried out in recalculation stage 1 revealed some massive static deficits. Parallel to the recalculation, some very high chloride contents were found in the concrete during an extended main bridge inspection, which was also carried out by us. The client therefore decided to replace the structure with a replacement structure as quickly as possible.

Since a closure of the structure was out of the question, it was necessary to prove the load-bearing capacity of the structure for the remaining service life. By applying the actual compressive strength of the structural concrete, a recalculation according to level 2 and by specifying structural tests on an annual basis, most of the deficits could be eliminated arithmetically. The shear force load-bearing capacity was finally demonstrated by a recalculation in accordance with level 4 of the recalculation directive using the pressure arch model, in conjunction with a downgrading of the structure from bridge class 60 to bridge class 30/30 and a change in traffic management on the structure. In addition, the shear force verification was carried out according to Herbrand’s approach, which is expected to be part of the 2nd supplement to the recalculation directive. The measures mentioned above made it possible to prove the load-bearing capacity for the remaining service life of the structure.