Innovation in Bridge Engineering

In the area of structure 401b, a forest road bridge, motorway A3 west of interchange Nuremberg is being expanded. It wasn’t economically advantageous to renovate the old bridge, so it had to be replaced by a new structure. An innovative procedure was implemented: A steel trough fixed between abutments. In 2024, the bridge has been opened for traffic.

The new construction method entailing a steel trough and girders fixed between abutments was chosen as the preferable method as this only required a slight increase of the rural road’s gradient. The support-free crossing was implemented with two externally positioned steel troughs and a composite slab in-between at variable height. The narrowly rounded crest of the road is concealed in the front view by steel girders generously curved at the upper edge

The bridge is a slender, integral frame structure. The steel boxes are fixed to the abutments by top plates at the lower compression area. The upper compression area of the steel boxes is lengthened beyond the wing walls and suspended at their ends by steel reinforced concrete. The joint was filled by grouting mortar and self-compacting concrete in some areas.

In transverse direction, light filigree prefabricated composite slabs were placed on the steel girders’ supports. On top, a 0.23-metre-thick composite slab was grouted. The steel girders were fabricated at the plant of company SAM at half their lengths and placed on the pre-concreted abutments and a temporary support on motorway A3.

In 2024, construction was completed and the bridge has since been opened for traffic.