When highway A8 was expanded by an additional lane the existing arch bridge “Rotes Steigle” was replaced with a distinctive new structure, providing a crossing for a forest road over the highway. sbp’s design for the load-bearing structure of the new integral composite bridge comprises a lower arched steel box girder with varying cross-section dimensions, steel struts that are angled outwards, and a reinforced concrete deck slab. The slender construction was designed as a two-hinged arch that rests on stainless steel rocker bearings at the arch-support. The superstructure is supported on the arch by slender, inclined steel braces. The deck is monolithically connected to each abutment via a thin vertical steel plate acting as an elastic spring (height of approx. 1.10 m, thickness of merely 2 cm). To minimize disruption to the highway, the individual steel elements were pre-assembled into two large segments of 120 tons each and rapidly installed in only two nights. The concrete work on the deck could be carried out without the need for further interruptions to highway traffic. Due to the incremental production of the steel structure and the bridge deck, the fabrication and the execution of the construction work called for extensive deformation analyses and camber calculations. Specific measures that had to be taken during the construction include the pre-stressing of the arch and the subsequent casting of the abutment base and the lamella-spring support plates. Another special feature is the use of the latest generation of a new expansion joint system, which was applied at the transition joint between the superstructure and the abutment. Now, a slender steel arch structure presents a modern contrast to the previous bridge.
