New Langensand Bridge in Lucerne, Switzerland: Evolutionary System of a Composite Structure

The urban development of the city of Lucerne required the replacement of the existing Langensand road bridge by one designed according to modern standards of urban mobility. The bridge’s shape is the result of a synthesis between function, construction method, structure, and the urban context (extremely dense environment and several complex constraints). The bridge crosses 79.7m with one single span girder over 11 railway lines. Its composite structure has an extreme slenderness of about L/37. The paper describes the advantages and problems of a steel-concrete composite construction especially in regard to its structural system, and the evolution during the construction phases, and to its slender and flexible structure. The paper will compare and highlight the theoretical approach (hypothesis and numerical models for static and dynamic actions) with the results of in situ tests for the two principal states of the structure: firstly, the half bridge and secondly, the final connected bridge.