Design and production of an experimental UHPFRC bending-active footbridge

This paper describes the design, production and testing of an experimental footbridge made of ultra-high-performance fibre-reinforced concrete (UHPFRC). The prototype has a span length of 5.4 m and is made of a very slender pre-stressed UHPFRC deck (6 cm deep, 1.2 m wide), a 0.55 m high central deviator of the same material, and an external lower tensioning stainless-steel cable system. The service configuration of the structure involves a significant permanent bending of the deck, because of its slenderness; this initial bending is introduced in a controlled manner during the production process and prior to the installation, and results in an efficient, lightweight, and elegant structure with a high stiffness-to-self-weight ratio. The structural concept belongs to the category named active bending, which has been recent subject of research. Specifically, the structure is a bow-string system in which the bending-active member is made of UHPFRC, which constitutes the main novelty of this research. The suitability of UHPFRC as a material for bending active applications has been investigated, and a method to determine the limiting pre-stress of UHPFRC bending-active cross sections has been developed. The activation process and relevant limit states have been checked by means of a 3D frame finite-element model. The paper concludes with the description of the production process and the installation of the footbridge in the final location, as well as the successful results of the load tests and the geometric control of the novel footbridge prototype.