Structural design and engineering of Striatus, an unreinforced 3D-concrete-printed masonry arch bridge

This paper describes the structural design and engineering of “Striatus”, a 3D-concrete-printed unreinforced masonry pedestrian bridge built in Venice in 2021 as part of the Time Space Existence exhibition organised by the European Cultural Centre. The project combines the latest developments in 3D concrete printing with the structural principles of historic unreinforced masonry. Typically, the structural applications of 3D concrete printing are limited to elements such as columns and walls loaded vertically, perpendicularly to the horizontal printing layers, to formwork elements or secondary structural elements. Indeed, fabrication constraints, delamination issues and the low tensile strength of the concrete have been seen as limiting factors to 3D concrete printing for structural applications demanding resistance to bending or predominant loading directions not perpendicular to the printing layers. By using unreinforced-masonry structural principles, this paper shows that structural elements spanning space horizontally, such as a pedestrian bridge, can be built by using the 3D concrete printing components as the main structure, working only in compression, loaded perpendicularly to the printed layers. Furthermore, as a compression-only structure following masonry principles, Striatus enabled the use of unreinforced concrete without any mechanical or chemical connections between the elements and the separation of concrete and steel, only used for the supports and to equilibrate the horizontal thrust of the arch effect through the tension ties. This work shows how the application of unreinforced masonry principles to 3D concrete printing offers new opportunities in terms of structural design and represents a strategy to increase sustainability by reducing material consumption and allowing reusability and recyclability of the structure. Finally, this paper discusses the critical aspects related to the design of Striatus from an engineering and construction point of view.