Robert Maillart's key methods from the Salginatobel bridge design process (1928)

Fivet, Corentin [UCL] Zastavni, Denis [UCL]

This paper sheds light on some of the graphical methods used by Robert Maillart to design the Salginatobel Bridge, a three-hinged concrete structure spanning 90 meters. Built in 1929, this masterpiece has since received extensive recognition both for its structural elegance and its efficiency. However investigations into the design process enabling this degree of perfection remain incomplete. Studying Maillart’s original working drawings, this paper reviews the earliest stages chronology of the Salginatobel Bridge design process. It focuses on three methods: the use of graphically controlled parabolas, the minimization of bending moments within the bridge and the geometrical definition of the foundation block. These graphical methods reveal how Maillart simultaneously dealt with geometry and the flow of forces throughout using a straightforward, handy and efficient form-finding process which is still relevant today.