SAINT GERVAIS VIADUCT (VIADUCT OVER THE BONNANT):

Roadway structure utilising pre-stressed concrete and metallic diagonals, 240 m long with 3 spans (35 m, 170 m, 35 m):
• End spans: pre-stressed concrete box girder cast on curve.
• Central span:
- “lattice” type of mixed structure consisting of two longitudinally pre-stressed C80/95 concrete hollow-core slabs joined together by 2 layers of metallic diagonals in the S355 and S460 grades. 
- the upper concrete hollow-core slab is pre-stressed by means of balance beam cables 27T15S, 22T15S, and 19T15S.
- the lower hollow-core slab is also pre-stressed in the central zone of the span by splice cables 19T15S.
- the tightened diagonals are pre-stressed using cables 19T15S to 24T15S placed inside metallic tubes and anchored in the upper and lower hollow-core slabs.
- the central span is built by successive cantilevering of voussoirs cast on site in a mobile system. 

PIER (PROVIDING ACCESS TO THE VIADUCT):
 
“Pre-stressed slab” type of roadway structure, 32.50 m long with 2 spans ( 2 x 16.25 m), deck with plane curvature with a radius of 74 m, single 5% camber and profile along the slope of 7%.

Photos: Pierre COOK