A good example of post-tensioned segmental construction is the Ely Viaduct in Wales. The highway design features a 2000-foot radius curve crossing the River Ely at an acute angle with a 538-foot-long twin-box girder. The 230-foot central span and 150-foot side spans were constructed by the balanced cantilever method.
Box section of the girder is about 16 « feet wide, with cantilevers extending to a total width of 39 feet. Overall depth of the segments is 12 « feet, and they are 7 feet long. Weights range from 54 tons for plain segments to 93 tons for the main pier diaphragm units. Shear keys were cast in the face of each unit. Accurate joining was assured by match-casting each unit against its immediate neighbor. The face of each unit was sandblasted just before being lifted into position, about 12 inches away from the previously placed unit.
A coating of epoxy adhesive was then applied to one face and the units were joined and temporarily held by stressing post-tensioning bars. A prop and tie system prevented overturning and assisted with alignment until the balancing segment could be temporarily stressed into position. Permanent stressing was then carried out for each pair with 13-strand tendons.