Chapter 4: The Construction Process of Segmental Bridges
Table 4-3: Sequence of Casting Steps for Aichtal Bridge
Day Monday Tuesday
Friday Saturday and Sunday
Activities Post-tensioning, stripping of formwork, incremental launching of segment Placement of reinforcement cages for bottom slab and webs, Installation of ducts and tendons, installation of interior web formwork Completion of formwork installation, concreting of bottom slab and webs Removal of web formwork, installation of interior top slab formwork, Placement of top slab reinforcement, ducts, and tendons Concreting of top slab Curing of concrete
Launching of the cured and post-tensioned segments required many personnel for supervision of all sliding bearings. An overall longitudinal slope of the bridge reduced the jacking forces necessary for launching. An overall curvature with radius 1,500 m in the horizontal plane and a constant 3.5 % cross slope of the bridge superstructure induced stresses due to restrained deformations during launching. Furthermore, the changing span lengths had to be considered in coming up with the prestressing program to optimize the tendon profile and prestressing forces.
A surveying program had been prepared to control geometry during all construction steps. Several fixed surveying points were located along the site. Overall, tolerances for deviations from the planned bridge geometry during casting and launching were less than 1.5 mm (Basse et al. 1985).
Falsework has been used in construction since ancient times, when Roman bridge builders erected their semicircular stone arches for bridges, aqueducts, and vaults on wooden centering. Falsework provides continuous support for the formwork that gives shape to the superstructure. In most cases falsework is used for cast-in-place concrete structures. It requires firm, relatively even ground on which it can be erected.