South Watt Avenue LRT Grade Separation
This five-span, 539-ft-long bridge carries two light rail tracks over a heavily congested corridor and is in close proximity to a freight rail line. The all-precast through-girder superstructure consists of three precast/prestressed girders spanning in the longitudinal direction, and precast/prestressed concrete slabs spanning between adjacent girders in the transverse direction. The longitudinal girders were post-tensioned following the erection and stressing of the transverse slab tendons.
The sides of the trough are formed by allowing the supporting girders to project above the deck; this is in contrast to conventional deck sections that are supported from below. As a result, the structure depth required for a trough section is substantially less than for the conventional types. This allows the profile grade to be lowered, and avoids all costs associated with a raised profile.
The structure highlights an important benefit of precast concrete that is often overlooked: how the all-precast cross section itself was transversely integrated into a “super girder.” This concept opens the door for a new generation of all-precast super girders that are fabricated in segments, transported, and then field assembled into a single deck element. The additional flexibility afforded by such systems enables them to economically meet a wider range of functional requirements than conventional precast systems.