Putting together 921 pieces to make a pair of bridges isn't easy, particularly when the parts weigh as much as 32 tons each. Yet it was done in record-breaking fashion when the Metropolitan Atlanta Rapid Transit Authority (MARTA) built the first concrete box girder rail structures in the United States. Other breakthroughs on the project included the first use of full-span, long-line precasting in the U.S. as well as the transverse prestressing of top slabs of the precast segments.
Twin erection trusses mounted on bridge piers provided temporary support for an entire span of box girder segments. After the segments were placed on the trusses by crane and winched into place, they were post-tensioned longitudinally with exposed tendons that run inside the box but not inside the concrete.
Joints between segments were match cast with multiple shear keys. No epoxy was used in the joints. Wings of the segments rested on movable supports on the upper flange of the triangular erection trusses so that an entire bridge span could be accurately positioned for post-tensioning.