Miller Park, soon to be the new home of the Milwaukee Brewers, will feature retractable roof sections that unfold, like the petals of a fan, on tracks set atop a 1,050-foot-long curved concrete beam system. Project engineers chose cast-in-place concrete rather than steel for the curved beams for reasons of economy, simplicity, and aesthetics.

The concrete track-beam system is supported 150 feet above grade by eight steel towers at 150-foot centers, and the beams will span these towers without intermediate support. To achieve the required rigidity, the track-beam system's individual curved girders are 16 feet deep and 30 to 36 inches wide. Each moving roof section rides on its own girder. The curving girders are intersected every 12 to 16 feet by 18-inch-thick, 16-foot-deep connector beams.

The curved concrete girders are being cast in heavy-duty steel forms supported by trusses 150 feet above grade. Each form consists of stacked gangs of two 8-foot-high panels, along with filler pieces and corners. Panel lengths vary from 1 to 8 feet. Girder cross sections are all rectangular. However, the girders are not concentric, and the voids shaped by their intersection with the transverse connector beams are different sizes. Moreover, many of the corners are not right angles. Thus, the forms must be modified for each pour with different sizes of steel fillers. Workers lower the forms to the ground after each pour to modify them, and then lift them back up to their new locations.