The Miami Intermodal Center ( MIC) facility connects local and regional transportation networks to Miami International Airport, including Tri-Rail, Amtrak, buses, and taxis. For train-riding comfort, the project criteria required the vertical frequency of vibration of the composite section to be greater than 2.5 Hz. Choosing a high-performance precast concrete U-beam design enabled the team to meet the requirement for rigidity while still providing the service and strength limit states for the maximum span considered.
The use of precast concrete was an economical choice for both the short and the long term. The bridge was constructed at an estimated half the cost of a similar precast segmented bridge, and was up to 20% less expensive than a similar steel structure. The U-beam precast system provided a low maintenance cost, is simple to inspect, and it allowed for a very pleasant aesthetic solution.
The project consists of 72 in. (1830 mm) modified Florida precast concrete U beams for the typical spans, segmental precast concrete boxes for the long-span units of the guide-way structures, and a few spans of 24 in. (610 mm) cast-in-place concrete slab at the connection to the Earlington Heights Station.
Along the 2.5 mi (4 km) alignment, which consists of tangent, spiral, and circular curves, the precast concrete U-beam portion of the guide-way features 43 spans of single track section, 33 spans of double track section, and 5 spans of multiple track section. The total number of U beams is 129, with a typical length of 120 ft (37 m) and a maximum length of 133 ft (41 m). Each beam was then delivered via truck using a 19-axle dual-lane rig that easily transported the 129 short ton (117 tonne) beam the approximately 250 mi (400 km) from Tampa to Miami.