“For the typical span, the precast U beam was the most cost-effective solution on construction cost as well as long-term life-cycle cost.”

Rafael Foinquinos

 

Best Transportation Special Solution

Miami Intermodal Center–Earlington Heights Connector in Miami, Fla.

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As with most public projects, engineers of the Miami Intermodal Center (MIC) Connector–Miami Metrorail Earlington Heights Station Connector were faced with tight time and cost constraints, but they also faced the added requirement of designing a structure that was stiff enough to meet strict vibration criteria.

“For the typical span of 120 ft, the precast U beam represented the perfect solution in meeting these challenges,” says Rafael Foinquinos, PhD, PE, at URS Corp., the engineer of record for the project.

The 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, Foinquinos says.

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 guideway 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 guideway 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).

The engineers included special connections between the superstructure and the substructure for the single track sections to make the single U-beam system torsionally stable. This was accomplished by appending special concrete block extensions at the ends of the beams in the precasting yard, says John Robertson, vice president of business development for Standard Concrete Products in Tampa, the precaster for the project.

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.

The use of precast concrete was an economical choice for both the short and the long term.

“This bridge was constructed at an estimated half the cost of a similar precast segmental bridge, and was up to 20% less expensive than a similar steel structure,” Robertson says.

It will also be cheaper and easier to maintain than other designs, Foinquinos says. “The U-beam precast system has a low maintenance cost, is simple to inspect, and it provided a very pleasant aesthetic solution,” he says. “The U-beam system integration with a trapezoidal segmental box section provided a sense of structural continuity in the whole guideway structural system and blended perfectly with the highly aesthetically pleasant terminal station.”

PHOTO CREDIT

URS Corporation

PROJECT CREDITS


Owner: Miami Dade Transit, Miami, Fla.
Engineer of Record: URS Corp., Miami, Fla.
Precaster: Standard Concrete Products, Tampa, Fla.
Contractor: Odebrecht/OHL, Coral Gables, Fla.
Project Cost: $180 million
Bridge Length: Single Track: 5350 ft (1630 m); Double Tracks: 3856 ft (1175 m); multiple tracks: 598 ft (182 m)