A view of the Signature Bridge Arch 5 as Archer Western-de Moya Joint Venture nears final erection in August.
Photo by Nicole Bryant, the Corradino Group/Courtesy FDOT

For the overall project, and especially the Signature Bridge, Oscar Gonzalez, senior community outreach specialist for the state DOT, notes that the team makes extensive efforts to keep the community apprised of the project’s progress on current and future activities via its project website and weekly emails to roughly 4,000 subscribers, he says.

Monthly stakeholder meetings, open to the public, attract representatives of local venues—such as the nearby performing arts center—and elected officials, he adds.

With three of the bridge’s six arches now erected in the heart of Miami, the complex design remains in the spotlight for the builders.

Architect Donald MacDonald drew inspiration for the bridge from the Magic Fountain of Montjuïc in Barcelona, Spain
Photo courtesy Getty Images

Some additional materials quantities help illustrate the bridge’s broader scope: 288,646 cu yd of cast-in-place concrete; 95.1 million lb of rebar; 10.9 million lb of post-tensioning; 1,187 square piles; more than 583,000 cu yd of earthwork; and 136 stay cables.

Building More Than a Bridge

In addition to the bridge, the Archer Western-de Moya Group joint venture is also reconstructing portions of Interstate 395 (left), and segments of Interstate 95 (right).
Photos (left): by Nicole Bryant, the Corradino Group; right, courtesy Florida Dept. of Transportation

In addition to the bridge, the overall I-395/SR 836/I-95 Design-Build project will reconstruct 1.4 miles of I-395, from the SR 836/I-95/I-395 Midtown Interchange to the MacArthur Causeway, expanding capacity on I-395 via three through lanes in each direction and providing separate connector ramps for traffic to and from I-95.

The project will also modernize the SR 836 corridor from NW 17 Avenue to the Midtown Interchange by double-decking SR 836, providing a direct connection to the MacArthur Causeway. This structure will begin east of NW 17 Avenue, rising above and along the center of SR 836, then ending at I-395, east of the I-95 interchange, according to FDOT.

The direct connection to the MacArthur Causeway will be free of local entry and exit traffic, with the existing SR 836 roadway and bridges serving as a collector-distributor system enabling drivers to enter and exit from the local roads and I-95. According to FDOT, this system will reduce existing weaving movements, enhancing safety.

On the nearby I 95, from NW 8 Street to NW 29 Street, crews are replacing concrete pavement for the north- and southbound travel lanes, and adding an auxiliary lane along northbound I-95 from north of NW 17 Street to NW 29 Street to handle additional traffic from the eastbound SR 836 ramp to northbound I-95.

Additionally, the City of Miami has plans to build a mile-long I-395 Underdeck and Heritage Trail, a public landscape “that weaves below the elevated I-395 roadway, creating a 33-acre urban open space and streetscapes that will reunite the urban fabric of Overtown, a historically Black neighborhood that was disconnected during highway construction in the 1960s,” according to the city.

The City of Miami had secured a $60-million U.S. Dept. of Transportation grant for the estimated $82.7-million project, but the Trump administration in August rescinded that funding.

While calling the loss a significant setback, Miami city officials told media that the city remains committed to building the project.

Designing, Engineering ‘The Fountain’

The six-arch bridge structure, named The Fountain, will span 1,025 ft, with the tallest arch, Arch 5, rising 325 ft, with a width of 650 ft. The roadway will be supported by twin cast-in-place box girders suspended from each arch.

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HDR, engineer of record for the bridge and the I-395 work, describes the bridge project on its website as showcasing “the essence of Miami as the center for the arts, with this structure as its nexus,” adding that it “is inspired by Miami’s world status as the center of the Americas, and the fountain-like arches are symbolic of Miami as a place where people from all backgrounds come together and live as a community.”

 

Visualization illustrates the positioning of all six arches and the west- and eastbound superstructures; rendering shows layout of segmental bridges and typical roadway segments.
Bridge Rendering courtesy HDR; Bottom Image courtesy Florida Dept. of Transportation

The precise vision for the centerpiece arches came from the titular principal of San Francisco-based Donald MacDonald Architects LLC, who told ENR he viewed the assignment as “a wonderful opportunity to do something … that needed to be done.”

MacDonald—who credits HDR for the two parties’ “close working relationship” during the design phase—says he drew particular inspiration from two disparate elements: the logo of the former Miami-based Pan American Airways, and the Magic Fountain of Montjuïc in Barcelona, Spain.

“I used to fly Pan Am a lot, and they had logos that had these arches coming out from South America and North America and ending up in Miami,” he says. “That started me thinking. And then I wanted to get something that was the center for a city, and I found that Magic Fountain in Barcelona [had] these huge fountains in the middle of the city.”

When completed, LED lights “will go up the arches and come down the cabling,” MacDonald says, adding that there may be “four or five levels of interpretation” of the artistic bridge’s design.

“There’s different ways to look at this,” he says.

An early view of the 325-ft-tall Arch 5’s construction shows the structure’s size and the angle of its precast segments
Photo by Nicole Bryant, the Corradino Group

Archer Western-de Moya readies a precast segment for placement.
Photo by Nicole Bryant, the Corradino Group

The rising structure rests upon a center pier footing comprised of approximately 5,000 cu yd of concrete and 1.7 million lb of steel reinforcing that carries the weight of the arches and suspended deck, and houses the bridge’s electrical and structural health monitoring system, according to HDR.

The superstructure box girders are being built concurrently with the arch construction as cast-in-place structures supported on falsework. Once the arches are completed, cable suspenders consisting of 19 to 55 high-strength steel strands per cable will be installed, transferring the superstructure weight to the arches.

Mike Lamont, HDR major bridges technical director, says designing the arches proved uniquely challenging. There was little to no opportunity to tweak the bridge’s aesthetic details once the Miami’s design committee approved the project.

“The form of the structure is to satisfy an aesthetic vision, which is what the community wanted,” Lamont says. “It’s our job to make it work structurally.”

Typical arch bridges are uniformly loaded and “mostly working in compression,” he notes.“There’s no symmetry in [this] structure. Cables are pulling on the arches from different angles, which results in a lot of bending in the arches that is an unconventional loading condition for an arch.

“We needed a lot of post-tensioning in the arches to keep the segment joints in compression—and because of the lack of symmetry, that post-tensioning was not always a symmetric layout,” he adds.

A view of the ends of post-tensioning tendons at the roof of a center pier’s leg.
Photo by Scott Judy

A precast segment ready to be erected.
Photo by Scott Judy

Crews at work building the Arch 3 footer.
Photo courtesy Florida Dept. of Transportation

For example, “Depending on where you are in the arch, and which way the cables are pulling, you may have post-tensioning on one side and not the other. So we had a very intricate layout of post-tensioning through each of the arches based on their specific loading conditions,” Lamont explains.

As a result, some precast segments feature interior anchorages “on just one corner and not all four, or on one side and not the other,” he adds. “It’s not just the final condition we’re designing for; it’s all of these intermediate construction stages.”

Another factor the engineers had to consider was FDOT’s requirement that the bridge withstand winds of up to 140 mph throughout construction.

Calling the 140-mph standard “a very restrictive requirement” that also “makes sense,” Lamont says that “at each stage of construction, we have to make sure that we can withstand that wind loading, plus all the loads that result from building the structure.”

Carrying the weight of the arches and suspended deck is a center pier footing comprised of approximately 5,000 cu yd of concrete and 1.7 million lb of steel reinforcing.  
Photo by Nicole Bryant, the Corradino Group

For precaster Rizzani de Eccher, the signature bridge’s design made it next to impossible to standardize precast segment fabrication to any notable degree.

Normally, “we achieve fast cycles, and we achieve high efficiency in precasting,” says Paolo Longobardi, vice president of operations. But The Fountain is “a very different animal. These six arches are all different by design, by geometry [and] the loadings on these arches are very asymmetrical. We have arches where you see a lot of post-tensioning on one side and less on the other side.”

Arch 5, the tallest of the bridge’s six arches, rises 325 ft high, and extends 650 ft.
Photo by Nicole Bryant, the Corradino Group

The time it took to cast segments was “much longer than typical,” Longobardi adds, noting that the company completed “very few segments” on the more standard two-day cycles. Some segments “were taking four days, up to a week.”

Though there were change orders related to the precast segmental construction and erection, Mark Croft, CEI resident engineer with the Corradino Group, says most items were approved relatively quickly.

Lenny Gardino, senior project manager at Archer Western parent, the Walsh Group, overseeing segment erection, says that erecting the precast segments—as was the case with Rizzani de Eccher—proved to be more difficult than expected.

“It wasn’t just the congestion of the rebar; it was also the congestion of the post-tensioning running through those arches,” he says, calling the shop drawings “a task in themselves.” There were no typical segments that could be nearly duplicated with minor changes.

“We pretty much had a rendering of every single segment, and each stick of rebar was designed to be a certain angle, a certain length, to take on all the post-tensioning,” Gardino says. “Everything that (Rizzani de Eccher) fought on the ground, we’re now fighting as we erect.”

Also, despite the considerable efforts made by the team to ensure that each segment is designed and constructed to perfection, sometimes erection doesn’t proceed as anticipated, says Gardino. “So some of those [falsework] towers have more load on them than we’ve anticipated, and other towers have less.

“The model says it’s going to do one thing, and sometimes [the arch] is stiffer,” he continues. “Sometimes you’re loading the towers more than anticipated. Not only do you have the impacts of geometry, but then you have the impacts of the loading on the falsework towers as well.”

The Fountain Bridge is designed to be an icon for the city of Miami.  
Rendering courtesy Florida Dept. of Transportation

An example of this issue occurred with the precast segment erection for Arch 5.

“We erected Arch 5 to where we thought we were in great shape, but the loading on the towers was not where we thought it was going to be,” Gardino says. “So now something that we thought we’d be in and out of in a month might take us two months, because the arches just weren’t acting like we thought they were going to.”

Looking ahead to completion of The Fountain Bridge, architect MacDonald sees a bright future. “It’s so unique, there’s nothing like it in the world,” he says. “So it’s really going to be a dynamite thing.”