Although Jan. 20 was a federal holiday, some Birmingham, Ala., commuters may well have elected to take a drive downtown. That’s because for the first time in almost a year, I-59/20 through the city’s central business district was open to traffic, nearly ending a marathon $700-million effort to replace the 6,600-ft-long corridor’s deteriorating viaduct with safer, precast segmented structures designed to better serve the city’s steadily growing volume of vehicles.

While the public’s willingness to tolerate travel inconveniences in return for expedited infrastructure renewal has been tested many times elsewhere in the U.S., the Alabama Dept. of Transportation’s decision to close a key freeway through the heart of the state’s largest city for at least a year was not taken lightly.

What was certain, says DeJarvis Leonard, ALDOT regional engineer, was a need for action, as the original half-century-old structures were showing their age and the effects of handling a daily load of more than 160,000 vehicles—twice their design capacity. Leonard says the deck was in “horrible condition,” its surface riddled with pop-outs.

“We were spending about $1 million a year on replacing those areas,” he says.

Ruling out redecking and other conventional construction approaches as insufficient to address the viaduct’s deficiencies, ALDOT saw that a full replacement strategy capitalizing on segmented construction could help offset the added cost and inconveniences of a closure by facilitating a faster erection process. And because the existing bridges had been perceived by many Birmingham citizens over the years as a barrier separating the city’s neighborhoods, a more aesthetically pleasing replacement structure would provide longer open spaces between piers that could be repurposed into parks and other public areas.

ALDOT and its design consultant Volkert mapped out a three-phase plan to bring the I-59/20 corridor up to date using design-bid-build project delivery. The first phase, constructed by Brasfield & Gorrie, reconstructed several nearby thoroughfares to handle the burden of additional traffic; in the second phase, Granite Construction Co. rebuilt I-59/20’s nearby interchange with I-65.

“The interchange project also included some new ramps separate from the bridges that improved access into downtown during the closure,” adds Adam Patterson, Volkert project manager.

For the third and final phase, ALDOT tapped contractor Johnson Brothers Corp. of Roanoke, Texas, in June 2017, with Volkert also providing construction engineering and inspection services. Though the project used design-bid-build delivery, the nearly two-year-long planning phase proved highly collaborative.

“We evaluated any design change that might help us get in and get out just that much faster,” says Johnson Brothers project manager Mike Brown, citing examples such as lengthening the 34- to 47-ft-wide, double-barrel precast segments from 10 ft to an average of 12 ft, 7 in. That reduced the total number of segments by 600, to just over 2,300. All component fabrication would take place at a temporary batch plant located near Birmingham’s airport, approximately two miles from the project site.

Meanwhile, ALDOT worked with Birmingham transportation officials to prepare for what it hoped would be a maximum 14-month shutdown of I-59/20 through downtown beginning at the end of January 2019. Along with identifying and designating the most efficient detour routes and retiming signals, the agency worked with multiple Birmingham agencies to conduct an extensive public outreach program to raise awareness and answer questions. A multi-mode media blitz in the six months leading up to the start of construction likewise sought to minimize motorist surprises and frustrations.

“Anyone who didn’t know bridges were coming down must not have been in Birmingham,” Leonard says.

Take-Down Strategy

With the last barriers installed at the corridor’s ends and access ramps, demolition of the old elevated structures got underway. Rainy winter weather, typically the bane of contractors, played a positive role in suppressing dust. Except for a few ramps that were imploded, heavy machinery and hydraulic attachments were sufficient to complete the demolition work in little more than half of that phase’s allotted 90 days. All concrete and metals were recycled locally.

While the original design for the bridge’s columns called for drilled shafts and H-piles, a planning-stage design change switched approximately 40 percent of the foundations to modular micropiles, which were less complicated to build in the dense urban setting. At locations where the drilled shafts did not conflict with existing foundations, a low-overhead pile-driving rig allowed installation to get underway well before the bridges were scheduled to close.

“We had about 70 percent of the foundations installed before starting demolition,” he says.

Another time-saving innovation—precasting more than 160 columns and 41 curved pier caps—also helped save valuable time. Johnson Brothers could erect an entire 20- to 30-ft-tall four-pier bent in just two days, a fraction of the time Brown says is typically required for cast-in-place columns and caps.

“You can imagine the resources that it would have taken to do that, compared with the three column forms and four cap forms we used,” he adds.

Rather than use an overhead gantry for installation, the contractor utilized shoring to install the superstructure segments, believed to be the first application in the U.S. Brown says the idea was inspired by a similar project in the Middle East. To guard against differential soil settlement, crane pads supported the 12-ft by 12-ft shoring towers, while Liebeherr 330-ton 1300 cranes equipped with hydraulically powered segment-lifting devices oriented the segments into place.

As the project team found its stride with the installation process, construction accelerated with as many as 400 segments installed each month. But although the demolition work had provided a clear construction site, the constrained corridor nevertheless afforded limited elbow room. Workers had to be continually mindful of nearby adjacent office buildings, hotels and public facilities such as the Birmingham Museum of Art. With as many as 30 cranes on site, Brown says, “Planning crane moves took months.”

And as might be expected in a dense urban setting, the project team also had to sidestep what Brown calls “an astounding amount” of underground utilities, including a 115-kV oil-filled transmission line. Two separately owned rail crossings also presented coordination challenges. The strategy for minimizing closure times involved erecting 160-ft-long portal beams on falsework, then sliding the segments across and into place for gluing and post-tensioning.

About the only hiccup in the project team’s plan was the discovery of 24 bridge segments that failed to meet ALDOT’s specifications for ride smoothness. Johnson Brothers chose to recast the segments rather than attempt to grind the surfaces back.

“We discovered the problem early enough, and it really didn’t affect the schedule at all,” Brown says.

Indeed, ALDOT was able to begin 2020 by heralding the reopening of the I-59/20 corridor two months earlier than scheduled, an accomplishment that earned Johnson Brothers a $15-million early completion bonus. In addition to restoring access to downtown and improving safety with 10-ft shoulders, the design of the new structures eliminates a longstanding merge problem with the addition of a 4,000-ft-long auxiliary lane between the I-65 interchange and the Red Mountain Expressway.

Shifting Gears

As Johnson Brothers spends the next few months finishing its work with the new bridges’ associated streetscape, lighting and erosion control work, attention now turns to newly opened areas below. Plans are being finalized for the 10-block, 31-acre project—to be called CityWalk BHAM—with a proposed mix of amenities that includes trails, skate and dog parks, play areas for children, recreational fields and other features. ALDOT will bid CityWalk as a separate contract this summer.

While Birmingham motorists may marvel at the rapid replacement of the I-59/20 corridor, Leonard admits to being just a little surprised by the achievement. He recalls engineering consultant studies that predicted that new bridges could be built in nine months.

“We weren’t sure whether to believe them, but it turned out to be true,” he says, adding that subtracting the demolition phase, the new bridges were actually erected in just six months.

“It shows what you can do when you have a good plan,” he says, “and a good team approach.”