By Kevin Wilcox
Engineers, contractors, and fabricators teamed up to replace a crucial section of I-85 in just six weeks.
Traffic is moving again on I-85 after the bridge replacement, which took extraordinary effort on the part of the design and construction team. Courtesy of the Georgia Department of Transportation
May 23, 2017—On March 30, at the heart of evening rush hour in Atlanta, thick black smoke began to billow from beneath a span of an elevated section of the northbound part of Interstate 85. The fire, which investigators say was set intentionally, burned for nearly two hours, fueled by high-density polyethylene pipes in a state-owned storage area below.
The intense heat and prolonged duration of the fire caused the tensioning strands in the massive prestressed-concrete beams to relax, and the span, known as span 30, collapsed. And so, within two hours and without warning, one of the largest metropolitan areas in the United States—with nearly 6 million residents—lost a vital, 10-lane highway.
"It was a little bit of disbelief, frankly," says Marc Mastronardi, P.E., M.ASCE, the director of construction for the Georgia Department of Transportation (GDOT), recalling how he felt looking over the smoldering rubble that Thursday night. But his disbelief very quickly turned to resolve. What followed was nothing short of a heroic effort by engineers, fabricators, and contractors to reopen I-85 as quickly as possible.
The stakes were exceptionally high. This section of I-85 carries about 250,000 motorists per day. The primary detour for commuters needing to continue through or past the city—I-285—was already congested and immediately experienced an increase in traffic of almost 20 percent. The local routes fared even worse, says Meg Pirkle, P.E., GDOT's chief engineer. "The local streets and even the state routes right around this collapse were very, very taxed," she says. "Atlanta did not develop around a grid system, so there were no good alternates for the traffic in that area." Traffic volume on Peachtree Road, an important north-south corridor in the city, increased by about 40 percent, and traffic on nearby Cheshire Bridge Road more than doubled.
The intense fire delaminated concrete on the beams and columns of the spans. Demolition took just one week. Courtesy of the Georgia Department of Transportation
Many hours elapsed before state bridge inspectors could safely access the surrounding spans. When they did, the news was not good. Using hammers to sound the concrete of the columns, caps, and superstructure, they found serious delamination and spalling issues on the five spans that surrounded span 30—two northbound and three southbound.
"The prestressed beams had delamination issues along the bottom flange," explains Bill DuVall, P.E., the GDOT's state bridge engineer. "As they would tap on [the concrete], it would actually fall off. We knew at that point we had real issues with the adjacent spans."
Governor Nathan Deal declared a state of emergency for Fulton County, which enabled the Federal Highway Administration officials who were on the scene that Thursday night to authorize the use of a negotiated contract for the project. This obviated the need to develop a full set of plans before advertising the project and then awarding a contract. "That was absolutely a key to jump-starting the reconstruction," says Mastronardi.
Pirkle says that this freedom essentially turned the recovery effort into a design/build project, "where our state bridge engineer was the project manager. As our bridge office completed elements of the design, they were immediately passed off to the contractor or the beam fabricator."
In fact, DuVall was on the phone with fabricators of prestressed beams the night of the collapse while he was standing in front of the wreckage. Those spans on I-85 employ type V beams as defined by the American Association of State Highway and Transportation Officials (AASHTO), which were modified for the particular features of the site.
"This was a pretty complicated area, as far as the bridge goes, because we had Piedmont Road cut through at a steep skew," DuVall says. "In order to do the framing of the beams adjacent to Piedmont Road, we had these trapezoidal spans. Every span of the six spans had different beam spacings and different span lengths."
A massive crane placed beams for the new spans. Crews worked 24 hours a day, 7 days a week to complete the project as soon as possible. Courtesy of the Georgia Department of Transportation
DuVall learned that using the original beam type would probably delay the project, as such beams are less common now than they were in 1984, when the spans were built. Instead, DuVall and his team chose to use the 63. in. bulb-tee beam developed by AASHTO, which has the same depth but a more efficient design.
"But that also meant we had to go design every single beam," DuVall explains. That amounted to 61 different beams, some more difficult to fabricate than others. Engineers working on the replacement spans had a valuable resource at their disposal, however. The original plans for the spans had been placed in a digital archive in 1996.
"Having these plans was a huge benefit," DuVall says. "We were able to mimic a good portion of the plan. But we were also able to utilize it for the new portions we designed. We did allow some … changes. We allowed the use of steel diaphragms to speed construction. We typically use concrete. But we had details available for the steel diaphragms, and I know the contractor really appreciated that."
GDOT hired C.W. Matthews Contracting Company, Inc., based in Marietta, Georgia, as the contractor on the project. D.H. Griffen Companies, headquartered in Greensboro, North Carolina, was the subcontractor that led the demolition phase, which took just one week. The demolition team, working with GDOT engineers, carefully removed the sacrificial pins at the ends of the beams and ensured that everything was removed without damaging any elements that were to remain.
"It was amazing that within a week of the event the site was cleaned up," DuVall says. "It transitioned right into construction activity really well."
Because some of the six spans were more conventional, C.W. Mathews focused its attention on those areas first, working with the fabricator to manage a schedule for delivery. The construction team essentially designed a precise construction schedule that worked backwards through the project from the easiest elements to the most difficult.
"They deserve an incredible amount of credit," Mastronardi says, noting that the compressed schedule and the round-the clock, seven-day-a-week workload required especially precise assignments. "That's almost hourly to be looking at, 'Where do I go next? If there's a hurdle, how do I clear it?'"
The team was able to reuse the original foundations. With the aid of hand hammers, the contractor's crew members carefully removed concrete from the columns until they reached beyond any fire damage to the main steel reinforcement running from the top to the footings. Afterward, additional reinforcing and new concrete were added to rebuild the columns.
The team originally set a goal of June 15 to reopen the bridge, which included a number of days that were expected to be lost to weather. A key hurdle was the delivery of the 61 custom-fabricated beams. The fabricator used two factories to fulfill the order, and GDOT authorized deliveries of the oversized loads around the clock, complete with an escort by the Georgia State Patrol.
Mindful that having the highway out of commission during the busy Memorial Day weekend would create massive headaches both for motorists and for public safety personnel, GDOT issued the contract with a stepped incentive program for early delivery.
"As an agency, we do that rather selectively," Mastronardi says. In this case, however, GDOT was armed with economic data indicating that the missing link in I-85 was costing just the motorists using the I-285 detour a staggering $550,000 to $850,000 a day in lost time, extra fuel, and inconvenience. That didn't include the lost income of small businesses in the area, which were suffering. "No one wanted to travel through there to go do anything," Pirkle says.
"We knew that, if we were done by Memorial Day weekend, that was a big win," Mastronardi says. So, the contract included a $1.5-million lump sum incentive for the project to be completed on or before May 25. If the project was completed by May 21, $2 million would be awarded. Beyond that, there was a $200,000 bonus for each day earlier than May 21 to a maximum of $3.1 million.
The spans opened ahead of even that optimistic schedule, on May 13, buoyed by exceptional weather and the expeditious action of DuVall and his team of engineers in deciding on which beams to use and then designing them quickly. "The biggest challenge from the very beginning was the beams," Pirkle says. "When Bill decided that he was going to redesign them and then get the plans to the contractor by the next day, that is really what set the ball rolling to get the project done early."
At a May 18 ceremony, Elaine L. Chao, the secretary of the U.S. Department of Transportation, joined Governor Deal, Russell McMurry, GDOT's commissioner, and other state officials in celebrating the project's completion. "I am proud of the response and collaboration shown by all throughout the entirety of this rebuild," Deal said at the event.
"We were very aware of the urgency," McMurry said. "I have never been more proud of the Georgia Department of Transportation and the tireless efforts of our employees."