Rebuilding the I-85 bridge a complex, costly process

GDOT engineers started designing fixes night of the collapse.

Rebuilding a bridge isn’t as simple as snapping together pieces like an oversized Lego set. Building one fast is even more complicated.

Georgia Department of Transportation engineers began designing fixes for 700 feet of the I-85 bridge the night a fire caused a portion of it to collapse and badly damaged other sections.

Marietta contractor C.W. Matthews Co., which will be paid up to $16.5 million to complete the project, started putting together cost estimates that same night. The bridge went up in flames on March 30 after a homeless man allegedly set fire to an upholstered chair, which then ignited several tons of coiled plastic conduit that had been stored underneath.

An indication of how quickly both shops were working: Amounts for each of the 92 line items that make up the budget are written by hand. The Atlanta Journal-Constitution and Channel 2 Action News obtained the contract this past week through a Georgia Open

Records Act request.

“That’s unique; we hadn’t done that in a long time,” C.W. Matthews President Dan Garcia said of the hand-written budget amounts. “Everything happened so quickly, we ended up doing it the old-fashioned way.”

The company’s bid for fixing the bridge was reduced to $11.9 million after a couple of hours of negotiations with the state and Federal Highway Administration, Garcia said. That amount doesn’t include $1.6 million for demolition, or $3.1 million in incentives the company can earn by completing the project early.

The budgeted line items include $3 million for concrete beams; $2.4 million for grading; $1.7 million for fast-curing superstructure concrete; and $1.5 million for traffic control, which includes barricades, signs, fencing and police officers. The federal government is expected to pick up most of the cost of construction.

Major considerations in designing the repairs included the geology of the ground beneath the bridge; the weight of the bridge and vehicles expected to use it; how quickly the concrete cured to specifications needed for a highway bridge; and, perhaps most importantly, how fast the concrete beams could be manufactured.

They even took into account the number of axles on tractor trailers — which distribute the weight of the trucks’ load as they cross the bridge.

“Bridges, by their very nature, are quite complex to design,” said GDOT Construction Director Marc Mastronardi. “The art in it becomes understanding how to take all that information and how to synthesize it.”

The concrete on the columns supporting the bridge cured in 24 hours. The decking is a 72-hour mix. Normally, concrete decking takes 14 days to dry, said Garcia, whose company completed pouring the first of six decks on Wednesday.

“There are costs associated with expediting a project like this,” Garcia said. “You use different chemicals and additives to achieve strength in concrete faster. They are about 35 percent to 40 percent more expensive in a 24-hour mix.

“The beam supplier was critical for us to be able to complete the work more quickly. Standard Concrete (Products) produced all the beams right here in Atlanta, except the ones over Piedmont Road. They began casting the first beams on Monday after the fire.”

Dozens of C.W. Matthews’ employees have worked 24 hours a day to demolish the old bridge and build the new one. Last week, the company had 45 people working at night and 40 during the day. GDOT has four to six inspectors working beside them at all times.

“Our role is the quality assurance piece,” Mastronardi said. “We have staff that are subject-matter experts in bridge construction.”

A stroke of luck that made design and construction easier: The foundation and 13 columns supporting the old bridge were still usable. Mastronardi said that probably saved a month of construction time.

The first step in building the new bridge was shoring up those original columns with more steel and concrete. Next, workers placed reinforced concrete caps over the columns to support 61 concrete beams — each one weighing about 80,000 pounds.

The beams themselves were laid on the caps and tied together for stability. Metal forms are placed to hold the concrete of the bridge deck.

After the decks are poured, they will be tested for smoothness and ground down if necessary. Then they’ll be grooved to prevent them from becoming slick when it rains. Finally, they’ll be striped, and workers will pour the concrete barrier walls on each side of the bridge deck.

GDOT officials said they believe construction will likely be done ahead of schedule before the June 15 deadline.

“Those (barriers) will be a sure sign we’re in the home stretch,” Mastronardi said.

JOHN SPINK / JSPINK@AJC.COM Workers get northbound I-85 prepared for concrete during the repair work this past week for the bridge collapse. The project is expected to be completed by June 15. A fire caused a portion to collapse, resulting in fixes for 700 feet of the roadway.

JOHN SPINK / AJC Piedmont Road, which had been closed since 9 a.m. Tuesday for I-85 bridge repairs, reopened more than one hour ahead of schedule Wednesday. Crews worked overnight to set beams for the new bridge, which officials hope to reopen by June 15.