Nearly five years after Hurricane Katrina, affected communities continue to rebuild in the aftermath of one of the worst natural disasters in U.S. history. The Louisiana Department of Transportation is just one of the many agencies working to repair the damage caused by the hurricane.
In August 2005, the Twin Span Bridge across Lake Pontchartrain sustained serious damage from the storm surge. The Louisiana Department of Transportation, along with private-sector agencies, is working on the new bridges to restore transportation on Interstate 10. Together, the repair of these bridges make up the largest public works project in the history of Louisiana.
Work on the $800 million project began in August 2006. The Louisiana Department of Transportation is administering the project. Project activities are being coordinated with the Federal Highway Administration. Boh Bros. Construction Company in New Orleans is building the level portion and the approaches for the new bridge. The 80-foot high rise section is being constructed by the joint venture Traylor/Kiewit/Massman. Volkert Construction Services will provide construction engineering and inspection services in support of the Louisiana Department of Transportation’s efforts.
The new Twin Span Bridge will consist of two parallel structures built adjacent to the current bridge. Each bridge is approximately 5.5 miles long and includes expanded capacity and added safety measures.
“The new bridges include three lanes in each direction and 12-foot shoulders on both sides of each bridge so that people can stop safely on either side,” Project Manager Arthur D’Andrea says. Even before Hurricane Katrina, the bridge faced problems, including corrosion, D’Andrea explains. This made for a potentially dangerous situation. “The idea was to retire the worse bridge as soon as possible,” he says.
Twice a week, crews had to weld, repair and close lanes to keep traffic flowing on both bridges. It cost the state close to $200,000 a month to keep the old bridges going during construction of the new bridge.
“We had to combine the best parts of the old bridges in order to make one good bridge to get traffic going,” D’Andrea says. “The maintenance to keep traffic going wasn’t cheap.”
The old bridges were retired in April 2010. East and westbound drivers now cross Lake Pontchartrain entirely on the new bridge. Traffic on either side of the bridges share eastbound approaches until the old structure can be demolished and the westbound approaches constructed. The project is expected to be completed in 2011.
Searching for Resources
The Louisiana Department of Transportation faced some difficulties getting started on replacing the Twin Span Bridges, especially considering the slate of reconstruction projects all competing for the same resources in the months following the hurricane.
“Trying to rebuild a new structure in post-Hurricane Katrina era was hard,” D’Andrea recalls. “Although the engineering design was led by an in-house team, circumstances had everyone scrambling for the same limited resources.
“We feared we couldn’t afford to replace the bridges,” D’Andrea continues. “We asked Congress for the money.”
Force of Nature
The new Twin Span Bridge is designed to be taller, stronger and more hurricane-resistant than the previous bridge. The Louisiana Department of Transportation wanted to design a bridge to hold up to the force of a hurricane. Since the agency had little guidance on how to accomplish this task, it looked at bridge design for extreme events in Florida and Japan, D’Andrea says. “We worked with experts to come up with guidelines,” he adds.
The new rigorous standards for designing a bridge to withstand hurricane wind and wave action resulted in bridges that are better able to resist lateral forces that would otherwise shake a structure to pieces. The details in some ways resemble those built in earthquake zones, according to the agency.
Wind and wave action from Hurricane Katrina battered the old bridge, knocking out more than 400 concrete deck spans out of alignment. Another 58 concrete spans toppled into Lake Pontchartrain in the wake of the hurricane. Each concrete deck weighs more than 200 tons.
The record-breaking storm surge caused by Hurricane Katrina also lifted many of the 309-ton concrete spans off its piers and broke the steel bolts that anchored them in place. Some of the spans toppled into the lake while others were seriously misaligned.
The eastbound bridge lost 38 spans and another 172 were knocked out of alignment. On the westbound bridge, 20 spans were destroyed and another 265 were misaligned.
The new bridge is 21 feet higher than the old bridge – 30 feet vs. 9 feet. To keep the bridge sturdier, the bridge design includes shear keys, reinforced steel and concrete tie-ins between the bridge decks and caps.
Using pre-cast caps and girders helps improve the bridge’s performance by preventing misalignment and toppling due to storm surge, according to the agency. Having these elements already cast has made for a much easier construction process than pouring the concrete on-site. D’Andrea says the use of pre-cast has been a lifesaver for the Twin Span project so far.
“To pour concrete in the lake, even though it’s shallow, is difficult,” D’Andrea says. “It’s a big-time savings to minimize concrete pouring by barging in pre-cast elements.”