Lane Lefort/ENR Construction has started on an $803-million replacement bridge over Lake Pontchartrain.

In designing a replacement, $803-million, 100-year, Interstate 10, twin-span bridge across Lake Pontchartrain, Louisiana highway officials say they are raising the bar on bridge designs to increase their resistance to hurricanes.

Construction has begun on the new bridge and Louisiana Dept. of Transportation and Development officials say it will be much higher and stronger than the one it replaces. New design elements include girder restraining keys and reinforced attachments that address lessons  from Hurricane Katrina. The Westbound side is scheduled for completion in 2009 and the eastbound side in 2011.

Katrina’s 30-ft storm surge on Aug. 29, 2005, tore apart the 42-year-old crossing, bashing the deck off 58 spans and misaligning 473 others. “An event like that prods national attention and awareness of the need for [new] design criteria,” says Hossein Ghara, LaDOTD bridge design administrator. Engineers are using the damage to guide them.

Kris Wascomb

“This is one sturdy bridge,” says GJ Schexnayder, the bridge’s project manager for Boh Bros. Construction Co. LLC, New Orleans. Boh won the $379-million contract to build the two, 4.5-mile-long, 60-ft wide, low-level runs. A joint venture of Traylor Bros. Inc., Evansville, Ind.; Kiewit Southern Co., Atlanta; and Massman Construction Co., Kansas City, Mo., is apparent low bidder, at $166.7 million, for raised portions that include a pair of 200-ft-wide by 80-ft-high spans across a shipping channel. The award of the federally funded contract is pending federal approval, says Brendan Rush, spokesman for  LaDOTD.  The balance of the cost is for design, environmental studies, administration and demolition, Rush says. Volkert Construction Services Inc., New Orleans, is performing construction engineering and inspection services on both contracts.

The new bridge is 300 ft south of the old one. At 30-ft-high, the low deck will be 21 ft higher than the original. “If a storm surge comes that is big enough and tall enough to knock this bridge down, there is no way the hur-ricane protection system in New Orleans will survive,” says Schexnayder, who was on the Boh job to perform emergency repairs on the old bridges after Katrina.

Ghara says the American Association of State Highway Transportation Officials does not have bridge design standards for hurricane wind and wave resistance, so LaDOTD developed its own. “One of the things detrimental about the existing bridge is the elevation. If it had been about 10 ft higher, it most likely would not have toppled,” Ghara says.

The new bridge meets AASHTO’s ship impact standards. “That means it incorporates larger foundations, more redundant members (pilings) and more reinforcement to engage the piles with the caps, making them more resilient to lateral impact,” Ghara says. The bridge also will be built with higher-performance, high-strength (10,000-psi) concrete that is more resistant to saltwater corrosion and wind and water loads, he adds.

Lower-level connections are strong.  “In the area where we had to transition to a lower elevation to meet the roadway at the two ends, we had to make a very strong connection of the superstructure to the substructure,” Ghara says.

"The beams are connected by means of dowels placed at angles to the cap to resist uplift."

Angelle Bergeron/ENR Schexnayder is Boh Bros.’ project manager.

Shear keys have been added to restrain the girders against lateral displacement. "The girders sit on top of the riser pads, and the shear keys -- 1 ft 8 in. by 1 ft blocks -- sit on side of the riser pads, blocking the girder into place," Schexnayder says. "They form a little pocket."

Boh will construct the low-level portion using 36-in. square precast concrete pilings barged in from Gulf Coast Pre-Stress of Pass Christian, Miss. On Dec. 5, Boh began driving production piles ranging in length from 85 ft to 170 ft A series of 135-ft, bulb T girders will transition up to the elevated portion, which will be topped with a 650-ft continuous steel plate girder over the navigational channel.

The two contracts have overlapping deadlines to ensure the westbound bridge opens to traffic in October 2009 and the eastbound opens August 2011. Boh's contract includes a $15,000-per-day bonus incentive, to a maximum of $4.5 million, for early completion. "That means we would have to finish by December 2008," Schexnayder says.