The Fast Life

Feb. 1, 2006

The New Orleans area celebrated as the final two lanes (westbound structure) of the 5.4-mile I-10 Bridge over Lake Pontchartrain opened earlier than anticipated on Jan. 6. Nicknamed “Twin Spans,” the 42-year-old, I-10 eastbound and westbound bridges were extensively damaged and rendered impassible by Hurricane Katrina on Aug. 29.

The New Orleans area celebrated as the final two lanes (westbound structure) of the 5.4-mile I-10 Bridge over Lake Pontchartrain opened earlier than anticipated on Jan. 6. Nicknamed “Twin Spans,” the 42-year-old, I-10 eastbound and westbound bridges were extensively damaged and rendered impassible by Hurricane Katrina on Aug. 29.

This portion of I-10 serves as the primary transportation corridor in the continued rebuilding effort of New Orleans. The twin spans carry a majority of the commerce activity, residents and emergency services daily into New Orleans to restore the historic city that has served such a vital role in the settlement and shaping of our nation as we know it today. The project also stands as a model of the states’ urgent commitment to the rebuilding of Louisiana. To reinforce this commitment, Gov. Kathleen Blanco and Louisiana Department of Transportation and Development (LaDOTD) Secretary Johnny Bradberry cut through the extensive red tape to formalize a proposal to repair the damaged structure. This was best illustrated by the LaDOTD’s ability to prepare and advertise the contract on Sept. 7 and award the contract to the low bidder on Sept. 9, just nine days after the full effects of Hurricane Katrina. The low bidder, Boh Bros. Construction LLC of New Orleans, was awarded the $30.9 million emergency repair contract, with HNTB Corp. of Baton Rouge serving as a subconsultant in providing engineering and construction services. Material and equipment were mobilized over the weekend and work began on Monday, Sept. 12.

The team had 45 days to open the eastbound structure to two-way traffic (120 concurrent days to open the westbound structure). For each day of delay in opening the eastbound structure, the team would be assessed $75,000 in damages. Everyone knew the operation would be a 24-hour, seven-day-a-week task given the vast number of damaged spans. The bridge itself consists of twin structures of 436 spans each. Each span is roughly 65 ft in length and 45 ft 6 in. in width (weighing 260 tons). The structure is typically founded upon three 54-in.-diam. cylinder pile bents.

Pockets of punishment

To fully comprehend the damage incurred and repairs required, one needs to understand how the dynamics and sequence of events of Katrina impacted the twin spans bridge. As Katrina moved to the north and east of the site, the storm surge entered Lake Pontchartrain from the east while the wind and wave action came from the west-northwest. At this location, I-10 runs predominantly north-south. With the low members of the bridge at approximately 8.5 ft above mean high water and a structure depth of approximately 4.5 ft, the storm waters rose to depths that totally encapsulated the precast units. As a result, air pockets formed beneath the bridge and buoyed the spans. This phenomenon combined with the wind/wave action to cause a general shifting of all spans to the east. The structure experienced repeated damage to the girders, with the only lateral restraint provided by the increased height of the bearing pedestals on the bent caps. As a result, 38 spans on the eastbound structure fell into the water while 20 spans on the westbound structure fell. On the eastbound structure, 171 spans were misaligned, while 303 were misaligned on the westbound structure. Because of the extensive misalignment on the westbound structure, girder damage and more than three miles of damaged barrier railing, it was decided that the eastbound structure would be repaired first.

Relocate to reconstruct

While the construction task at hand was indeed a challenge, Hurricane Katrina also had significantly affected the methodology and work force dedicated to performing the repair work. The team assembled to complete the work was composed of mostly Louisiana residents. Its purpose was to demonstrate that the state’s resources could meet the challenge even in the face of personal adversity. Boh Bros., being headquartered in New Orleans, lost its offices and temporarily worked out of various offices including those of HNTB in Baton Rouge during the proposal preparation. Nearly every member of the team was personally affected. While many lost their homes or received major structural damage to their homes, the remainder used their homes to house those who were less fortunate. Even the basic necessities were absent on site—food, gas, ice, water, power, communication and more—for an extended period of time. Many of these items had to be brought in daily to sustain the work force. A large majority of the subcontractors lived on site in generator-driven trailers as a consequence.

A new way of working

To meet the contractual demands, the entire team employed a tireless effort that was best demonstrated by the around-the-clock work schedule using two 12-hour shifts. Crews worked at night with the use of generator-powered lights on the bridge and barges. The ability to work also was controlled by the lake conditions. Due to the great expanse of Lake Pontchartrain and its shallow waters (generally 10 to 15 ft) weather conditions easily generated 3- to 4-ft swells, which greatly added to the challenge of realigning the spans and concrete debris removal.

Coincidental to the initial task of repairing the eastbound structure, the team also was faced with the effects of Hurricane Rita, which affected construction activities for four days. Despite these many challenges, the eastbound structure was repaired in 28 working days, 17 days ahead of the 45-day schedule. In a similar manner, the westbound structure also was opened ahead of the 120-day schedule of Jan. 14, 2006.

The project required a high degree of innovation, collaboration and trust among everyone. The entire process was very unconventional. There was very little time for ordering materials, and resources were scarce in the area due to damages nearly all local suppliers experienced.

The repair process was to cannibalize the good spans from the westbound bridge and move them to the eastbound bridge to yield a complete structure. The remaining spans on the westbound bridge were then arranged to yield two continuous gaps of missing spans—one each on the north and south end of the bridge. In these locations, temporary, steel truss Acrow bridges were installed on the existing bents to bridge these gaps.

A secondary goal was to maximize the Boh Bros. materials, equipment and personnel on site and at the nearby equipment yard. HNTB prepared the repair procedures, reviewed within a four-hour window and executed within hours.

The repairs themselves were very unconventional and specific to the availability of materials. For example, nearly all the girders experienced damage due to the attachment details of the steel rocker bearings. If the damage was between 20% and 45%, conventional 25-ton screw jacks, available on the Internet, were installed to support the girders. Some of the more extensive repairs are summarized below:

  • The lateral storm surge resulted in the misalignment of 473 of the project’s 872 spans (displacements of up to 7 ft). The spans were realigned using two procedures. The first entailed the use of two steerable hydraulic trailers that could sit atop the barges to lift the 260-ton span and move it back in place to within a 1?4 in. of its original location. The second method involved a jack and slide system where shallow waters limited the use of the barge. In this procedure, Teflon plates were placed beneath the span and the entire span jacked up from below. Simultaneously, hydraulic rams were positioned on each end of the span and braced against opposing curbs of the adjacent spans to jack the span into place;
  • Used 506 25-ton screw jacks to support the moderately damaged girders;
  • Used reinforced neoprene bearings to replace 320 rocker bearings;
  • Custom-cut radius Teflon-like material at Boh’s equipment yard to replace 638 damaged or missing bronze bearing plates;
  • Used 96 saddles (tubular supports attached with PT bars to the exterior of the cap) to support the more heavily damaged girders;
  • Used 11 “helper bents” to support girders with extensive damage. Helper bents consisted of a needle beam supported on 4-24-in. pipe piles driven outside the footprint of the existing bridge;
  • Installed four new pipe pile bents to replace two destroyed bents;
  • More than three miles of temporary barrier replaced the barrier railing on the westbound bridge that was totally destroyed;
  • Epoxy was injected into approximately 2,000 ft of cracks in the deck, bents and girders and grout repairs of more than 4,000 sq ft of curb and deck;
  • Placed 64 spans (approximately 4,200 ft) of temporary Acrow steel truss bridge (700 Series);
  • Modified 68 bents to accept the Acrow Bridge;
  • Moved nearly 100 260-ton spans to re-establish the eastbound roadway and contiguous openings for the Acrow Bridge;
  • Installed a pile jacket to encapsulate a 54-in. hollow cylinder pile damaged by fallen spans;
  • Installed metal plate curbing to replace isolated sections of the damaged barrier railing;
  • Added striping and signing to more than 12 miles of roadway and bridge structure to accommodate all phases of the repair contract; and
  • Removed and demolished all “leaning spans.” Rubble in place all totally submerged fallen spans.

The final phase of the repair contract has started with a three-year inspection program of the temporary Acrow structure. This interim three-year period will accommodate the time required to build a new six-lane replacement structure east of the current structure. The project has been appropriately named the “Road to Recovery” and is a testament to the commitment of the Boh Bros. team, HNTB Corp. and LaDOTD personnel. As the community has stated, the bridge is truly the “twin spans” once again.

About The Author: Gowins is department manager for structures with HNTB Corp., Baton Rouge, La.

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