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Interstate 10 (I-10) over Lake Pontchartrain (Eastbound and Westbound) Near Slidell, Orleans Parrish, Louisiana

Both the east and westbound lanes of the section of Interstate 10 (I-10) that crosses Lake Pontchartrain suffered numerous failures. Near the east end of the westbound bridge, the span was offset only a few inches. As one progresses west, the offset increases to 3-4 feet (see Figure 1). Many sections of the westbound bridge also had gaps where parapet sections had broken off from repeated uplifting and dropping (figure 2). Evidence of this behavior was exhibited by scrapes on the bridge seat, cracking of the concrete deck and some “pounding” of the deck sections against one another and against the pier cap. Water was reported to be over 20 feet high, causing boats and a large amount of debris to be washed up onto the bridge deck.

The concrete bridge was built as a series of simply supported pre-stressed spans, prefabricated off-site for ease of construction. The failure mode is similar to what has been seen after earthquakes, with loss of support at the piers after dynamic loading. In this case, the non-continuous spans were unseated by wave and wind action during the storm (Figures 3 - 6).

Note that the concrete superstructure units have been displaced to the south. This area was west of the hurricane eye and the wind came from the north even though the storm surge came from the south.

Figure 1: Large offset. I-10 Eastbound facing west.

Photo:J. O'Connor (for MCEER)

Figure 2: Broken parapet and debris on the bridge

Photo:J. O'Connor (for MCEER)

Figure 3: Eastbound spans (on left) collapsed into the water.

Photo:J. O'Connor (for MCEER)

Figure 4: Close up view of the eastbound spans collapsed into the water at pier #405.

Photo:J. O'Connor (for MCEER)

Figure 5: This prefabricated superstructure unit shifted off its bearings, but did not fall. Greater seat width as is often provided in seismic regions might have kept more spans from falling into the water.

Photo:J. O'Connor (for MCEER)

Figure 6: Front view of westbound spans collapsed into the water.

Photo:J. O'Connor (for MCEER)

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