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Storm surges lift bridges off their supports

News

CONTRACTORS IN New Orleans are to cannibalise parts of the badly damaged twin deck Interstate 10 (I-10) motorway bridge as part of a $30.9M, 45 day temporary repair plan.

Louisiana's Transportation Department said that undamaged spans from the hardest hit of the two decks would be used to plug gaps in its twin.

Much of the 42 year old I-10 bridge lies just 2.8m above mean high water mark.

It lost 64 of its 866 spans in the massive storm surge which swept across Lake Pontchartrain during Hurricane Katrina.

The 8.6km crossing comprises a westbound bridge and a parallel eastbound structure.

Each comprises 433, 21.6m long prestressed concrete monolithic spans carried by concrete piers, plus two 30m composite steel plate girder spans and one 60m composite steel plate girder which carry the deck up 21m above a shipping lane.

The eastbound deck lost 38 of its concrete spans, while another 170 were misaligned.

The westbound deck lost 26 of its spans, while another 303 were misaligned.

Contractor Boh Bros is carrying out the emergency work. It will reinstate one of the decks using cannibalised sections. As NCEI went to press engineers were still determining which of the decks sustained the most damage.

Boh Bros will also move undamaged spans from the most damaged structure to one end of the crossing before plugging the gaps with portable temporary steel spans.

The contractor will maintain the temporary spans for up to three years. In the long term the bridge will be rebuilt as a higher level structure.

At Biloxi the Highway 90 crossing of Lake St Louis lost more than 50 spans, again to a storm surge.

Both structures are multi span viaducts made up of concrete deck sections bolted on to cross beams, supported by piers.

As NCEI went to press most of the highway networks in isiana and neighbouring Mississippi and Alabama had reopened. The exceptions were I-10 and Highway 90.

A low lying 60km section of Highway 90 hugging the coast west of Biloxi was also shut.

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