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Transit New Zealand is eager to learn the cause of the United States motorway bridge disaster, but says it is confident in the inspection procedures for its 4000 highway bridges.
Network operations general manager Roly Frost said his agency spent about $30 million a year maintaining its bridges, including $5 million for Auckland's main transport lifeline across Waitemata Harbour.
"With $5 million you can give quite a lot of tender love and care," he assured the Weekend Herald.
The US Government has ordered inspections of more than 70,000 bridges after an eight-lane structure collapsed into the Mississippi River in Minneapolis on Thursday, killing at least four people and injuring 79.
Federal officials have disclosed that it was rated "structurally deficient" in 1990 and 2005, and claim the state of Minnesota ignored warnings by relying on patchwork repairs.
Mr Frost said Transit understood work was being undertaken on the bridge when it failed, but it had yet to find out what that involved. He said it was of a truss-steel design of similar configuration to the central part of the Auckland Harbour Bridge, which was built in 1959, and to which "box-girder" clip-on lanes were added 10 years later.
Truss-steel structures, which included criss-crossing networks of horizontal supports between the main arches, were generally robust and frequent inspections of the harbour bridge had disclosed no problems.
Although the clip-ons posed a greater challenge, mainly from having to repair fatigue cracks, these were under almost daily surveillance.
But he acknowledged that just over 300 bridges were below a seismic design standard required to withstand earthquakes likely to occur once in 2500 years, and would take at least a decade to bring up to scratch through an annual funding allocation of around $5 million.
