Tuesday, March 16, 2010

Engineering Feat for Giant Cranes to Pass Under Golden Gate and Bay Bridges

Transporting three $10 million, 1,500 ton cranes from Asia to Oakland to pass under the Golden Gate and Bay Bridges has been a major engineering feat involving months of planning.

The cranes arrived in San Francisco Bay this morning aboard a special barge - see previous blog.

'It's a lot of work. It takes a whole team to be able to move these cranes from Asia,' said Robert Bernado, Manager of Media and Public Relations for the Port of Oakland.

With an emphasis on safety, 'God forbid it actually touches the bridges - what would happen to the morning commute....!'

With expert engineering, however, the cranes passed under the Golden Gate Bridge with a clearance of 14 ft and under the Bay Bridge with a gap of 9 ft.

The difference reflects the variables that the engineers have had to factor in, and tides are one of them. The barge sailed on a low tide, but the bridges themselves are another variable as they contract or expand by a few feet depending on weather conditions, explained Robert Bernado.

One of the Port of Oakland's engineers spent the weekend at Point Reyes, Marin County, working with engineers from the shipping company, Evergreen Marine Corporation. 'They were clearly monitoring tide tables,' he said.

The cranes fold down at the apex and the barge itself can lower or raise its height by taking in or off-loading water in a technique called de-ballasting.

This cargo is called Super-Post Panamax cranes, one of the newest generation of cranes, but already their predecessors, the Post Panamax cranes, could load and unload containers from a ship too wide for the Panama Canal. These 'Supers' have a 120 ton load capacity and can lift up to four 20 ft or two 40 ft long containers, confirmed Robert Bernado.

As the Zhen Hua 15 sailed under the Bay Bridge, it turned at right angles to head for the port. Watching the giant cranes unload is fascinating, said Robert. The barge lightens its weight to rise to the level of the dock and the cranes, each on four wheels, roll off.

'Without naming names, there have been ports where the cranes have rolled onto the terminal and right into the water!' he said.

The three cranes now bring the total of Super-Post Panamax cranes at the port to 22. The port is the third busiest in California and the fifth busiest in the US handling, with fluctuations, around two million 20 ft containers per year.

pics by Chris

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