Omega Morgan bridge move to save up to US$10 million

By Alex Dahm07 January 2013

As part of a replacement project in the USA, moving, rigging and transport specialist Omega Morgan will slide a road bridge crossing a river in what it claims as one of longest bridge moves attempted.

The Sellwood Bridge, at 1,972 feet long, 75 feet high and, 28 feet wide (600 x 23 x 8.5 metres), is one of the state of Oregon’s busiest bridges, carrying some 30,000 vehicles a day. On 19 January 2013 a Pacific Northwest-based Omega Morgan crew will slide the entire 87 year old structure, in one piece and on a radius, into a new position over the Willamette River. It will then become a temporary route from 24 January while a new US$307.5 million bridge is built in the original location.

“We are really pleased to be involved in this highly important, complex and exciting project,” said John McCalla, Omega Morgan CEO and president. It is complicated by the fact that this will not be a straight-across move. The east end will be moved by 33 feet (10 m) while the west end will be moved 66 feet (30 m). The new bridge will open in 2016.

Omega Morgan and general contractor Slayden/Sundt Joint Venture have used this detour bridge method on other projects. “Omega Morgan has moved bridges weighing upwards of eight million pounds (3,629 tonnes), but this one does offer some additional challenges,” McCalla said.

Ralph DiCaprio, Omega Morgan chief engineer, said the company welcomes the challenge. “This is why we like what we do. There’s something different on every project.”

Devising a strategy to move the bridge in one piece helped Omega Morgan win the contract after showing that it will save time, money and duplication of effort, the company said. Other proposals suggested expensive and redundant structural features and extensive staging. DiCaprio created a plan to slide the aging Sellwood Bridge on skid gear to the north of the existing bridge and then mount it on new piers that have been built in the river. This will then become the “shoofly” or detour, while construction begins on the new bridge.

Larry Gescher, construction manager at Slayden/Sundt Joint Venture, said advantages of the shoofly process, include: a saving in the range of $5 to $10 million over other methods proposed; the new bridge can be built entirely in one phase, it saves up to a year in construction time; the temporary detour structure will be as strong as, if not stronger, than the existing Sellwood Bridge (including seismically.); there is no need for redundant structural features on the new bridge and this method allows for a sleeker design. A major safety benefit is that drivers will travel over the temporary bridge so they will be separated from construction workers, who will have a safer work environment.

Temporary approach spans have been installed at the west and east ends of the relocated bridge to link Highway 43 in southwest Portland to S.E. Tacoma St. These will remain in place throughout construction of the new bridge.

The Sellwood was Portland’s first fixed-span bridge, which means it was the first in Portland that did not have a draw or swing span. In 1960 the bridge was extensively repaired to prevent it from collapsing after settling issues caused cracked concrete.

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