Infrastructure over a period of time degrades and needs replacement. This what happened to the 87 year old Sellwood Bridge in Portland, Oregon. The bridge had developed cracks along the beams making travel unsafe. The city of Portland as a precautionary step reduced the weight of the bridge from 32 tons to 10 tons banning entry of heavy vehicles. After nine years, the city of Portland had engaged a team of engineers to move the 3,400 ton bridge in one piece rather than demolishing it. Engineers used hydraulic jacks to raise the bridge’s span off the old concrete piers. They placed the horizontal jacks in place and pushed the span across steel translation beams where it came to rest on a separate set of piers. By this the city has saved between 5 and 10 million dollars and had reduced the construction time of the new bridge by up to a year. Now the Sellwood Bridge is thrown open for traffic. Kristian Foden-Vencil who has been following the work said the bridge did not groan or creak but slid in place while placing it on a separate set of piers. Banging or screeching must have led to breaking or twisting of steel.
The bridge was checked with lasers and strain-gages to confirm that it remained straigth. Later with GPS to make sure it is in the right place, People were asked to commute slowly all over the bridge to make sure that no rivets popped or steel cracked. Engineers re-calculated all the loads and stresses of the bridge before clearing the project. The temporary new pilings of the bridge that stands on are up to current earthquake standards. The bridge is very smooth and more solid. The speed limit has been dropped from 30 miles per hour to 25 miles per hour because a couple of turns have been incorporated on the ramps. The bridge is now safe for heavy vehicle traffic.