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Multnomah County is approaching completion of a project to replace four 8-foot-diameter Rall wheels on the Broadway Bridge in downtown Portland.

To allow crews to carry out related work, the bridge will close to all traffic the nights of April 2 and 3, the county announced. The Rall wheels, which allow the drawbridge section of the Broadway Bridge to open and close, were replaced last year after more than 100 continuous years of service.

The bridge will close to all traffic on Monday, after the last streetcar crossing of the day takes place at 11 p.m., according to county spokesman Mike Pullen. It will reopen at 5 a.m. on Tuesday. During the closure, a survey of drawbridge parts will be carried out and a shim will be installed on one of the tracks supporting the Rall wheels. The survey cannot be carried out with traffic present because of the bridge vibration it causes.

Then the bridge will again close to all traffic on Tuesday at 11 p.m., but then reopen periodically following temporary closures of up to 20 minutes. It will reopen without more disruptions at 5 a.m. on Wednesday.

Pullen said TriMet will detour several bus routes that normally use the Broadway Bridge south to the Steel Bridge.

Rall wheel replacement work by Hamilton Construction began in July 2017 and will finish this spring. The wheels and double-leaf drawbridge mechanism are rare. Using four large steel wheels, large weights are rolled back from the center, allowing larger weights to lift the bridge’s two center spans. The old cast wheels weighed some 56,000 pounds each, while new solid steel wheels forged by Portland’s Peninsula Iron Works carry more heft at 88,000 pounds apiece. The mechanism allows ships of any height to pass through the bridge. Peninsula Iron Works is the only facility of its type on the West Coast, and its handiwork can be found in all five of Portland’s movable bridges.

Complicating the work, each Rall wheel supports the entire weight of the opening spans, some 2,250 tons each. Because of this, work on the wheels could take place only when the spans were closed. Replacing the wheels required about three months for each side.

More information about the project is available at .