The Interstate 5 Bridge trunnion replacement project won’t begin in earnest until September, but preliminary work is already underway at the site, including the Tuesday morning arrival of a barge carrying the new sheaves, trunnion and other replacement components for the bridge’s lift system.
The northbound span of the bridge will close to all traffic Sept. 12-20 while contractors swap out the old parts for the new ones and perform other repairs. The primary impetus for the $13 million project is a crack in the existing trunnion at the top of the bridge’s south tower. The trunnion is like an axle between the two sheave wheels that move the bridge cables.
The crack was discovered in 1999 and has been continuously monitored since then, according to Oregon Department of Transportation spokesperson Don Hamilton. It began to spread more quickly in the past two years, which means the trunnion needs to be replaced to ensure the long-term health of the bridge, he said.
During that same time frame, Oregon and Washington have embarked on a renewed effort to build a replacement bridge for Interstate 5, but any potential project is still years away and the outcome of the current discussions is anything but certain. In the meantime, the trunnion can’t wait any longer, Hamilton said.
“Our obligation at this stage of the game is to keep this bridge functioning as safely as possible,” Hamilton said. “That’s what this project is about.”
The northbound span is the original bridge opened in 1917 (the southbound span was added in 1958), so replacement parts aren’t readily available. The new trunnion and sheaves were custom-built by a fabricator in Alabama, Hamilton said.
The new parts were shipped by truck and arrived last month at a marine yard in Portland near the St. Johns Bridge, Hamilton said, and from there they were transferred to the barge. The barge departed Tuesday morning and traveled down the Willamette River and then up the Columbia River to the bridge.
The barge is equipped with a construction crane, so its arrival required a bridge lift to reach the northbound span. The barge will remain anchored in the river to the east of the bridge for the next several weeks leading up to the start of the project, Hamilton said.
Preparation work will continue at the site during the lead-up to the closure, including the construction of a tower crane next to the south tower later in August.
Additional projects are also currently underway along I-5 through Vancouver, including the installation of a bus-only lane on the shoulder of I-5 south and a new active-traffic management system with message signs for drivers and variable speed limit signs for individual lanes. Both projects are targeted to wrap up before the closure and are expected to help alleviate some of the congestion.