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Eastern approach to new Sellwood Bridge takes shape

by: DAVID F. ASHTON - This driver deftly maneuvers his long load through the tight intersection of S.E. 17th Avenue and Tacoma Street. Even though it was well-publicized in advance, and despite flashing message boards on S.E. Tacoma Street, many motorists seemed surprised – even shocked – to find barricades blocking off the Sellwood Bridge to vehicular traffic at 7 pm on Tuesday evening, May 13.

A half hour later, the first of several trucks carrying very long pre-stressed concrete beams for the bridge’s east-side approach arrived in Sellwood from Knife River Construction in Harrisburg, near Eugene.

Each semi rig, hauling one girder, had a relatively easy drive up Interstate 5 and Interstate 205 before exiting on the Milwaukee Expressway (Highway 224), and turning north on S.E. 17th Avenue.

Although is a relatively small intersection, the truck drivers made the left-hand turn from S.E. 17th to westbound Tacoma Street look easy. One of the drivers told THE BEE that the extended trailer units had originally been purchased by Wilhelm Trucking for transporting long, heavy, and fragile 140-foot wind turbine blades. “And they are also ideally-suited for moving 110-foot-long concrete beams,” the driver said.

The driver described an automatic mechanism, where the front pivot point of the truck actuates hydraulic pistons that caused the rear trailer truck wheels to turn slightly in the opposite direction, allowing them to make relatively tight turns with a long load.

As the sun set, three girders were waiting in line at the east foot of the Sellwood Bridge, ready to be hoisted into place the next morning.

With the bridge closed to traffic, and clear weather, May 14 it was an ideal day to start placing the 27 girders at the east end approach.

When he previously spoke with THE BEE about this phase of the project, Multnomah County’s spokesman for the project, Mike Pullen, had indicated the bridge would simply be closed for brief, intermittent periods.

“However, when the project planners considered the number of trucks and beams planned, they later decided that a full closure would provide a better work flow,” Pullen explained. “And, it gave drivers consistency, rather than guessing if the bridge would be open or closed during the work period.”

Each girder was custom-manufactured to fit in each of the “slots” spanning from Bent 6 at the Willamette River’s bank, to the eastern abutment.

“Pre-cast girders are built in forms that include steel strands,” Pullen described. “The strands are pre-stressed [stretched out] before the concrete is poured into the form. After the concrete cures, the strands are slowly released causing them to compress the concrete, adding strength.”

The largest girder installed during the 72-hour work marathon was 109 feet, 7 ¼ inches long…2 feet wide…5 feet, 3 inches tall…and weighed 75,080 pounds.

Lifting each girder off its trailer and setting it in place required two construction cranes.

One crane looked huge, while the other, to the west of it, looked spindly and small.

“Actually, the smaller crane is capable of lifting twice the load of the big one,” remarked Project Sponsor (the project’s “CEO”) Ted Aadland. “We chose that particular crane because it is small enough to retract and reposition under the girders, and then fully retract and be able to be driven out of our of the worksite.”

We found it like watching an “industrial ballet”, as the crane operators deftly plucked each 37+ ton girder off its trailer and gently-but-precisely set each in place on thick, black pads positioned on top of the bents.

“Those are bearing pads, made of a very dense rubber, Aadland informed THE BEE. “It prevents having concrete-to-concrete contact. They’ve a little bit of ‘give’, providing shock absorption, so the concrete doesn’t fracture.”

Pointing east from our vantage point on the bridge, Aadland said the girders and pads would eventually be totally encased in concrete at Bent 5. “But at Bent 6, this is a ‘floating’ end. Concrete ‘boxes’ will be cast over the rebar that’s sticking up from the base of the bent. These will keep the girders from shifting under a heavy load – or during a seismic event.”

Like clockwork, over the following days, one rig after another rolled up to the worksite with a girder just as crews finished placing the last giant beam.

By 1 pm on Friday, May 16, the Sellwood Bridge was again reopened – ahead of schedule. “The combination of good, dry weather and a quick ‘learning curve’ for placing the girders sped up the work, and that was responsible for the early opening,” Pullen said.