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Sellwood Bridge's new foundation takes shape

'THE BIG POUR'


by: DAVID F. ASHTON - The east side landing site is brilliantly illuminated as this Sellwood Bridge Big Pour goes on into the night. After months of building the concrete forms, installing rebar, and laying in cooling pipes, the new Sellwood Bridge Project took a giant step forward during a 22-hour period starting on January 10 that the County called “The Big Pour” of the eastside footing.

This footing needs to be sturdy, commented the project’s spokesman Mike Pullen, as he led an evening tour of the worksite during the continuous pour. “This will support the steel arch span where it touches down.”

The hoppers of two large pumping units were kept filled with freshly-made concrete by a never-ending caravan of ready-mix trucks, queueing up on S.E. Spokane Street.

Contractor Slayden Sundt’s “Joint Venture General Structure Superintendent” Josh Smith was watching it take place.

“This is, truly, a big pour,” Smith told THE BEE. “It’s our first mass concrete pour on this job. We’re running about 18 workers per shift, for three shifts, because the footing needs to be finished in one continuous pour.”

The footing goes down 18 feet from the top layer of rebar – and is fitted with many layers of rebar, Smith pointed out. “The footing contains a half-million pounds of rebar. When we’re done with the pour, it will have taken 1,860 yards of concrete.”

Smith pointed out boxes protruding from the top layer of rebar, into which the workers were pumping seemingly endless amounts of concrete. “These are actually hoppers that guide the fluid concrete into the form.”

Dropping concrete from too great a height causes the finer particles in the mix to splash away from the larger, heavier particles, we learned. In addition, the force of the mix striking the reinforcing steel may shift bars out of position.

“So, the maximum drop height or ‘allowable free-fall’ is five feet,” Smith said.

Dozens of sets of flexible gray plastic tubes entered the form from the south side, and exited from the north side carrying recirculated cool water, strategically spread out through the form. Concrete doesn’t “dry”; a chemical reaction causes it to “cure”, which produces an exothermic reaction. That is, heat is liberated during both the setting and hardening process of the concrete.

“Even though it’s chilly out here at the worksite this evening, the concrete needs to be kept at a uniform temperature to make sure it has the maximum strength when it sets,” Pullen commented.

This isn’t the biggest ‘Big Pour’ the bridge will see, either,” Pullen observed. “The west side footing will be even larger, because the landing is wider on that side.

February 14 bridge closure

After project managers proposed closing the Sellwood Bridge for construction work during the week leading up to Valentine’s Day, Sellwood-area businesses objected to the timing.

“We read all of their feedback, and we spoke with the County and got the start date of the bridge closure pushed back to midnight on Friday, February 14th,” Pullen said.

The bridge is now scheduled to close at midnight on Friday, February 14 and reopen by midnight on Wednesday, February 19. So the bridge will be closed on five days, including two normal commute days (February 18 - 19), same as the original plan.