Preparation to jack the arch ribs apart

From ODOT-

The construction team is completing necessary preparations to jack the arch ribs apart, which lifts them off their falsework and forces each rib to support its own weight.



As part of the preparation, crews meticulously calibrate the equipment using a process that we described earlier this year. Additionally, crews removed the formwork from the spandrel columns, which extend from the arches to the deck, and installed cradles cast into the arch ribs to hold the hydraulic cylinder that powers the jack.

On the left, you can see a couple of spandrel columns that crews exposed by removing the formwork. One column still has the formwork in place.

Finally, using a crane, workers will hoist the large hydraulic ram jacks and place them into the cradles.



Once the jacking starts next week, crews will survey and mark the columns at each stage to evaluate how the movement is affecting the columns and abutments. On day one, crews will jack the arch to an 80 percent threshold and then engineers will determine if there was any pressure shift in an up-close inspection. The next day, crews will jack the arch ribs to 100 percent threshold, and will check them again.



Once the arch ribs are separated and lifted, crews can pour the concrete closure that completes each arch and allows them to stand on their own.

Crews make last substantial pours on new northbound bridge arches

From ODOT-

Our team recently poured the top sections of the southernmost arch for the new northbound Whilamut Passage Bridge. These top portions are called crown arch rib sections and they will soon be joined together to complete the graceful arch that will support the deck to carry freeway traffic.

Crews poured approximately 100-foot segments on each side of the arch apex, starting at the peak and working down each side of the curved arch ribs to the previously-poured lower sections. As we’ve described before, the rebar framework of the bridge arches is surrounded by wooden falsework and formwork, creating a form that allows fresh concrete to cure in the desired shape and size.

Poured in a series, you can see the result of a previous arch pour in this photo. Notice that lower portions of the formwork were removed, but the crown arch rib section formwork remains intact.

What's next? The construction team will jack apart the arch sections located on the north bank next week, using large hydraulic ram jacks. Just after the New Year, crews will repeat the jacking process on teh recently poured arch sections of the southermost arch. Each arch will require a closure pour after being jacked apart completing the final arch shape. Our goal is to complete the first closure pour on the northernmost arch before Christmas.



Other than the minimal but critical closure pours, these crown arch rib sections are the last arch pours on this project the new northbound bridge is definitely taking shape.

Arch construction - a closer look

From ODOT-

This fall, we will complete the arches for the new Interstate 5 northbound bridge, following the same construction process used to build the southbound bridge arches.

One of the final steps is to raise each arch section about two to three inches off the falsework by pushing the arches apart with four large 965-ton hydraulic jacks. The jacks are positioned in the gap at the top of the arch and simultaneously separate and lift each so crews can pour the concrete closure that completes each arch and allows them to stand on their own. .

Similar to a jack you would use to lift your car, a single hydraulic pump applies pressure to each of the four jack rams, which separate the arches. Each ram has its own pressure gauge. Close calibration ensures that the rams and the gauges provide uniform and accurate information so equal pressure is applied and the arches aren’t damaged.

The calibration process pressurizes the rams up to 95 percent of their maximum capacity while individual gauge readings are recorded. Once the calibration is complete, crews must set up the system identically when moving the arch sections, using the same gauge and ram combinations they used during testing.  

Only a few facilities on the West Coast can test such large hydraulic rams. The University of Washington, in conjunction with the subcontractor team from Precision Hydraulic, will calibrate the jacks over a two-week period this month.

The university provides written certification of the calibration along with a copy of the data collected during the tests to help ensure accuracy during this critical process.

From ODOT- The Arch Falsework comes down

Our contractor, Hamilton Construction, has spent more than nine months building the two graceful arched spans that will support the new southbound Interstate 5 bridge. As you travel past the construction project, you may have noticed the arches nearing completion.

Starting last April, crews built falsework to form the arches. They started by erecting steel supports on the work bridge and welding them into place. On top of the steel supports, the crews built a wooden deck and forms that outlined the curve of the arches. Inside the arch forms, they built a “skeleton” of reinforcing steel bars that gives each arch both strength and flexibility. Finally, crews filled the forms with concrete that protects the reinforcing steel and adds to overall strength.

Now that the arches can stand on their own, we have started dismantling the wooden forms and steel support system. Most all of the material will be saved and stored near the site and reused to build the arches for the northbound I-5 bridge.

With all the falsework now removed in span 2, the weight of the arches is fully supported on large concrete shafts that were constructed deep in the ground on either bank and in the middle of the river.

The graceful lines of the river crossing can now be seen.





Here are the arches under construction, with falsework in place.


Here are the span 2 arches standing free of falsework.

Arch Ribs photo story part 3 of 4

From ODOT-
This is part three of our series on the creation of the deck arches that will support the new Willamette River Bridge, and will be beautiful, graceful structures in their own right.

First, we saw how the foundations are built to provide support for the arches. Then, we learned how the arches will connect, and saw the initial formation of the arch frames. This week, we will see how wooden frames and concrete pours shape the columns and arch frams.

In the foreground of this picture are the vertical support spandrels, which were built using the same method as the arch ribes. Based on the rebar-cage frame, crews built wooden forms to define the shape of the columns, filled them with poured concrete in sections and once the concrete is cured, removed the forms to reveal the finished columns.

On top of the steel falsework support frame, crews built a wooden frame to provide a safe platform for the workers and a steady foundation for the massive rebar cages that form the backbone of the arch ribs.

Rebar cages provide support for the concrete, which is poured in sections. The strength of the steel physically ties each section together, making a single, continueous arch out of individually constructed segments. The reinforing steel used on the Willamette River Bridge is the largest diametere available and weighs about 13 pounds per foot. With such a heavy frame, once the arch ribs are poured they will tip the scales at more than 11 million pounds.

In this photo, ironworkers prepare the rebar cages for the wooden forms that surround them and give shape to the poured concrete arch sections.

Next: framing and pouring the arch ribs.