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.
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