Hawthorne Bridge: History, Construction & Facts

Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

The Hawthorne Bridge is just one of many in Portland. What makes it so special? In this lesson, we'll check out the history and significance of this structure, and see what it means to Portland today.

The Hawthorne Bridge

There are many reasons to visit Portland: the culture, the music, the food, and of course, the bridges. While not all outsiders are aware of this, Portland is exceedingly proud of its many bridges, and for good reasons. One that stands out, is the Hawthorne Bridge. Spanning the Willamette River, it's the busiest bicycle and transit bridge in all of Oregon. Impressed? What if we told you it's the oldest highway bridge in Portland? Maybe we should just jump right to its biggest claim to fame: oldest working vertical lift bridge in the United States. Yeah, that's pretty impressive.

The Hawthorne Bridge
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Design

At its most basic, the Hawthorne Bridge is a vertical lift bridge, which simply means that its main span can be elevated vertically into the air. Why would you need to do this? The elevation of the main span increases the clearance enough to let boats pass underneath, without forcing engineers to build the entire bridge at that height, which would require some extremely steep approaches for vehicles to climb. In order to raise this span, 450-ton counterweights are strung through the 165-foot tall bridge towers. Lowering the counterweights sets a series of pulleys and cables into action that lift the elevating span. Considering the heavy boat traffic of the Willamette River, this happens about 200 times per month.

Let's take a step back, however, and look at the bridge as a whole. While only one span can be lifted into the air, the entire bridge is actually composed of 6 total spans. Five of these are stationary, but combine to give the structure an impressive length of 1,382 feet. The load-bearing decks of these spans are supported by steel-frame trusses, which also makes this a truss bridge. If we want to get really technical, then the diagonal tension bars, the vertical compression bars, and a curved top chord that changes slope more than five times identify these as Parker through-truss spans. Tell that to someone in Portland. They'll be very impressed.

The Hawthorne Bridge contains six steel-truss spans
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History

Of course, what good is it to be able to identify truss types if you don't know the bridge's history? Crossing the Willamette River has been a major priority since Portland was founded, and the Hawthorne Bridge comes from a long line of predecessors. The first structure in that spot was a wooden structure completed in 1891. It was poorly built however, and was replaced in 1900 by another wooden bridge. Unfortunately, a fire in 1902 jumped from the city to the bridge, destroying it. Portland was again faced with replacing the structure, but this time they wanted to build something that could withstand the test of time.

1909 drawing of the proposed Hawthorne Bridge
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Rather than wood, the city commissioned a steel bridge to cross the Willamette River. A Kansas City firm called Waddell and Harrington was hired to build the structure, and construction began in 1909. The Hawthorne Bridge quickly became a testing ground for the newest and most advanced ideas in vertical-lift bridge technology, and several innovations were realized here. For one, the engineers found a way to ease the stress on the counterweight cables, transferring the pressure to basic operating cables that were much easier and cheaper to replace. The Hawthorne Bridge was also the first electric-motor vertical-lift bridge, leading to innovations in the placement of things like the bridge-operator's room. While this may not seem like that big of a deal, the success of the Hawthorne Bridge's functional design set the standard for future bridges built around the world.

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