Bridging the Columbia River: Past, Present, and Future
By Luke Carothers
Spanning over 3,500-feet across the Columbia River where it draws a border between Oregon and Washington, the bridge that now carries I-5 between Vancouver in Washington state and Portland in Oregon first opened to traffic in 1917. This important piece of infrastructure was incorporated into the newly built Interstate-5, which ran roughly parallel to the West Coast of the United States. Then a single bridge carrying two-way traffic, the structure was expanded in 1958 when a second twin bridge was built directly adjacent to the original structure. With the twin bridge structure, each bridge was opened to one- way traffic–northbound traffic being run over the 1917 structure and southbound over the 1958 structure. As a part of the Interstate Highway System, this transportation corridor expanded in importance and the bridge crossing the Columbia River between Oregon and Washington has come to represent a vital piece of infrastructure when speaking about the continued growth, economic success, and happiness of communities throughout the region. In existence for over a century, the I-5 bridge over the Columbia River has become outdated, leading to a number of significant problems that negatively impact those living in surrounding communities. The lift bridge design is so outdated that there are less than 20 still in service throughout the United States. Most significantly, perhaps, is the I-5 Bridge’s vulnerability to seismic activity. The current structure is a lift bridge that rests on timber piles driven into a silty river, which makes it incredibly prone to serious structural damage in the event of an earthquake. The most likely seismic threat to the structure is the Cascadia Subduction Zone, which is roughly 70 years overdue for a significant movement.
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csengineermag.com
October 2023
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