Construction wrapped up in January 2016 on a seismic retrofit project for bridges along the Interstate 5 corridor in the Portland metropolitan area. Five bridges between Portland’s South Waterfront district and the Tualatin River comprised the initial package of work.
Why a Seismic Retrofit Program?
Most bridges in Oregon built prior to 1990, the year modern seismic design specifications for bridges were developed, are vulnerable to a major earthquake. The March 11, 2011 earthquake in Japan provided a stark reminder of the importance of building structures so they can survive a major seismic event. Many scientists believe the Pacific Northwest is overdue for the same type of seismic event that struck the Japanese coast (a subduction zone or "megathrust" earthquake) where sustained shaking of the ground can cause extensive damage to buildings and infrastructure. The 2011 Japanese earthquake was a magnitude 9.0. The last megathrust earthquake in this region was the Cascadia earthquake in 1700, which had a magnitude 8.7 to 9.2. According to research conducted by the Oregon Department of Geology and Mineral Industries, there is a 40 percent chance a similar powerful earthquake will occur along the Oregon coast sometime in the next 50 years.
In response to these findings, ODOT conducted a seismic vulnerability study of the state highway bridges to assess the risks to Oregon’s only north-south interstate highway. The result? Only a small portion of I-5 would remain passable if the state suffered a substantial seismic event; most of the older bridges would either collapse or experience severe damage and become impassable without major and very costly repair work.
ODOT’s initiative to retrofit the state’s older bridges to meet modern seismic specifications will ensure I-5 would remain open in the event Oregon experiences a powerful earthquake. The sites selected to begin receiving improvements represent just the first phase of an expected multi-phase program to improve the seismic rating on bridges throughout the region.
WORK IS COMPLETE ON ALL FIVE BRIDGES SHOWN BELOW
Project Locations, schedule and traffic impacts
(click on each project location below for a fact sheet specific to the bridge)
I-5 over SW Hood Avenue (South Waterfront, City of Portland)
Traffic alert: Work began on this bridge in March 2014 and was complete in May 2015. The construction required a 24-hour single lane closure on SW Hood Avenue under the I-5 bridge for approximately 12 months.
Read a frequently asked questions document and the fact sheet for more details about the bridge work and the detour.
OR 99W (SW Barbur Avenue) over I-5 (Portland/Tigard city limits)
Work began on this bridge late April 2015 and was complete in January 2016. See the attacher flier for more information. Work will be complete in fall 2015.
I-5 over Portland & Western Railroad (unincorporated Washington County)
Work began on this bridge in Sept. 2014 and was complete in fall 2015. No traffic impacts are expected during construction.
I-5 over SW Lower Boones Ferry Road (Tualatin/Tigard city limits)
Traffic alert: Work began on this bridge in March 2014 and was complete in January 2016. More details are in the fact sheet.
Full nighttime closures of Lower Boones Ferry under I-5 are complete. No more closures are expected.
I-5 over Tualatin River (Tualatin/unincorporated Washington County)
Traffic alert: Work on this bridge began May 2014 and was complete in October 2014. Boaters in the Tualatin River had safe passage mid-channel during construction. Read more project details in the fact sheet.
Under current conditions, older bridges on the I-5 corridor would not be able to withstand a major seismic event. The seismic retrofit work – strengthening the piers, pilings and bridge abutments – brings those structures up to modern seismic design specifications, which will make them better able to withstand a powerful earthquake.
The project increases the safety of Oregon drivers using the state-maintained transportation system. It also helps ensure that a major transportation and freight route remains accessible to speed vital supplies and services to areas needing assistance.
The seismic retrofit work maximizes taxpayers’ dollars by increasing the lifecycle of the existing network of bridges, thereby lowering the costs required to replace an entire freeway system following a major earthquake.
To receive project updates electronically or for more information, contact:
Lili Boicourt, Community Affairs Coordinator