Date:  Friday, March 19, 2010

Contact: Meghan Soptich Pembroke, WSDOT Communications, 206-440-4704 (Seattle)
Amir Ahmadi, WSDOT Project Engineer, 425-225-8725 (Everett)

Statewide retrofit program strengthens bridges to protect against earthquakes

MOUNTLAKE TERRACE – WSDOT and contractor Granite Northwest, Inc. crews finished retrofitting 19 bridges along I-5 from Tukwila to Lynnwood in early March, nearly six months ahead of schedule. The $12.8 million project was funded primarily by the 2005 gas tax.

“Earthquakes pose a substantial risk to bridges in Washington state,” said Amir Ahmadi, WSDOT project engineer. “Our goal is to bring our bridges up to current seismic standards so we can help keep drivers safe during future earthquakes.”

Crews used three different methods to strengthen the bridges, depending on the individual needs of each bridge. They:

• added concrete blocks between bridge girders to prevent lateral movement
• widened existing concrete caps on top of bridge columns to enhance their stability, and
• reinforced bridge columns by wrapping them in steel jackets.

In all, crews retrofitted six bridges in Tukwila and 13 between Mountlake Terrace and Lynnwood.

Statewide program

WSDOT’s program to strengthen, upgrade and replace bridges vulnerable to earthquakes takes many forms.

Two of our most vulnerable structures are the Alaskan Way Viaduct and the SR 520 floating bridges. Plans to replace these aging Alaskan Way Viaduct and SR 520 bridges are under way: www.wsdot.wa.gov/Projects/Viaduct and www.wsdot.wa.gov/projects/sr520bridge.

Built in the 1950s, the Alaskan Way Viaduct was damaged by the 2001 Nisqually earthquake. Another major earthquake could collapse the seawall and liquefy the soil beneath the viaduct, damaging the structure beyond repair.

Similarly, the SR 520 Evergreen Point and Portage Bay bridges were built in the 1960s, without the benefit of today’s design standards. The hollow columns that support the bridges are seismically vulnerable and could collapse and implode in the event of a major earthquake.

In addition to replacing major structures like the viaduct and SR 520 bridges, WSDOT also has a statewide program to strengthen another 881 bridges to resist earthquakes. The 2005 gas tax dedicated $87 million to retrofit bridges in central Puget Sound to reduce the risk of catastrophic bridge failures during an earthquake. That work, which includes the 19 bridges recently retrofitted on I-5, began in 2007 and will be complete by 2015. As of February 2010, WSDOT had retrofitted 246 bridges in the statewide program.

For more information on the I-5 Central King to South Snohomish Bridges – Seismic Retrofit project, visit: www.wsdot.wa.gov/Projects/I5/KingSnoBridgeRetrofit. For more information on WSDOT’s seismic retrofit program, visit: www.wsdot.wa.gov/Bridge/Reporting/SeismicRetrofitProgram.htm.

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