Seismic Vulnerability of the Alaskan Way Viaduct: WSDOT Typical Unit

An engineering team from the University of Washington (UW) evaluated the seismic vulnerability of the Alaskan Way Viaduct, located in Seattle, Washington. This report presents the evaluation of a typical three-bay unit that was designed by WSDOT. The evaluation team performed response-spectrum analyses and nonlinear analyses for both fixed-base and pinned-base conditions. The team considered a widely used soft-soil spectrum and worst-case, site-specific spectra. Wherever possible, the UW team evaluated the vulnerability to each failure node following two or three procedures, including those proposed by the Applied Technology Council (1983) and Priestley, Seible, and Chai (1992).

The evaluation team found that the vulnerability of the Alaskan Way Viaduct exceeds that of bridges built to current standards. The vulnerability is a result of a combination of two factors: (1) the ground motion is likely to strongly excite the viaduct; and (2) many of the WSDOT unit's structural components are likely to behave in a brittle manner. The following deficiencies were identified as the most critical.

  • The first-story column-reinforcement splices are too short, they have too little confinement reinforcement, and they are located in regions likely to experience large ductility demands.
  • The column/beam joints have inadequate confinement reinforcement, and during strong ground motions, they could experience a diagonal-tension failure.
  • The shear strength of the first-story columns is marginal.
  • If the first-story columns develop their flexural capacity during an earthquake, the pile-supported footings could fail in shear.
Publication Date: 
Thursday, June 1, 1995
Publication Number: 
WA-RD 363.1
Last modified: 
10/12/2016 - 15:41
Marc O. Eberhard, Jaime De La Colina, Stanley Ryter.
Washington State Transportation Center (TRAC)
Number of Pages: 
Brittleness, Columns, Deficiencies, Earthquake resistant structures, Failure, Flexural strength, Joints (Engineering), Nonlinear systems, Seismicity, Shear strength, Splicing, Viaducts.