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.