Structural Movement and Damage to the Alaskan Way Viaduct Due to the Nisqually Earthquake

摘要

This paper addresses the effects of the February 28, 2001 Nisqually Earthquake on the Alaskan Way Viaduct located on the Seattle Waterfront, approximately 35 miles from the epicenter. Seismic ground motions at the Viaduct will be summarized from the seismic monitoring stations. Supplemental physical evidence from buildings and bridges in the vicinity provide a basis for characterizing the seismic ground motion. Preliminary findings indicate that the most significant ground movement was transverse to the bridge centerline, corresponding to seismic shear wave propagation from the epicenter, with a gravitational coefficient (g) of approximately 0.16. There is also some evidence of localized soil subsidence in the vicinity of the adjacent seawall attributable to the earthquake. Established elastic movement and permanent deformation of the Viaduct as a consequence of the seismic ground motions is discussed. Inspection findings document information establishing conclusions presented, with information gathered from historical bridge records. These inspection findings indicate that the bridge generally moved within elastic limits transverse to the roadway centerline, with some longitudinal movement in portions of the southern end. Inspection findings subsequent to the earthquake provide the basis for discussion of structural damage, and will include structural failure of the Pier 100 East column, and structural distress to Piers 94, 97, 121, 145, and 160 including adjacent crossbeams and longitudinal beams. Other bridge conditions not directly related to the earthquake will be addressed as they affect the seismically induced damage, including settlement of selected foundations A description of how the monitoring programs were developed and how they will be used in the future to determine structural movement is presented. Two methods for recording small structural movement have been implemented. One system is based on surveys with established control points and a second system utilizes "crack monitors" installed on the bridge over selected structurally significant cracks.