Oak Street Bridge seismic retrofit

The 2km long Oak Street Bridge carries Highway 99 between Vancouver and Richmond was built in the late 1950’s. Between 1993 and 2004 the bridge underwent a comprehensive seismic retrofit and rehabilitation. Changes to codes and seismic hazard models since that time have resulted in substantially higher seismic loading requirements. In 2021, BASIS teamed with WSP to undertake a seismic study of the retrofitted bridge for the larger ground motions. A ship impact assessment of the main span over the north arm of the Fraser River was also undertaken.  

Typical span configurations were studied using Response Spectrum Analyses and representative piers were examined using Non-linear Pushover Analyses. Liquefaction of the foundation soils was evaluated, and lateral spreading ground displacements were estimated.  

The capacity of the retrofit piers was compared to these higher demands. There are almost 100 piers supporting the bridge and they had all had some seismic retrofits in the previous program. The new results were extrapolated to all the piers and additional retrofits were identified to meet the new requirements. This information provides important input into MOTT planning of future work in the corridor, and for Emergency Response planning.