The youngest bridge of the three bridge crossings across False Creek will require rehabilitation work to help the structure withstand a moderately-powerful earthquake, according to a new City of Vancouver staff report.
Vancouver City Council is expected to approve a contract with Associated Engineering Ltd. worth up to $5.5 million for services that involve supplying a design for the bridge’s rehabilitation, as well as an increase of $425,000 to the budget for the bridge’s seismic assessment.
The bridge was constructed in 1985, just in time for the Expo ’86 World’s Fair, but the municipal government says lessons learned from recent major earthquakes elsewhere in the world — including Northridge, Kobe, and Christchurch — have led to advances in structural response understandings and revisions to design codes.
This includes a performance-based approach to design instead of strength-based design, a review and change to the earthquake return period, increased soil liquefaction potential, increased understanding of how to predict the interaction between the soil and the bridge, and improved detailing requirements to both steel and concrete structures.
“Although the bridge has been constructed fairly recently, our understanding of seismic performance of structures has changed since the 1980s,” reads the report.
“From the various studies it has become clear that the bridge does not meet the current seismic code requirements and, given the increased seismic hazard and potential for soil liquefaction, the bridge is not expected to perform well. After a moderate-level earthquake, the bridge would likely need to be closed and require replacement.”
A moderate-level earthquake is deemed as a seismic event with a magnitude of approximately between 5.0 and 6.0, but its actual impact on structures depends on the location of the epicentre and depth.
The city says the 870-metre-long bridge sees an average of about 55,000 vehicles per day, and a complete replacement would currently cost $400 million. A new bike lane was installed on the bridge’s southbound direction last summer.
The other two bridges across False Creek are far older; the 1932-built Burrard Street Bridge saw seismic upgrades earlier this decade, and the 1954-built Granville Street Bridge will see its share of seismic upgrades over the coming years as a part of a number of bridge improvements.