Alexandra Bridge Deck Rehabilitation and Seismic Retrofit
Location
Fraser Canyon, British Columbia
Expertise
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The 481 metre long Alexandra Bridge originally built in the 1960’s crosses the Fraser River via a 256 metre steel arch main span and steel girder approach spans.
In 2009, Associated Engineering carried out a detailed condition and renewal options assessment and recommended rehabilitation of the bridge. Following this, we carried out the rehabilitation design of the structure.
We first conducted a detailed bridge inspection including a visual inspection of all accessible components using a bridge inspection truck for access below deck level. The inspection identified that the steel approach span girders and arch steelwork were in fair condition with minor corrosion; however, the concrete deck had significantly cracking and delamination.
Following the investigation of renewal options and life cycle cost analysis, we developed a renewal scheme that incorporated a partial-depth concrete deck overlay to address concrete deterioration and widen the roadway deck to 12 metres. Our assessment indicated that continuous deck diaphragm action was necessary to eliminate seismic vulnerabilities. This involved re-articulation of the approach spans and installing link decks across the breather joints near the arch crown.
Client
Government of British Columbia
Awards
BC MOTI Deputy Minister’s Consulting Engineering Awards, Award of Excellence
Project Highlights
481
metres long
256
metre span
We carried out a non-linear buckling analysis of the steel arches to confirm their inherent ability to support the heavier applied loading. A key feature of the deck widening scheme was modifying the previously lightly-loaded fascia girders to support traffic loads, which required new girder seats at the short spandrel columns. In the approach spans, the deck was selectively made composite with the girder top flanges using shear studs. This required girder strengthening for shear and moment at select locations. We added value to the scheme by utilizing spare structural capacity to increase the width of the roadway and improve vehicle containment. We also provided construction inspection and engineering services for the construction and post-construction phases.
In 2019, the project received an Award of Excellence at the 2019 Deputy Minister’s Consulting Engineers Awards.
