72nd Ave BNR Overpass Seismic Retrofit

The City of Delta is conducting a seismic retrofit upgrade on the 72 Avenue BNR Overpass in North Delta as a part of the roadway improvements. This bridge, constructed in 1985, spans the Burlington Northern and Santa Fe Railroad (BNR). Spannovation, working on behalf of the prime consultant MJL Engineering Ltd., is responsible for the preliminary and detailed designs for the seismic retrofit along with specifications and a class “A” construction cost estimate.

The bridge, which is 90m long and has 4 lanes, is a continuous structure with three spans arranged in the following order: 26m, 36m, and 30m. The superstructure comprises 8 precast concrete I-girders that support a cast-in-place concrete deck. The west abutment rests on concrete-filled steel pipe piles, while the east abutment is supported by a spread footing. The piers feature a cap beam supported by three columns. The foundation of the west pier consists of concrete-filled steel piles, while the east pier rests on a spread footing.

The retrofit strategy involves seat widening, installing shear keys at the abutments, and concrete shear keys at Pier No.1, all designed for collapse prevention and load path continuity. At Pier No.2, cap beam strengthening, and concrete shear keys ensure load path continuity and overstrength capacity protection. Both piers receive fibre wrapping; Pier No.1 fully wrapped for overstrength shear capacity and spiral anchorage confinement, while Pier No.2 has it applied over plastic hinge zones to enhance ductility. Pier No.2's plastic hinge zones' fibre wrapping design is aimed at providing equivalent confinement to the as-built spiral design. The shear key design at the abutments is developed for elastic demands based on the 6th generation seismic hazard.