Westshore Terminals Overpass
Faced with progressive deterioration of their 40-year-old, single-lane Bailey bridge, Westshore Terminals retained Associated Engineering to design its modern replacement. Working closely with a geotechnical consultant, Associated Engineering’s designers determined that the most economical approach to bridging on the marine fill site was a series of lightweight simple spans on single-column piers and low-bearing pressure footings, occupying the same footprint as the existing bridge. Four 30 metre spans were selected to cross the two rail tracks and access roads, with the earthfill approaches retained with mechanically stabilized earth walls. The selected scheme was chosen for its ability to accommodate future predicted ground deformations.
A major consideration was accommodating the 1 in 2475-year earthquake ground motions for the Class F marine-fill site. Drawing on its experience with cost-effective design of base-isolated bridges, Associated Engineering was able to solve this stringent design challenge by installing ‘link decks’ between the spans to create a continuous deck diaphragm and ‘tuning’ the isolators to suit the flexibility of each individual substructure component. The isolators selected are simple elastomeric bearings vulcanized to plates bolted to both superstructure and substructure.
All details were carefully selected for use by industrial traffic, including off-road vehicles and to avoid the accumulation of coal dust, which is prevalent at Westshore’s busy coal terminal. With trains occupying the rail tracks most of the time, track occupations for removal of the Bailey Bridge and erection of the new superstructure are limited. As a result, the new superstructure comprises steel plate girders and full-depth precast deck panels to speed installation and limit field work. Durability is enhanced by designing-in protection from deck run-off for components beneath the expansion joints at each abutment.
Construction occurred in the summer of 2017 to minimize site occupation and the resulting impact on coal terminal operations. The new structure provides two-lane operation and full load capacity.