As part of the extension of the Vancouver SkyTrain system into Surrey, a new crossing of the Fraser River was required in New Westminster. The north approach spans connect the below-grade section of guideway adjacent to Columbia Street and the cable-stayed main bridge. This section of structure comprised a short length of at-grade guideway, about 214 metres of twin three-span elevated guideways, the north abutment, and two intermediate piers.
BC Transit invited Associated Engineering to prepare a design using structural steel, in competition with a concrete design prepared by others. The guideways for this section turn through some 60 degrees in plan, with minimal 200 metre radii and spiral curves, maximum 9.3% superelevation and maximum 6% longitudinal grade. Coupled with the lengthy 74 metre spans and stringent seismic design requirements, design engineers faced a considerable challenge. An unstable retaining wall and slope supporting Columbia Street adjacent to a 25 metre high support pier presented further difficulties. The lack of working space for temporary support during construction posed another design consideration. In addition, the design of the bridge had to minimize its visual impact from Columbia Street.
When both the steel and concrete designs were tendered, Associated Engineering’s steel design proved to be 20% less costly than the concrete alternate. Despite the considerable size and curvature of steel girders, erection of individual units up to 76 metres in length, using a single crane, proved to be straight forward. Moreover, the guideway design produced the visual effect of lightness and grace.