Creative Construction Method for an Attractive Tied Arch

The City of Chilliwack is replacing an important bridge over the Vedder River using the design build project delivery model. The winning design was an attractive 60m twin tied steel arch bridge with steel hanger rods in a “ray” arrangement. The longitudinal tie girders for the arch is a steel box section which connect the ends of the pipe arch ribs, and support transverse floor beams. The tie girders are made continuous through a 20m south side span. In-river works were undesirable due to fisheries windows schedule limitations. Launching was therefore chosen for the erection method. This presented unique challenges for an arch due to high abutment reactions on the underside of the tie girders during the launch. A temporary kingpost design was developed to support the midspan of the arch during the launch. The continuous south side span tie girders will act as a launching nose. The kingpost will also be used to support the old truss bridge during demolition.