Dawson Bridge over the North Saskatchewan River has served the people of Edmonton for nearly 100 years. A five-span riveted steel through-truss, it was originally constructed to carry electric trains to a coal mine located on the east bank. Later converted to carry highway vehicles, the bridge currently accommodates 17,000 vehicles per day along with significant pedestrian and cyclist traffic. In 2007, a bridge condition assessment revealed that the superstructure was in need of significant repair, including bridge deck replacement and truss repainting. Field inspection and structural analysis also identified numerous truss members requiring strengthening or replacement to provide an appropriate level of safety and extend the service life of the bridge. Presented as a case study, the paper includes the rationale for selecting the rehabilitation strategy for the bridge. The paper will focus on an innovative strategy for replacing the existing concrete deck with a proprietary composite steel plate and elastomer lightweight deck system. This system, known as SPSTM makes use of two relatively thin steel face plates connected by an injected thermosetting elastomer core. The final product is a composite panel with high stiffness and strength, but relatively low weight. Dawson Bridge is the largest project in the world to incorporate this innovative deck system. The paper also discusses the importance of a structured risk control plan in the implementation of new technologies. Perceived risk—and its associated liability—often dissuades engineers from trying innovations that might advance the state of the art for the long-term benefit of society. Striking the right balance between innovation and risk control is the key to success.
