The Alexandra Bridge, also called the Interprovincial Bridge, is designated as a National Historic Civil Engineering Site on the basis of “the outstanding ingenuity and foresight of Canadian Engineers” who designed and constructed the structure between 1898 and 1900. A tourist attraction due to its historic status and its impressive view of Parliament Hill, the bridge is also a crucial link between Ottawa, ON and Hull, QC.

Although previous rehabilitation projects and ongoing maintenance have kept the Alexandra Bridge in service for over a century, assessments carried out on behalf of Public Services and Procurement Canada (PSPC) indicate that significant rehabilitation and updates are required at this time. PSPC aims not only to extend the service life of the bridge through this rehabilitation, but also to preserve the heritage character of the structure.

On behalf of PSPC, WSP Canada Group (WSP) engaged SHM Canada to design, install, and operate a Structural Health Monitoring (SHM) system to monitor strain in selected truss members of the Alexandra Bridge. Assessment of heritage structures, like the Alexandra Bridge, presents many challenges. Factors such as rusting, corrosion, and a long history of different repairs and rehabilitations may make traditional forms of assessment, such as surveying the movement of expansion joints, less accurate than they might be in a newer structure.

Our SHM system addresses these challenges by continuously recording exact temperature and strains at key points of the structure. The system comprises an array of strain gauges and Digital Sensor Interface (DSI) units with incorporated temperatures sensors. These units were placed strategically on critical members of the bridge structure and connected via cellular network to our servers. The precise data gathered by our system determines the global thermal behaviour of the bridge with greater accuracy than is possible from conventional assessments and contributes to the development of an efficient, cost-effective strategy for rehabilitation of the bridge structure.

The system utilizes DSI units that were developed in-house by SHM Canada, resulting in improved signal quality while achieving a significant reduction in the length of signal cables, as compared to conventionally wired systems.