Alexandra Bridge: A historical infrastructure

This project consists of a structural evaluation, detailed inspection, wind study, condition monitoring program, and rehabilitation of the Alexandra Bridge in Ottawa-Gatineau. The bridge is 575 metres long and consists of steel trusses and solid web girders on steel trestles. Since its construction in 1898, the bridge has undergone several repairs and rehabilitation. Currently, numerous components of the bridge are in an advanced state of corrosion and thermal expansion of the bridge is not occurring at the predetermined locations.

the rehabilitation scope is to ensure the bridge has a remaining life expectancy of 10 years, and covers the following work:

  • Rehabilitation of the boardwalk.
  • Assessment and rehabilitation of the bridge articulation, as required.
  • Assessment and rehabilitation of structural members as required based on the structural evaluation, deterioration, and the wind study.
  • Non-destructive testing and monitoring of bridge members during design and construction and after construction.
  • Due to the short time frame, several teams performed the inspections simultaneously using electronic tablets. Due to load limits on the boardwalk, access was only possible using barges. We provided the client with a complete schematic representation of the bridge including dimensions, comments, and inspection notes as well as the types of deficiencies with dimensions in graphic form, along with spatial references.
  • The use of a complete 3D point cloud of the structure greatly facilitated the verification of the members’ verticality. Scan will also be used again to evaluate the bridge deformations at various temperatures.
  • A wind study was performed to reduce the amount/scope of required strengthening due to wind load. The study included determining the design wind speeds at the bridge site, carrying out a section model study, estimating aerodynamic derivatives and equivalent static wind loads.
  • To further reduce the scope/number of required interventions, a structural monitoring system was installed on the bridge. The monitoring system consisted of 100 strain gauges and 30 acoustic emission sensors. Collection rates are 1 Hz and produce about 700 Mb of data per day. The data was managed by CDJV and used to determine critical areas.
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