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The Canadian Highway Bridge Design Code (CHBDC) uses the concept of a target reliability index for evaluating the load carrying capacity of existing bridges. This index, which is based on risk to human life, relates to three aspects of uncertainties inherent in a bridge; (a) element behaviour, (b) system behavior, and (c) inspection level, where the inspection level currently refers to only manual inspections. Citing examples of tests on many instrumented bridges, the paper proposes an additional inspection level for inspections done with the help of electronic instruments and tests under controlled vehicle loads. The paper proposes simple additions to clauses of the CHBDC, for use when determining the optimum load carrying capacities of existing bridges where structural health monitoring (SHM) information is available.

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Summary It is critical to detect cracks in steel girders of bridges before they have the potential to compromise the integrity of the structure. Both distributed binary sensors and distributed fiber optic sensors are capable of detecting cracks that are wider than 0.2 mm in steel girders. The objective of this paper is to report the optimum placement of these sensors on the girder to detect smallest possible length of the crack. In this work, the optimized placement of crack sensors was studied using FEM of two typical medium‐span simply supported steel girder bridges (Girder A, 30‐m–long span, and Girder B, 22‐m–long span). Using loads estimated from field monitoring data and FEM, a map of crack opening along the length of the crack was calculated for stable crack lengths. Using these maps and given the detectable crack opening of 0.2 mm, the optimum place to position a distributed crack sensor to detect the smallest crack length was determined. For Girder A, the sensor should be placed at 150 to 250 mm above flange at midspan and at one third from the support, and for the rest of the length of the girder, it should be placed at 200–300 mm above the bottom flange. For Girder B, the optimum placement for installation of binary sensor is estimated to be at 150 to 220 mm above the tension flange. The proposed method of calculation of placement can be used for installation of distributed sensors on other types of bridges.