Since the monitoring program was launched in 2012 for Champlain Bridge in Quebec, the teams at The Jacques Cartier and Champlain Bridges Incorporated have been using OSMOS solutions to continuously monitor the bridge and perform monthly load testing.
Three indicators to track the impact of daily traffic
More than 300 sensors, optical cables, temperature detectors and expert acquisition stations (EASs) analyze daily traffic indicators every day.
Dynamic events above a certain threshold are automatically recorded, so that data can be provided from 3 seconds before the event to 57 seconds after. The number of events corresponds to the number of dynamic recordings in a given period. Comparing that indicator between different sensors can be used to identify girders that are more flexible and therefore more sensitive to working loads.
In addition to the number of events, the measured deformations can be used to calculate each girder’s deformation and so to identify long-term trends in the girders’ behaviour to target any that show like signs of weakening rigidity. Lastly, the girders’ natural frequency is another indicator, as a girder in good condition has a natural frequency of roughly 2.5 Hz.
Monthly load testing
Each month, load testing is performed by The Jacques Cartier and Champlain Bridges Incorporated. When a 48-tonne truck passes over the auxiliary girders at 10 kph, that is recorded dynamically by the OSMOS monitoring system.
Dynamic mode is activated manually for the duration of the test, to record how the auxiliary girders behave when the truck passes over them.
Because the test transport load is constant, a comparison of the results checks how the condition of the girders changes over time. Once the test is complete, all of the data are confirmed by a team of specialized engineers who analyze the data and present them to the Champlain Bridge Expert Committee.
Confirmation of the effectiveness of reinforcing measures
In light of the rapid deterioration of the auxiliary girders, a girder monitoring and reinforcement program was put in place to ensure the safety of the structure until such time as the replacement bridge is completed. An analysis of the data from the sensors installed on the auxiliary girders is used to measure the effectiveness of the different measures already in place.
These include changing lanes for heavy goods traffic (reducing the number of events recorded for one of the girders by about 66%) and installing modular trusses to transfer weight from the pre-stressed girder to the truss (reducing deformation by 10% and the number of events by up to 95% in certain spots).
About Champlain Bridge
This road bridge, opened in 1962 to connect the cities of Brossard and Montreal over the St. Lawrence River, is the busiest bridge in Canada. With more than 59 million vehicles crossing it every year, it is a strategic economic roadway.
The concrete structure with cantilever girders spans 3,440 metres and six lanes of traffic. Subjected the Canadian climate, Champlain Bridge has aged more quickly than normal.
The rock salt applied during harsh, icy winters has penetrated the deck’s support girders and weakened their internal frame made of steel cables.
After fissures began to appear, namely in the deck, a multitude of measures were implemented to protect the users’ safety: placement of external post-tension cables on the deck girders exposed to the salt, replacement of part of the concrete deck with a steel deck, installation of gutters to channel runoff, reinforcement of the girders, repair work on the access roads and ramps, installation of metal trusses and instrumentation of the bridge with OSMOS optical cables.
In parallel, construction of a replacement bridge was launched in 2015, just a few metres away from the original. It is expected to be completed in 2018.