The Thousand Islands Bridge  is long-span bridge crossing the border between Ontario and the state of New York. Built in 1937, this bridge sees over 2 million commuters each year travelling through the Lansdowne border station.

The entire bridge spans 13.7km and is a hybrid-suspension bridge featuring very active expansion joints. Due to a large amount of traffic and its structural tendency to move, Transport Canada alongside the Federal Bridge Corporation LTD. approached Sensequake to test the bridge.

The 500m section we evaluated proved to be challenging, due to its long structural shape. Our 3-day sensing test was therefore designed specifically with its span in mind, with long data collection times which were used to achieve relevant results. This test included:
 

• Defining a baseline for the bridge

• A global test of the bridge

• Sectional tests between the side and central spans

• Joint tests at the compression joints throughout the bridge
   

All modal properties were examined through the post-processing of the data. These include the natural frequencies, the damping ratios and the mode shapes of the entire bridge.

Additionally, the reactions between the compression joints were examined separately to identify the interaction between the sections. While the finger joints exist between the main and side spans of the bridge, they are attached by the steel cables. Sensequake, therefore, had to create a specialized test to take this into account and properly examine the behaviour between the side and midspans of this bridge.

Within the mandate, Sensequake was equally responsible for the testing of a nearby short, rigid bridge operated by the same client. Thanks to our approach relying on ambient vibration analysis, our team was able to determine the dynamic characteristics of the structure even with its high rigidity and multiple modes.