July 1997

USE OF FREQUENCY DEVICES, INC. EQUIPMENT ON THE CONFEDERATION BRIDGE

Mike Montreuil, TTC/NRC

The Confederation Bridge is one of the world’s longest continuous prestressed-concrete box-girder bridges built over sea water. The main part of the bridge is over 13 km long, crossing the Northumberland Strait from Borden, Prince Edward Island and Cape Tormentine in New Brunswick.

A multi-year monitoring and research project has been established to study the performance of the bridge. To this end, a state-of-the-art distribution data logger system measures ice load, thermally induced stresses and bridge dynamics such as tilt and bridge vibration on a instrumented bridge pier.

To measure the ice forces on the instrumented bridge pier, twenty-eight ice load panels were installed on the pier’s ice shield. Each ice panel is divided into eight impact zones which function as load cells. Each zone produces a signal from a Wheatstone bridge comprised of strain gauges. In order to convert the 224 differential signals to single ended signals, four FDI 5016 multi-channel signal conditioning racks are used. The single ended signals are band limited to approximately 5 Hz using Frequency Devices DP74 Series low-pass 4-pole Bessel filters which are located on 5016-4FF/DP74 quad cards. The amplified and filtered ice load panel signals are then sent to two high speed data loggers.

In order to measure the bridge dynamics under high wind conditions, seismic activity or from vehicular traffic on the bridge, a suite of 75 accelerometer signals are distributed throughout a 1 km section of the bridge. The accelerometer signals are sent to Frequency Devices 8044-3, eight channel filter mounting assemblies populated with D68L8L-50.0 Hz and D64L4L-5.00 Hz low-pass 8- and 4-pole Bessel filters which serve as anti-aliasing filter boards for the accelerometer signals before they are sent to high-speed data loggers that are distributed along the same 1 km length of bridge. The 8044-3 boards were chosen because they could be mounted in the NEMA4X junction boxes that house the data loggers.

More information on the Confederation Bridge monitoring project can be found by visiting the project web-site at http://www.ocbri.carleton.ca


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