Bridges

The development of a long-term electrolyte gel will enable MFS to test for cracks in bridges over the long-term, lasting months instead of days. MFS would offer this enhanced EFS System as part of an overall long-term bridge monitoring system, many of which are being implemented across the country. Typically, these ongoing monitoring systems include video cameras, weight and temperature sensors, and other technologies to ensure vehicle safety and provide the bridge owner with extensive knowledge of bridge status.

Electrochemical Fatigue Sensor

The technology behind EFS was originally devised by researchers for the U.S. Air Force and the University of Pennsylvania for use in the aerospace industry. The original research was aimed at developing a technology for detecting problem cracks in airframes and engines.

Since that time, additional research and development has resulted in the adaptation of the EFS system for steel bridge inspection. In 1993, they forged a development deal with MFS, which revamped the technology for bridge inspections between 2002 and 2006.

To use the EFS on bridges, inspectors first identify the vulnerable parts of a bridge. These could be the areas most susceptible to wear and tear — say, a sharp corner or a welded connection — or places where bridge owners already suspect a crack.

Then they wire up the areas with sensors, which are similar to the peel-and-stick versions used for an EKG reading. Finally, they apply a constant electrical current that runs between the sensors and the bridge.

By assessing the behavior of the current as it passes through the metal, the sensors can detect cracks down to a hundredth of an inch in size. And because the device is operated while the bridge is in use, it can determine how the cracks change as the structure flexes under stress. MFS’s software analyzes the resulting data to determine whether cracks are staying the same size or growing.

Fatigue Fuse (FF)

The Fatigue Fuse (FF) is a thin piece of metal consisting of a series of parallel metal strips connected to a common base, much as fingers are attached to a hand. Each of the fingers has a different geometric pattern. By applying the laws of physics in predetermining the geometric contour of each finger, the fatigue life of each of the fingers are finite and predictable. When the fatigue life for a given finger (or fuse) is reached, the fuse breaks.

By using different geometry for each finger, different increments of fatigue life are measurable. Typically, these fingers are constructed to fail at increments of 20% of the metal’s fatigue life. By mechanically attaching or bonding these devices, the Fuse undergoes the same strain sequence as the structure. As the fuses break, they indicate the increment of fatigue life reached for that area of the structure.

The FF is especially useful in monitoring the condition of movable bridges and has been used by the Army Corps of Engineers for this purpose. Fatigue Fuses have been applied to movable aluminium bridges for the US Army, made by a division of General Dynamics, Inc. No special training is needed to qualify individuals to report any broken segments of the FF to the appropriate engineering authority for any necessary action.

brent_driggersBridges