DYNA Force® Elasto-Magnetic Sensor
There is a large demand for implementing health monitoring of bridges, buildings and underground structures. Post-tensioning is a key element to the performance and durability of these structures. On many occasions during the construction and service life of the structure, it is useful to know the force in the post-tensioning system. Although there are many methods to measure the tendon force, most of them are cumbersome, expensive, and the accuracy varies depending on the method used. DSI is actively involved in the development, testing and utilization of the DYNA Force® System for measuring the force in post-tensioning tendons.*
DYNA Force® Sensors are based on the magneto-elastic properties of ferrous material. The permeability of steel in a magnetic field changes with the stress level in the steel. By measuring the change in permeability, the stress in the steel element can be determined.
The sensor does not alter the characteristics of the tendon other than its magnetization where the sensor is installed. A readout unit is designed to magnetically energize the steel through the sensor and measure the response of the steel to the process. The readout unit then converts the response into a direct force reading. The sensor has an embedded thermistor which allows for temperature compensation. Due to the diversity of the magnetic property of steel, calibration is done for each type of steel, allowing the sensors to perform at their highest accuracy.
The DYNA Force® System allows the user to regularly monitor the forces in the post-tensioning system in minutes as a part of the inspection procedures without the need for lift-off equipment or other special expensive techniques.
The system avoids the inaccuracies and risks associated with lift-off readings.
The DYNA Force® Sensor is robust, requires no maintenance, has no moving parts and is not subject to any load. It is expected to have a similar service life to that of the surrounding structure.
DYNA Force® Sensors are cylindrical in shape and are installed over strand / bar prior to stressing. They can be used for bare, epoxy-coated, galvanized and greased-sheathed steel in the bonded, un-bonded, grouted or ungrouted length of the tendon. The DYNA Force® System is known for accuracy, its performance, ease of installation, durability, and cost effectiveness.
* The DYNA Force® System was developed in partnership with the supplies of the PowerEM® System: Intelligent Instrument System, Inc.