Development And Calibration Of Embedded PZT-Based Danamic Stress Sensors

Recently,the Lead Zirconate Titanate(PZT) are widely used in the health monitoring and damage identification of civil engineering structures owing to its characteristics: fast response;wide frequency range; good linearity; appropriate piezoelectric constant; cheap price. It can be used as sensors and actuators simultaneously. In order to realize the real-time monitoring of break in the concrete structures, embedding the PZT into the mortar block which is compatible with the concrete and is embedded into the concrete structure as a sensor or an actuator.Reinforced concrete building structures with poorly detailed transverse reinforcement are vulnerable to shear failure, so the real-time monitoring of stress is the primary way to ensure the security of the concrete structures. In the laboratory,the resistance strain gage attached to the surface of concrete structure are used to measure the strain and then by the use of Young's module to get the result of surface stress via the corresponding conversion, but we could not obtain the internal stress state of the concrete structures. Moreover, Young's module is not a constant when material is in plastic stage. So the measurement of internal force is very important for concrete structures under the operating state. The exploitation of sensors have great significance in the measurement of concrete inner force,especially in the measurement of dynamic loads.The article propose a PZT-based sensor and then ccalibrate its sensitivity.(1) For the dynamic stress measurement, a PZT-based dynamic stress monitoring sensor was developed. The design and the structure of the developed sensor and the methods for the improvement of stability of the sensors are described.(2) The developed dynamic shear stress sensors using shear type PZT patch are embedded in a hollow thin-wall concrete cylinder with enough diameter-thickness ratio. Using a small dropping hammer machine to apply dynamic force to the cylinder, the sensitivity of shear PZT-based stress sensors under the dynamic loads was determined. The experiment results show the output of the developed shear sensor has an good linear relationship with the shear stress applied on the sensor and the shear force sensor performs good dynamic response. The variation between the sensitivilities of same type of sensors is limited.(3) For the measurement of stress in concrete structure, a planar stress sensor was developed by using shear type and length-expanding type PZT patch. By the use of a free falling weight, an impact load was applied on the simply supported beam to calibrate the sensitivity of the planar stress sensors. The results showed that the developed internal stress sensor can be used to measure the stress distribution in the reinforced concrete beam.