Research On Health Monitoring Of Concrete Structure Based On Acceleration Sensor Technology

With the social progress and rapid development of economy in recent years, the widespread construction of large civil engineering structures, such as large civilian projects,high-rise buildings, long-span bridges, road infrastructure and water conservancy facilities,etc. greatly promoted the progress of human society. As neglecting the periodic damage detection and real-time, online health monitoring of the structures in their service, Structures are always tend to broken down duo to their damage accumulation and less resistant, which will lead to a sudden major disaster. Therefore, adopting a monitoring method based on intelligent sensor system and data collection and analysis system for civil engineering structure will be increasing significant. Piezoelectric ceramic is a kind of functional ceramics with piezoelectric effect, it is widely used in civil engineering structural health detection/monitoring for not only its sensory and actuating properties but fast response, good linearity, low energy consumption, low cost and easy processing.Piezoelectric acceleration sensor mainly made by piezoelectric ceramic as an important part plays a increasing important role in the field of concrete monitoring/testing. In this paper,for the low coupling with concrete duo to its metal encapsulation, poor water proofing property and durability in existing piezoelectric acceleration sensor, a new type of piezoelectric acceleration sensor with favorable stability suitable for concrete structure is prepared by PZT-5, cement/ polymer, tungsten block etc. it can be embedded in concrete structure and doesn’t change the concrete local characteristics at the same time. Concrete research content includes following several aspects.The preparation and performance research for embedded piezoelectric acceleration sensor. A new type of embedded acceleration sensor was fabricated by using PZT-5piezoelectric ceramic as sensing element, mixture of cement/polymer as encapsulation layer,and tungsten block as mass. Effects of thickness of the piezoelectric ceramics and mass block as a part of sensor on the sensitivity and amplitude-frequency characteristic of the sensor are investigated. The results showed that with the thickness of PZT-5 and tungsten block increases, the sensitivity S of the sensor both increase, the frequency range was gradually decreased, which verifies that the sensitivity and the range of available frequency of the sensor are two contradictory performance parameters, the optimal performance parameters of sensor suitable for concrete low frequency vibration can be reached through coordinating thethickness of the piezoelectric ceramic and tungsten block.The independence of the frequency, linearity and output response in complicated vibration are measured experimentally in testing, meanwhile the identification of modal parameters of a vibration system based on self-made sensors is discussed. The results show the output amplitudes change almost invariably at different frequencies, which illustrates the excellent independence of the frequency of the piezoelectric acceleration sensor. The output responses in both positive and negative installation are consistent and fitted curve possess good linearity, which indicates the high repeatability of piezoelectric acceleration sensor under different conditions. The sensor can accurately reflect the actual vibration of structure in the testing of linear sweep, logarithmic frequency sweep and random frequency vibration.The testing of vibration table system modal parameters shows that sensor can accurately reflects the modal parameters of a simply-supported beam and the damage changes of the structure under attaching mass. Compared the finite element modal analysis with laboratory experimental modal analysis, the results show that the deviation between the structure modal information collected by sensor and theoretical results is small, which is further validated the accuracy of experimental result that the sensor can meet performance requirements in the vibration test.The damage identification of modal parameters of reinforced concrete beam based on the embedded piezoelectric acceleration sensor. The research based on the natural frequency results shows that whether using added mass method, crack-cutting method and three point bending method, with the increasing of the damage degree, which is reflected in the lower stiffness and increasing mass, the natural frequency of reinforced concrete beam about first and second order natural frequency shift to the left, that is to say, the frequency has the tendency to reduce. By comparing the natural frequency changes of reinforced concrete beam under various damage by the finite element simulation, the accurate reliability of the test results is verified, meanwhile reinforced concrete simply supported beam damage location based on the relative variation of vibration mode RD is realized.In order to verify the implantable sensor’s application in the actual engineering situation,Let the reinforced concrete beam- South-to-North water diversion Fan Zhuang road bridge serve as an example, whose single span length is 16.5 m and bridge deck is 7 + 0.75 * 2 m,two methods based on vehicle vibration and natural pulsating are adopted to test the natural frequency, the damping ratio and impact coefficient of the bridge. Compared to the vibration condition of the bridge based on the finite element simulation analysis, the accuracy of thesensor to pick up vibration signals and the practicability of the methods in civil engineering structure health monitoring/testing are verified.