Seismic Stress Monitoring For RC Structures Based On Piezoelectric Smart Aggregates

Earthquake is a main reason which causes structure damage. As an important structure form, the reinforced concrete structures will be significantly damaged by earthquake. At present, there are few methods which could monitor dynamic damage process of concrete structure reliably and directly. It impacts us on understanding the seismic damage mechanism of structure deeply. Because of the problems above, in this paper, a method for monitoring seismic stress process based on piezoelectric smart aggregate is proposed, focusing on the following research:(1) According to the seismic response characteristics of concrete structure, goals for the maximum stress monitoring of50MPa and lower limited frequency0.04Hz (time period25s) are set. The charge voltage converter circuit is designed based on the piezoelectric constant of PZT, and developed the charge-voltage converter. A charge-voltage converter electrical model is built and formulas on the frequency of the input signal between the charge-voltage converter output voltage amplitude and phase difference are developed. A frequency response test of charge-voltage converter is designed and the test curve is in good agreement with the theoretical one.(2) The piezoelectric smart aggregate for monitoring the RC structure seismic stress response is designed based on the piezoelectric effect. The piezoelectric smart aggregate with compression type PZT as a sensitive element, is wrapped in a pair of cuboid marbles with epoxy. Finite element analysis software ABAQUS is taken to simulate the system. Research on the stress transfer relationship of piezoelectric smart aggregate is done, the stress sensitivity coefficient is obtained and the impact of epoxy layer thickness on the sensitivity coefficient of piezoelectric smart aggregate is studied. A dynamic loading test by the servo-hydraulic testing machine (MTS810) is taken. The stable process of piezoelectric constant under static load and impacts of initial stress levels on the degradation performance of PZT piezoelectric constant is discussed. Investigation shows that the compressive sensitivity of smart aggregates is not sensitive to the pre-stress. The result of sensitivity coefficient shows that the experimental and finite values are in good agreement.(3) Similar to the normal stress monitoring piezoelectric smart aggregate. Shear stress monitoring piezoelectric smart aggregate with shear type PZT materials as sensitive elements is designed. ABAQUS is taken to study the stress distribution of the piezoelectric smart aggregate and the theory value of sensitivity coefficient of shear stress is obtained. A shear stress loading mold is designed, which can apply a pair of anti-symmetric to the two surface of piezoelectric smart aggregate, The servo-hydraulic testing machine (ServoPulser4890, Shimadzu) is taken to carry on the dynamic shear stress loading test, and the test value of sensitivity coefficient are is got. Finite element analysis under the shear stress model is taken to analysis, the stress distribution and theory value of the stress sensitivity coefficient is studied. The theoretical results agree well with the test result, which indicates that the finite element model is reliable. A monotonic loading test is carried on the piezoelectric smart aggregate until failure with this mold to study the monitoring performance of the piezoelectric smart aggregate in the cracking process and the result shows that piezoelectric smart aggregate will underestimate the stress value in the cracking process.