Study On Damage Detection Of Concrete Structure Using Guided Wave And PZT Smart Rebar

Structural health monitoring(SHM)techniques based on piezoelectric ceramics have been developed greatly recently.Many researchers tried to apply these techniques for damage detection in civil engineering.Reinforced concrete is one of the mostly used materials in high-rise buildings and infrastructures,where the safety and stability is the key related to the peoples who live and work there.Therefore the study of active damage detection is with great significance.In previous researches,rebar debonding damage in concrete structure was successfully detected using smart rebar active sensing system,the relationship of output signals and debonding sizes was obtained and damage index was developed.Based on the previous study,the mechanism of detecting other types of damage has been studied,which provides a foundation for real-engineering application.The major research work includes:(1)The working principle of PZT transducer and guided wave method were introduced.By summarizing the previous work on PZT rebar active sensing system,the difficulties and challenges of using PZT rebar for concrete structures' SHM have been raised up.(2)The strength of signals of sensor output was too low for real application because of the high damping of wave energy in concrete.In this study,optimization method of smart rebar system using increasing numbers of PZT elements,changing the installation method of PZTs and changing PZT sizes are proposed.Optimization by changing PZT layout and size are studied in this paper through experimental tests and 2D numerical simulation.Both results have been shown that the output signals have been increased significantly with magnitudes by changing PZT layout and enlarging PZT size.(3)The relationship between output signals of smart rebar and the thicknesses of concrete layer around the rebar has been researched by tests and simulation.Previous 3D model is optimized in order to reduce the calculation time.Both of two test results showed that output's amplitude of smart rebar is decreased exponentially with the thickness of the covered concrete on the rebar.Model with CA layer fell-off has been set up,results show CA mortar layer's fell-off led to the amplitude of output signals be increased observably.This leads to the potential monitoring of CA mortar layer using smart rebar active sensing system.(4)An active sensing diagnostic system based on PZT network for crack detection is proposed,and the influence of cracks on the propagation of stress wave is analyzed.Concrete beams with full-size have been cast for experimental tests,and artificial cracks with different depth and different numbers were made to mimic the development of cracks.Test results show that the amplitude of sensor output signals is deceased linearly with a crack depth,and is decreased exponentially with the increased crack numbers.The results prove that the network system made by PZT rebar could be used to detect cracks in concrete structures.