Experimental Study On Structural Damage Monitoring Based On PZT-Impedance For RC Structures And CFSTs

The reliability and safety of civil engineering structures is significantlyimportant for human being life and the corresponding property. Effective damageidentification on the structures can provide the basic for evaluating the safety ofstructures. In recent years, the research on structural health monitoring (SHM) hasbeen one of the hottest study fields. The technic by using intelligent materials instructural health monitoring and damage identification is hopeful. As a new type ofstructural health monitoring technic, the application of the piezoelectric ceramicbased electromechanical impedance (EMI) approach (PZT-EMI) on structural healthmonitoring is noteworthy. To date, the study on the damage identification usingPZT-EMI approach on RC shear walls and columns after dynamic cyclic loading isless carried out. Moreover, there are few available literatures on the damageidentification approach by using the PZT-EMI for evaluating the debonding betweenthe steel tube and core concrete in concrete-filled steel tube (CFST) columns. Basedon the previously mentioned background, the EMI-PZT approach was used to detectthe cracking damage of RC shear walls and columns after dynamic cyclic loadingand interfacial debonding damage in CFST columns. The main contents of this thesisare shown as follows:(1) Firstly, based on the state-of-art of the application of the PZT-EMI approach,a damage identification test was carried out on a group specimens of steel rebar withdifferent extent degree of damage using the PZT-EMI approach. It can be found fromthe test results that as the extent of the damage increases, the peak values ofimpedance curves decrease and offset. Test results on multi-loaction with differentextent of damage indicate that the damage index has relationship with the damageextent of the steel. This experiment validate that the proposed approach is feasible tomonitor and identify the steel rebar damage.(2) The fabrication of PZT based embedded multi-functional element wasintroducted in detail firstly. Then the EMI approach based on the embeddedmulti-functional elements pre-embedded in the reinforced concrete (RC) membersand surface bonded PZT patches was proposed to detect and evaluate the damage ofRC columns and RC shear walls after dynamic cycle loading. The experimentalresults show that impedance measurements of sensors, which are close to the maindamage area at the connection between the base and the bottom of the column, behaved as descending peak value of impedance and offset of frequencycorresponding to the peak value of impedance. Impedance measurement curves ofsensors nearby the diagonal and horizontal cracks at the top of members behaved asslight fluctuation and offset of peak values. The results from comparison withdamage index of different sensors show that the descending and offset of the peakvalues have relationship with the extent degree of damage.(3) Based on the PZT-EMI approach, damage detection experiment on a CFSTcolumn designed with the damage of interfacial debonding in lab was conducted.From the results, it is found that the impedance measurement curves from the intactsections behaved in coincidence, placidly and smoothly. The impedancemeasurement curves of interfacial debonding area fluctuate at different extent andthe peak values of impedance descend and the corresponding frequecgy offset. Thedescending and offsetting extent corresponds to the damage extent. The experimentdemonstrates that the PZT-EMI approach is effective to detect the interfacial damageof CFST members.(4) Based on the experimental study on interfacial damage detection in CFSTcolumn with EMI-PZT approach, the EMI-PZT approach was used to monitor theinterfacial bond behavior of the large size CFST columns of a super high-risebuilding. The monitoring results indicate that impedance measurement curves fromthe different PZT and embedded functional elements at the same section of thecolumn are almost identical. The damage index was lower than10%at all thesections measured. It can get a conclusion that the interfacial bond behavior betweencore concrete and steel tube should be good and no debonding can be detected.