Experimental Study On Interface Debonding And Concrete Defect Monitoring Of Concrete-filled Steel Tube Column Based On PZT

Concrete-filled steel tubes (CFSTs) have been widely employed in civilinfrastructures such as large-scale industrial plants columns, equipment framecolumns, subway station columns, high-rise and super high-rise buildings and bridgestructure because of their excellent structural performance including higherload-carrying capability, good ductility, and convenience and economy in construction.Defect in the concrete core and interface debonding between the concrete core andsteel tube will lead to the reduction of the load-carrying capability and the ductility ofthe CFST members. But due to the invisibility of the interface debonding between theconcrete core and steel tube and the possible damage in the concrete core, it isdifficult to directly detect by general inspection methods. Especially in recent years,many large cross-section complex CFST specimens have been employed in superhigh-rise buildings.In decades, the development of smart materials provides new approach for thelong-term real-time structural health monitoring(SHM) of civil engineering. Smartpiezoelectric materials such as the piezoelectric ceramic(PZT) can be employed asboth actuators and sensors and has superior characteristic including low price, quickresponse, broadband frequency and good linear relationship. Theoretical andexperimental study on the application of PZT for reinforced concrete structures havebeen carried out. In this study, PZT is employed to detect the interface debondingdamage and concrete core defect of CFST specimens. The main consents of this studyare described as follows:Firstly, a new generation embedded PZT based function element is introduceddetail. Meanwhile, experimental study is carried out for validating the performance ofthe active SHM system using embedded PZT based function element for CFSTcolumn. The results show that the basic performance of the system such as linearity,sensitivity, stability and frequency characteristic are very good.Secondly, the propagating attenuation behavior of the stress wave produced byembedded PZT based function element in the CFST column is experimentally studied.The results show that the relationship between the amplitude of the received signalsand the excitation frequency approximately takes the exponential form, andattenuation coefficient is the function of the cubic polynomial of frequency approximately. The experimental result can be used for the determination of locationand arrangement of function element in the CFSTs.Thirdly, a CFST column in the laboratory with the artificially mimicked interfacedebonding damage and the concrete core defect is experimentally studied using thestress wave propagating method. Select the different characteristic parameters of thesignal in time domain and frequency domain as object of study and propose a varietyof damage index based on the wavelet-packet energy, amplitude and power spectraldensity to identify damage of the CFST column effectively. The results show thatthe proposed damage identification method for CFST members based on the stresswave propagating method is feasible and effective.Fourthly, on the basis of damage identification method based on wavelet-packetenergy parameters，use the stress wave propagating method to monitor the full-scalelarge cross-section on-site CFST columns without damage of a super high-risebuilding. The results and laboratory results and drill core sampling results coincidewith each other, and verify the applicability of the proposed damage monitoringmethod of CFST in actual project.Finally, condition evaluation of CFST columns of a high-rise building underconstruction using the proposed method is carried out. The interface conditionbetween steel tube and concrete and the quality of the concrete core is evaluated bythe damage index based on wavelet-packet energy.