Study On Defect Detection For A Large-scale Irregular Multi-cell Concrete-filled Steel Tubular With Electro-mechanical Impedance Of PZT

Along with the rapid development of economic and the accelerated process ofurbanization, the construction scale of high-rise building has been increased.Concrete-filled steel tubes (CFSTs) offer excellent structural performance, such ashigh load-carrying capacity, high ductility and large energy absorption capacity underearthquakes and have been widely used as primary axial load carrying members inhigh rise buildings. Currently, multi-cell concrete-filled steel tubular (MC-CFSTs)with large cross section and irregular shape have been widely employed in the superhigh-rise building structure. If there are defects in the inner part of CFSTs, thecapacity of load will be reduced; also it will cause an accident. Therefore, there arecommon concerns about the uniformity and quality of the concrete as the possibleinterface debonding defects between the steel and the concrete, also the cavity in theconcrete.Lead zirconate titanate (PZT) is one of the most effective types of piezoelectricmaterials, with the advantages of high sensitivity, compact size, good durability andwide frequency response band. Also, it can be used as an actuator and as a sensor fordamage detection simultaneously in structural health monitoring (SHM). AnElectro-Mechanical Impedance (EMI) Method based on PZT was adopted in adetection of defects for MC-CFSTs in this thesis. Aiming at the common defects ofthe interface debonding and the cavity of concrete, experimental studies were taken.In the meantime, a numerical simulation of Finite Element Method (FEM) was appliedto EMI method using ABAQUS. The main contents of this study are shown asfollows:Firstly, the basic principle of the EMI method for SHM was introduced.Meanwhile, the workmanship of the embedded PZT-based functional elements (EPFEs)was presented in detail.Secondly, an experimental study of mimicked interface debonding defects wascarried out on a testing column of MC-CFST. The artificially mimicked interfacedefects of the testing column were made by pasting thin soft wooden plates on theinner surface of the steel tube and the lower surface of diaphragms before pouringconcrete. The surface-bonded PZT patches or the EPFEs were set on the presetpositions according to the plan. The EMI results both PZT patches and EPFEs are measured by an impedance analyzer and are employed to detect the interfacedebonding defect. The preliminary analysis results obtain from the impedance figures.Taking the root mean square deviation (RMSD) of the measured EMI as a damageindex; results show that the damage index is sensitive to the interface debondingdefects. What’s more, the proposed approach is capable of detecting the interfacedebonding defects.Thirdly, an experimental study on the defects of the cavity in the concrete for thetesting column of MC-CFST was conducted by using the hard wooden box forartificially mimicked cavity defects. In terms of the plan, the PZT patches or theEPFEs were arranged at the preset positions. The impedance figures show thepreliminary analysis results. The RMSD and the impedance figures all demonstratethe effectiveness of detection of inner cavity defects for using EMI method.Finally, a numerical simulation was applied to EMI method based debondingdefect detection of MC-CFST by using the harmonic response analysis method instructural dynamic steady-state from ABAQUS. Through the analysis and comparisonof the results, it indicates that the EMI method is feasible and effective for the defectsof CFST.