Study On Internal Defects Detection Method For Concrete Filled Steel Tube With Surface-mounted Piezoceramics Patches

Concrete filled steel tube(CFST)structure has been widely employed in high-rise buildings as a kind of typical composite structure taking advantages of concrete and steel to carry axial or vertical loadings.Due to insufficient vibration,complicated inner strcture and shrinkage and creep of mass concrete after concrete pouring,defects in concrete core and interfacial debonding between concrete core and steel tube occur possibly,which weaken the mechanical properties of CFST.Therefore,it is critical to develop efficient internal defects detection approaches for CFST structures.In this study,an internal defects detection approach for CFST members by the use of surface-mounted piezoelectric lead zirconate titanate(PZT)patches is proposed and experimental and numerical studies on the feasibility of the developed approach are carried out.The main contents of this study are as follows:(1)After making brief introduction on the development of PZT based damage detection methods for civil engineering structures,the principle of the detection approach for internal defects including the interface debonding debonding and the concrete core void by the used of surface-mounted PZT patches are introduced.Moreover,the fabrication and installation method for the external surface-mounted PZT patches and the test setup are introduced.(2)Aiming at the interface debonding defect detection for CFST columns with surface-mounted PZT patches,a rectangular CFST members with different interface debonding defects is designed and constructed.Two measurement approaches where the PZT sensor is located on the same side or the opposite side of the PZT actuator,respectively,are studied.Using the PZT sensor measurement either on the same side or on the opposite side of the PZT actuator,the effect of the interface debonding defect on the measurement can be observed.At the same time,when using the measurement of the external surface mounted PZT patches on the same side of the PZT actuator with equal spacing,the interfacial debonding location can be detected.Moreover,tests on a set of planar CFST specimens with interface debonding defects also show the interface debonding defect can be detected efficiently with the PZT measurement on the opposite side of the specimens.(3)Aiming at the concrete core void detection,a set of planar CFST specimens with different concrete core void defects were designed and constructed.Measurement of the surface-mounted PZT sensor on the opposite side of the PZT actuator is made to investigate the effect of concrete core void and results show that the measurement of the surface-mounted PZT is affected by the concrete core void and the proposed approach using surface-mounted PZT actuation and sensing is efficient.(4)In order to investigate the defect detection mechanism for CFST members using surface-mounted PZT patches,numerical simulation is carried out to study the effect of both interface debonding defects and concrete core void on the measurement of PZT sensor.Considering the piezoelectric effect of PZT sensor and the inverse piezoelectric effect of PZT actuator and the coupling effect between them and CFST,a two-dimensional multi physical field coupling finite element model is established.The change in output voltage signal amplitude of PZT sensor measurement corresponding to specimens with different defects under sinusoidal excitation and sweep excitation are studied by numerically,respectively.At the same time,the difference of stress wave field of two-dimensional CFST specimens with different defects under point load is also analyzed to demonstrate the effect of defects on the stress wave fields.(5)Finally,based on the findings from this study,the proposed approach is employed to detect possible defects in CFST members of a super high-rise building under construction.The defect evaluation index is obtained through the field measurements and results show that the defect evaluation index of the tested CFST members is in a reasonable range and no obvious defects in the CFST can be observed.According to the experimental and numerical simulation results,the existence of internal defects of CFTS members can be detected by the surface-mounted PZT sensors and the proposed approach provides an easy way for the defects detection of CFST members.