| Void and debonding defect of steel-concrete composite structure will significantly weaken the combined effect of steel and concrete,which seriously endangers the safety and durability of practical engineering.However,most of the existing non-destructive testing technologies have problems such as easy misjudgment,incomplete acquisition of defect features,and unintuitive results.Therefor,synthetic aperture focusing imaging technique(SAFT)and piezoelectric ceramic testing technique are used to realize the non-destructive,quantitative and intuitive detection of debonding defects at the bonding interface of steel-concrete composite structures(concrete-filled steel tube and steel-concrete slab).And carry out the related algorithm improvement and experimental verification.This article involves mainly the following work and corresponding results:(1)For the first time,SAFT is introduced into the detection of void defects at the bonding interface of concrete filled steel tube.Aiming at the multi-layer structure of concrete-filled steel tube(CFST),the root-mean-square(RMS)wave velocity of multi-layer materials is used to replace the wave velocity of a single material for the calculation of horizontal sound time.The conventional SAFT algorithm was also improved by using wavelet noise reduction and Fourier frequency domain filtering to reduce noise on the original signal.(2)Several groups of CFST specimens with different types of defects were produced to test and compare the effectiveness and accuracy of the algorithm before and after the improvement.The results show that,both the traditional SAFT algorithm and the improved SAFT algorithm can effectively image the type I and type II spherical cap debonding defects,that is,the SAFT is generally feasible and intuitive to detect debonding defects in CFST.The average error of the imaging position of the improved SAFT algorithm for the two types of spherical cap debonding defects is only 0.4%,which is significantly lower than that of the traditional SAFT algorithm(4.0%).And the noise is significantly reduced in the imaging results.The imaging quality and imaging position accuracy of the improved SAFT algorithm for the two types of spherical cap debonding defects are significantly higher than traditional SAFT,thus having a higher engineering utility value.(3)The debonding defect identification test of CFST based on piezoelectric ceramic surface wave signal testing technology was conducted.And the detection effect of this technology is compared with that of SAFT technology.The results indicated that,the type I spherical cap debonding,type II spherical cap debonding and peripheral uniform debonding defects can be effectively identified by analyzing the parameters such as peak,wavelet packet energy and loss index of the received signal.In addition,it is found that the piezoelectric ceramic test technology can roughly judge the length of the debonding defect,and the SAFT can identify the thickness of the defect.Therefore,it is suggested to combine the two methods in CFST to obtain the full characteristics of the debonding defects.(4)The debonding defect identification test of steel-concrete slab based on piezoelectric ceramic volume wave was conducted.In order to provide effective detection means for the composite structure which is not suitable for surface wave detection(Such as external wrapping thick concrete layer structure),the influence factors of the received signal are analyzed.The results show that,the thickness of the structure and the reinforcement mesh in the concrete have less influence on the signal,and the excitation voltage,excitation frequency,debonding thickness and the layout of sensors have a greater influence.For steel-concrete composite slabs with a single layer of steel plate,it is advisable to place the excitation sensor on the opposite side of the defect for detection;while for multi-layer steel-concrete composite slabs with gaps between steel plates,the excitation sensor must be placed on the same side of the defect. |
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