Experimental Study Of Ultrasonic Testing Stability Of Reinforced Concrete I-beams

Ultrasonic testing of stresses based on elastic waves is one of the important research directions in nondestructive stress testing.Since Hughes and Kelly proposed the acoustoelasticity in 1953,researchers have been improving and developing theories and techniques concerning the testing of structural stresses based on elastic waves.An important part of the research is the detection of disturbances in the elastic waves,which still have fluctuations even in ultrasonic testing of concrete stresses in a laboratory environment.Therefore,this paper investigates the stability of ultrasonic testing of stresses in concrete I-beams,focusing on the effects of test results caused by fluctuations in the laboratory environment and the instrument.(1)The ultrasonic testing techniques for concrete stresses,especially for stability issues,are investigated in the literature.A variety of existing technical routes using direct wave,coda wave,acoustic time,wave velocity and waveform distortion were reviewed;the literature on ultrasonic tests subjected to interference such as temperature and humidity,as well as bias control techniques,optimal baseline subtraction and other processing methods were highlighted.According to the research results,the technical route and the algorithm of orthogonal projection for stress testing using waveform distortion for concrete I-beams are clarified in this paper,and the energy method is adopted to quantify the effects of fluctuation on the results.(2)Optimized the contents of the stress ultrasonic testing of concrete beams regarding the stability test procedure,adjusted the original test scheme of repeated loading within one day,lengthened the continuous test time of each level of loading(each level of loading lasts for 1 day),investigated the volatility of each level of loading within 1 day,implemented this test scheme,and obtained the corresponding ultrasonic test data matrix(20 levels × 2800 waves × 1024 points/wave);the temperature and humidity of the test environment,the temperature of the beam and the apparatus were also recorded.Preprocessing and preliminary analysis of the above two types of data were carried out,and the results showed that the changes of the same level of load in the waveform and the changes of temperature and humidity have a certain correlation.(3)Deepening the singular value decomposition algorithm,constructing a normalized characteristic vector based on the singular value decomposition,improving the calibration curve of the stress field under a specific load;adding the projection indicator-stress(load)indicator mapping relationship based on the stress(load)indicatorultrasonic waveform,and refining the measurement model of ultrasonic testing of the stress to be measured in I-beam concrete.(4)Quantify the influence of noise(interference)on test results and analyze the proportion of noise(interference)distribution in the high-dimensional space.The projection-orthogonal relationship in the high-dimensional space is used to decompose the ultrasonic data into load projection waveforms in the direction of the characteristic vector and orthogonal waveforms in the direction of the characteristic vector orthogonality.The noise statistical characteristics of the recorded,projected and orthogonal waveforms were analyzed in terms of error waveform and noise energy,respectively,and the results showed that the noise content of the projected waveform was significantly lower than that of the orthogonal waveform.