Study On Ultrasonic Test Of Concrete Beams Under Eccentric Compressive Stress Field

Ultrasonic coda wave testing technology has been making important progress in the past decade,and it has approached the breakthrough of concrete structural stress testing.In the process of using ultrasonic coda wave testing technology to test the stress of concrete structure,the research object has been extended from the one-way force test block to the complex force component which is closer to the actual situation.The purpose of the research is to explore the functional relationship between the parameters of the ultrasonic coda waveform signal and the stress fields in which the concrete structure is located.This paper studies the content of the“ Analysis of Ultrasonic Coda Wave Time-domain Signal Parameters under Eccentric Compression Stress Field” in the National Natural Science Foundation of China(Grant No.51478072),and takes a reinforced concrete I-beam as the research object,combines the ultrasonic coda wave test of the concrete beam under the simple stress field has been carried out in the previous stage of the research group.The ultrasonic coda wave test under the eccentric loading condition of the reinforced concrete I-beam is designed and implemented.On the basis of verifying the stability of the test data under the self-weight state and the maximum eccentric load,the cyclic eccentric loading test of the I-beam is carried out,and the numerical analysis algorithm program based on singular value decomposition is compiled.An approximate linear relationship between the amplitude eigenvectors of the ultrasonic coda waveform and the load levels is established.The main research content is as follows:(1)Focus on the research work on the stress test of concrete structures carried out by using ultrasonic coda wave,and clarify the research content and technical route of this paper.Summarize,organize and analyze the principles,experimental schemes,data processing methods and research results of relevant research at home and abroad.Based on this,the basic experimental research under the three-point bending load is carried out,based on the analysis results of the test data,the research technique of using the amplitude eigenvector of the ultrasonic coda waveform to characterize the loaded system of the beam is clearly proposed.(2)A time-domain measurement model of ultrasonic coda waveform amplitude eigenvector based on singular value decomposition is established.Based on the theoretical derivation of the singular value decomposition process,the corresponding numerical analysis algorithm program is compiled by MATLAB.Taking the load level under the eccentric compressive stress field as the function independent variable,the waveform amplitude eigenvector after the singular value decomposition as the function dependent variable.A measurement model using the amplitude eigenvector of the ultrasonic coda waveform to characterize the load level is established.(3)The time-domain test study of ultrasonic coda wave of reinforced concrete I-beam under cyclic eccentric loading is designed and implemented.The parameters setting of ultrasonic coda wave testing instrument,the design and manufacture of the test beam,the arrangement and position of test measuring points,and the eccentric loading method are preliminarily worked out.The ultrasonic coda wave test was carried out on the reinforced concrete I-beam under the self-weight state and the maximum eccentric load,and the stability of test data is evaluated.On this basis,cyclic eccentric loading is carried out on reinforced concrete I-beam,the ultrasonic coda wave test data under different load levels are collected.Using the above-mentioned programmed MATLAB algorithm program to carry out systematic analysis on the experimental data,and an approximate linear relationship between the amplitude eigenvector of the ultrasonic coda waveform and the load levels is established.