Research On Uncertainty Of Ultrasonic Testing Of Concrete Stress

Stress is an important indicator of structural safety of in-service bridges.The convenience and precision of stress testing is a major research hotspot.In many existing concrete stress test studies,the ultrasonic stress test has obvious advantages,but the test accuracy is difficult to stabilize and guarantee.Ultrasonic stress testing before the application of engineering,it is necessary to conduct measurement research under the framework of uncertainty,find the uncertainty factors that affect the test results,and improve the test accuracy.In this paper,the concrete I-beam is taken as the research object,and the three-point bending load ultrasonic coda wave stress test of concrete Ibeam is designed and implemented.Based on the singular value decomposition,the linear relationship between the amplitude of the coda wave and the stress is extracted.From the angle of view,it was found that vaseline coupling agent,instrument temperature,concrete stress memory,environmental temperature and humidity and other external factors affect the test accuracy.The main work contents are as follows:(1)Conduct research on existing ultrasonic stress testing techniques and measurement uncertainty.Firstly,the existing concrete ultrasonic stress testing technology is investigated.Referring to other technical testing methods and results,a technical route for establishing the correlation between acoustic parameters and stress changes is proposed.Secondly,the research on the measurement uncertainty theory and calculation,from the uncertainty test model and classification assessment,preliminarily clarified the test condition control,uncertainty component determination and its quantization method;(2)Design and implement the ultrasonic test plan for concrete I-beams to complete data acquisition and processing.The reinforced concrete I-beam three-point bending load test device was designed,and the cyclic stress loading and unloading ultrasonic stress test was repeated.Each test was loaded and unloaded with 8 groups,each group was loaded and unloaded with 22 load levels,and 11 waveforms were repeatedly collected for each load shift point.The data processing matlab program is compiled,and the test data is pre-processed.The coda wave waveform characteristics and signal quality are investigated.Based on the advantages of singular value decomposition feature extraction and matrix operation,processing and analyzing the pre-processed test data,established a linear relationship between the amplitude of the coda wave and the change in stress.(3)Study the stability,repeatability and reproducibility of the data and its results.The continuous test of the no-load state of the concrete I-beam was carried out,and the change of the waveform energy during the day was investigated.The influence of the coupling agent and the instrument temperature on the stability of the test waveform energy was found.On the basis of repeated cyclic loading and unloading tests,the repeatability of eigenvectors between data groups is investigated.It is found that the eigenvectors between groups shift downwards with the increase of the number of cyclic loading groups.By excluding the influence of memory mats and inter-group characteristics The vector offset decreases as the maximum load level decreases,verifying that the concrete has a memory for the maximum load history.After eliminating the influence of concrete loading memory and loading position micromotion on the test results,after repeated rigorous repeated tests for many days,it was found that the temperature and humidity changes of the environment had a significant influence on the eigenvector shift.