Research On Void Detection Of Concrete Filled Steel Tubular Arch Bridge Based On Eddy Current Thermal Imaging

Since 1990,concrete-filled steel tube arch bridge has become one of the preferred bridges for long-span bridges in mountainous areas and river-crossing bridges in cities because of its high stiffness,good bearing potential and high safety performance.After years of development,the number of long-span concrete filled steel tube arch bridges in China has ranked first in the world.However,due to the imperfect construction technology,large temperature variation and concrete shrinkage and creep,the void problem of concrete filled steel tube arch bridge is still one of the persistent problems of the bridge type.How to scientifically and objectively grasp the void situation of concrete filled steel tubular arch bridge and adopt pertinent maintenance measures is a hot topic in bridge engineering and academia.At present,although many concrete filled steel tube(CFST)void detection technologies can qualitatively evaluate the void disease,it is difficult to quickly and quantitatively detect the void disease,which brings security concerns to the operation and maintenance of bridges.Therefore,it is urgent to find a method that can quantitatively detect the void disease of concrete filled steel tube arch bridge.Based on the analysis of the principle of Infrared Thermal Imaging Nondestructive testing,this paper studies the technology of infrared thermal imaging to detect the void of concrete filled steel tube arch bridge by combining theoretical research,experimental analysis,finite element simulation and image processing.The main research contents and conclusions are as follows:(1)On the basis of combing and analyzing the research progress of void detection technology,pulse eddy current thermal imaging technology and infrared thermal imaging processing technology of concrete filled steel tube arch bridge,a new non-destructive testing method for void disease of concrete filled steel tube arch bridge using infrared thermal imaging technology is proposed,and the relevant theory of infrared thermal imaging technology driven by infrared heat source is expounded.(2)Infrared testing of concrete filled steel tubular void based on radiation heat source and eddy flu was carried out.Based on the infrared detection test of concrete filled steel tubular(CFST)void by radiation heat source,the temperature distribution on the surface of CFST specimens under the conditions of sunshine heating and temperature simulation test box heating is studied,and the validity of locating the void of CFST by infrared thermal imaging principle is verified.Based on the infrared detection test of CFST void caused by eddy flu,a new method is proposed.The influence of void thickness,steel tube wall thickness and coil lift-off height on the surface temperature rise rate of concrete filled steel tube was obtained by using the test method of swirl flu heating concrete filled steel tube specimens rapidly.The sensitivity analysis of the influencing factors was carried out by using multiple linear regression analysis method,which provided data basis for the quantitative study of void thickness.(3)Finite element simulation analysis was carried out to simulate the heat conduction process of concrete filled steel tube under different heat sources.The experimental results of radiation heating and eddy flu heating were verified.A three-dimensional transient heat transfer model was established to analyze and verify the temperature distribution on the surface of concrete filled steel tube and the effectiveness of infrared thermal imaging in identifying void defects.A transient heat transfer simulation model of ElectromagneticThermal coupling field was established to simulate the natural cooling process after eddy flu heating-stopping heating.The influence of different working conditions on the temperature rise rate of concrete filled steel tube surface was analyzed,and the testing parameters were improved.Finally,by comparing the experimental results with the simulation results,a quantitative method for calculating the void thickness through quantitative indicators is proposed.(4)Aiming at the problem that the contrast of thermal image is not high enough,an image enhancement method based on thermal image information reconstruction and adaptive histogram equalization with limited contrast is proposed.The signal reconstruction and image enhancement of thermal image are realized.The contrast between defective and non-defective regions of thermal image is improved by 60%,and the accurate discrimination of void position and area is realized.