Experimental Study On Non-destructive Testing Technology Of Concrete Filled Steel Tube

In recent years,bridges and high-rise buildings are being constructed in large quantities.Concrete-filled steel tube structure has many advantages,such as high strength,light weight,high industrialization,convenient construction and excellent seismic performance.Therefore,it is often used as a structural form of long-span bridges and high-rise building load-bearing system.When long-span bridges adopt concrete filled steel tubular structure,construction is difficult.Even with the most advanced construction scheme,it is difficult to ensure the compactness of concrete inside steel tubular,especially in the dome area.Due to the shrinkage and creep of concrete,the steel tube wall and core concrete will also appear debonding phenomenon.These factors will reduce the mechanical properties of concrete filled steel tubular,which directly affects the safety of buildings.Therefore,it is very necessary to test the internal quality of concrete filled steel tube.The purpose of this paper is to improve the accuracy of nondestructive testing methods for concrete filled steel tubes and to explore new fast and effective testing methods.Based on the ultrasonic method,two new non-destructive testing methods,shock elastic wave vibration method and infrared thermal imaging method,are used to detect the void defect of concrete filled steel tube(CFST)model.The following work has been carried out:(1)On the basis of consulting a large number of domestic and foreign relevant literature,the research status of shock elastic wave method,ultrasonic method and infrared thermal imaging method in the field of non-destructive testing and non-destructive testing of concrete filled steel tubes are analyzed and summarized.(2)According to the experimental principle and the construction code of concrete filled steel tube,five defects with different void thickness were designed and fabricated.Three non-destructive testing methods(shock elastic wave method,ultrasonic method and infrared thermal imaging method)are used to test the test components.The results show that these non-destructive testing methods are feasible to detect the void defect of concrete filled steel tube,and can be used to evaluate the void defect of concrete filled steel tube.(3)The basic theory of elastic wave is expounded.This paper introduces the classification,reflection characteristics of elastic wave and the principle of detecting concrete filled steel tubular by shock elastic wave,and summarizes several methods of detecting concrete filled steel tubular by shock elastic wave method.The results show that the shape of the void defect of concrete filled steel tube can be effectively detected by shock elastic wave vibration method,and the void thickness can also be quantitatively detected by shock echo method.(4)The propagation law of ultrasonic wave in concrete filled steel tube is expounded,and the basis for evaluating the quality of concrete filled steel tube by ultrasonic method is summarized.It is found that the ability of ultrasonic method to detect the void defect of concrete filled steel tube can be improved by synthesizing the acoustic velocity and frequency parameters of ultrasonic wave,and the ultrasonic velocity and frequency parameters of the defect with larger void thickness change obviously.(5)Starting from infrared imaging theory and heat conduction theory,the detection methods and influencing factors of infrared thermal imaging method are summarized.The results show that the infrared thermal imaging method can detect the shape of the void area quickly and effectively.The detection effect is related to heating time and the thickness of the steel tube.That is,the bigger the void thickness is,the thinner the wall thickness of the steel tube is,and the bigger the temperature difference between the dense area and the void area is,the better the detection effect is.