Numerical Simulation Study On The Detection Of Wall Defects Of The Concretefilled Steel Tubes Based On The Infrared Thermal Imaging Technology

With the development of high-rise buildings and super high-rise buildings,concretefilled steel tubes with high bearing capacity,good anti-seismic performance,convenient construction and environmental protection economy are used more and more widely in the construction industry as the main bearing system of high-rise building.Due to the concrete in the steel tube is in a hidden state,its quality can not be visually detected.Therefore,effective detection of the quality of concrete is significant to ensure the working perfomance of the concrete-filled steel tubular members and security the safety performance of engineering structure in the practical engineering.However,artificial percussion,ultrasonic method and shock echo method used widely at present can not solve the contradiction between safety and economy in engineering application.Infrared thermal imaging technology is a non-destructive detection method that is simple and rapid.And the existing experimental study shows that the primary technique for detecting the compactness of concrete filled steel tubular column wall hollowing defects is feasible in the condition of a certain wall thickness,but its needs more further study.In this paper,the theory of infrared thermal imaging technology and conduction of concrete-filled steel tubes are introduced;and based on the existing theoretical and experimental research,the conduction process of concrete-filled steel tubes with wall defects on the conditions of hydration heat and external thermal excitation are simulated,the feasibility of detecting defects by infrared thermal imaging technology is discussed,then the effects of self factors such as wall thickness,defect size,defect depth of defects and external factors such as environmental temperature,convective heat transfer,external thermal excitation intensity and time are analyzed;some of the results are compared with the existing theoretical and experimental results.The main conclusions are obtained as follows:(1)The temperature difference caused by defects on the condition of hydration heat is too low to be identified by the thermal infrared imager,so it is infeasible to detect defects by infrared thermal imaging technology on this occasion;to achieve the purpose,methods such as external heat source are necessary.(2)On the condition of external thermal,the surface temperature on the defect area is higher than other areas,and the difference is enough to be identified by the thermal infrared imager,so it is feasible to detect defects by infrared thermal imaging technology on this occasion;and the tempereture difference increases as heating,but it decreases rapidly when heating is completed.So it is suggested to detect at the end of heating phase.(3)Wall thickness is the key factor affecting the infrared thermal imaging,with the increase of the thickness,the temperature differece between defect area and non defective area on tube surface decreases rapidly,the area of the existence of temperature difference also shrinks;defect size is an important factor,with the increase of defect size,the temperature differece between defect area and non defective area on tube surface increases;effect of defect thickness on the infrared thermal imaging is almost negligible,with the increase of the defect thickness,the temperature differece between defect area and non defective area on tube surface changes little;so it is feasible to detect the debonding defect between tube and concrete by infrared thermal imaging technology too.(4)The wall defects in the inner corner of the reinforcing ring and the steel pipe wall can also be detected by infrared thermography,though it is more difficult than normal;the thickness and width of the inner reinforcement ring will not affect the local temperature difference caused by the wall defects.(5)The environmental temperature does not affect the surface temperature distribution during the heating and heat dissipation process,the convective heat transfer coefficient does not affect the surface temperature distribution during heating process,but will lead the temperature difference between the defect surface and the non defective surface to decrease faster during the heat dissipation process.(6)The magnitude and time of the heating flow on the tube surface are important factors on the temperature difference and the detection results,the influence of heat flow intensity magnitude is approximately proportional,but the influence of thermal excitation time is not proportional,and the temperature difference increases more and more slowly as heating.