The Research And Detection On The Density Defects Of The Concrete-filled Steel Tubes Based On The Infrared Thermal Imaging Technology

At present,a number of super high-rise buildings are under the construction.The concrete-filled steel tube column has many advantages such as the high strength,large plastic deformation,good seismic performance and convenient construction,which leads to the result that they are widely used in super high-rise buildings as the vertical load-bearing system.However, we can’t visually inspect the quality of the concrete poured into the steel tube under the construction.Therefore,timely and accurate detection is an urgent need besides the careful design and construction.In recent years,the research about the quality detection has got some progress.But it’s not enough.We still have not found a fast,convenient and effective method to detect and evaluate the density defects of the Concrete-filled steel tubes yet.Thus, developing a new detection technique used in the detection and evaluation of the inner quality of the Concrete-filled steel tubes is a must.The infrared thermography technology has been widely used in the field of the building detection because of its convenient, efficient, economical and practical characteristics.But in terms of the hollowing defects of concrete-filled steel tube at the tube wall, the quality detection research is still blank. Therefore, in this paper, we try to use the infrared thermal imaging technology to do the research.First of all, we need to study the basic theory including objects’ heat radiation, the infrared thermal imaging mechanism and the heat transfer characteristics of the hollowing defects of concrete-filled steel tube at the tube wall, which can theoretically explain and deduce the feasibility of infrared detection.And it also provides the corresponding scientific theory evidence.Subsequently, as for the concrete-filled steel tube column model specimen with the hollowing defects at the tube wall, we do the infrared test in the laboratory to explore whether it is feasible. If so, further analysis will be done.They include three aspects: tube wall thickness, defects’ thickness and surface area changes.We discuss and analyse their effects on the infrared detection results when they change.And at the same time, the defect depth theory formula is verified and modified through the experiment datas. Finally, based on the practical engineering hefei binhushidai square, the feasibility of infrared detection technology is discussed.Through the analysis of the theoretical and experimental research, the results show that using the infrared thermal imaging technology to detect the the density hollowing defects of concrete-filled steel tube at the tube wall is feasible. In addition, some quantification conclusions are obtained as follows.(1)When the tube wall thickness is less than 10 mm, this method is feasible whether heated or not.It can accurately reflect the defects’ location, shape and size.And besides, when the tube wall thickness is smaller, the critical temperature difference is bigger.Thus, defects’ outline are more clearly reflected in the thermal image, the effect of the detection identification is better. When the tube wall thickness is more than 10 mm, this method is feasible only when heated.And it can just reflect the defects’ position and outline roughly.But it can also be used for the preliminary judgment of the defects. It still has engineering application value.(2)When the tube wall thickness is less than 10 mm, with the increasing of the defects’ thickness or surface area, the temperature and the temperature difference of the tube wall corresponding to the defects will also go up.And the increasing degree will become bigger when heated.When the tube wall thickness is more than 10 mm, with the increasing of the defects’ thickness or surface area, the temperature and the temperature difference of the tube wall corresponding to the defects will also go up only when heated.This experiment result indicates that the change of the defects’ thickness or surface area has much less effect on the temperature and the temperature difference of the tube wall corresponding to the defects than the change of the tube wall thickness, which simultaneously shows that the change of the defects’ thickness or surface area will not decide whether the infrared detection is feasible or not.And according to the test results, it shows that the defect can be detected at the minimum recognition accuracy.The minimum recognition accuracy of the surface area is 4cm2 and the minimum recognition accuracy of the thickness is 1cm.(3)After heated 1 min, the calculated value and the actual value of the defect depth are in good agreement, which can also meet the engineering demand.We can combine the calculated theoretical depth with thermal image defect size to reflect the 3D location of defects in the concrete-filled steel tube.And we can control the pouring quality according to the 3D location information timely and accurately, which has certain engineering application value.Simutaneously, the solar radiation heating is more uniform.So the calculation accuracy is higher than artificially heated...