| Steel structures are made up of multiple structural steel members connected to each other.In modern buildings,steel structures are widely used in almost all types of building structures,including high-rise buildings,infrastructure,bridges,iron towers,airport terminals,industrial buildings.The advantages of steel structure are high strength,light weight,good overall stiffness and strong deformation ability.However,the steel structure is easy to corrode,which not only causes a lot of economic losses,but also directly affects the safety of the structure.Its quality and service life have attracted widespread attention.Coating properties,construction quality and environment factors could lead surface corrosion of steel structures.The thermal conductivity properties of the rust layer and surrounding materials are different to a certain extent.Studying the thermal conductivity properties and infrared thermal imaging characteristics of the rust layer on the surface of the steel structure can provide accurate and rapid detection of the corrosion of the steel structure under the coating by using the infrared thermal imaging.The dissertation analyses the thermal conductivity characteristics of the steel structure,the anti-corrosion coating and the rust layer,and the surface infrared thermal image characteristics of the steel structure under the condition of surface rust and coating-defect.Simulated the surface temperature field of the steel structure with ANSYS Workbench,and the internal relationship between different defects of the steel structure and the surface infrared thermal image characteristics is analyzed;physical models are made and measured in indoor and outdoor environments;summarized the temperature anomaly law of surface corrosion and coating defect steel structure.Numerical simulation and physical model analysis show that the bare steel with rust defects on the surface presents "hot spots" in the heating stage and "cold spots" in the heat dissipation stage;In the case of coating,the defects are filled with air and rust.In the heating stage,the defect parts appear as "hot spots",in the heat dissipation stage,the defect parts appear as "cold spots",and when the defects are filled with water,the defect parts appear as "hot spots".It is difficult to observe the abnormal temperature;the filling air in the defect has the greatest influence on the infrared thermal image characteristics of the steel structure surface,followed by the filling rust,and the filling water is relatively the smallest;the size and occurrence time of the maximum temperature difference in the surface temperature are related to the thermal conductivity of defects,which are air,rust and water from large to small and from early to late;the size of the thermal excitation source is positively correlated with the surface temperature difference,unrelated to the moment of the maximum temperature difference;the larger the surface area of the air defect,the larger the "hot spot" of the surface temperature field.The number of defects corresponds to the abnormal point of the surface temperature field;various defect shapes can be clearly reflected by the surface temperature field.The larger the temperature difference between the defective part and the normal part,the outcome will be better observed with the thermal imaging camera.In the middle of February in central China,when the temperature is 10-18,wind force level 2 and solar illumination is used as the excitation heat source,the optimal observation window of the three defects is from12:00 to 13:20.When indoor artificial heat source with LED lights is excited,it needs to be heated for a period of time before entering the optimal observation window.The length of heating time depends on the intensity of heat source and the thermal conductivity of materials.Bare steel with corrosion defects on the surface enters the optimum observation window faster than coated steel structure. |
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