Evaluation Of Concrete Structure Integrality Based On Infrared Imaging

The research of this paper is supported by NSFC key project(50238040) and NSFC(10672128).Owing to the complexity of the failure of concrete and its structures, and the indeterminacy of the engineering structures, synthetically considering the safety and economy, the problem of design, quality, application and maintenance appears successively in the different phases of the life cycle of the engineering structures designed on the base of reliability. Much attention focused on the state survey, intensity assessment, crack evaluation, life-span forecast, health monitoring and risk management of existing concrete structures in recent years. Aimed at the integrity assessment of concrete structures, focused on the heat transfer -damage coupling, by means of IR Imaging technology, damage mechanics and theory of fractal, this thesis carries on systemic research on defect evolution of concrete and the degree of its effect together with the interrelation to the weakening of thermal conductivity and the cumulation of the damage from three aspects including theories, experiments and fractal. The study's main findings and conclusions are as follows:(1) Development of concrete structure integrity assessment problem and method with damage field description of integrity assessment. Based on the summarization and establishment of attribution model for accidents, failure model for materials and damage mechanism of concrete, the viewpoint that structure integrity problem is to research on the defect evolution and the degree of its effects on fixed performance and prescriptive function is put forward. Damage field is appropriate to describing and evaluating concrete integrity because it acts as chaos evolvement of the micro-cracks and weakening of its capability.(2) Establishment of theoretical model of heat transfer -damage coupling for concrete. The exterior temperature field with and without crack are quantificationally analysed. The result shows that temperature field is the function of the thermal conductivity, which is the theoretical base of describing and characterizing the damage field with the IR Imaging temperature field. The chaotic evolution of concrete damage is quantificationally expressed, which establishes the foundation of describing and characterizing the IR Imaging temperature field. So the connotation of concrete heat conducting -damage coupling is sublimed.(3) Pick-up of the characterizing factors based on the IR images of concrete fractal damage. This study focuses on the exterior temperature field(IR Imaging method) acquisition corresponding to different damage field and pick-up of characterizing factors(fractal dimension method). The first one mainly includes problems of the heating source, imaging and the swatches, i.e. experimental research on heat conducting -damage coupling; the second one mainly includes description, calculation and analysis of fractal dimension, i.e. fractal dimension research on heat conducting -damage coupling.(4) Establishment of integrity assessment system based on the fractal dimensions of concrete structures. The integrity of concrete structures is described by the field, the damage field is represented by the temperature field, the temperature field is indicated by the IR image, and the IR image is characterized by the fractal dimensions. The integrity assessment criterion based on the fractal dimensions and damage characterizing factors of concrete structures is proposed, and a integrity assessment system is formed. By means of the theoretical, experimental and fractal dimension research on heat transfer -damage coupling for the concrete structures, it is concluded that the different temperature fields picked up by IR imaging technology corresponds to different damage fields, and act as different IR images. the fractal dimension calculations and analysis are done for these images, the result shows that with the enhance of the damage, single fractal dimensions rise first slowly and then rapidly, while mutifractal eigenvalue first rises and then decreases. Based on this conclusion, further definition of damage variables is gained and total difference method and increment ratio method for concrete structure assessment are proposed.This research is of important significance on the integrity assessment of concrete structures, and some promotion to the application of non-destructive testing.