Damage Identification Of Reinforced Concrete Beams Based On DIC Technology

Among the existing building structures in China,most of them have been built for years,and even new ones,have quality and safety problems.The building structure has been affected by adverse factors for a long time,such as the external environment,and the defects existing in design and construction,which may lead to structural damage and thereby influence the serviceability and safety of the structure.Some scholars at home and abroad have conducted extensive and in-depth researches on the safety and reliability of building structures.With the development of new technologies,several scholars have tried to study a long-distance,non-contact measurement method.Digital Image Correlation(DIC)method is a long-distance,contactless optical measurement technique,which is based on dynamic displacement measurements.Compared with traditional measurement methods,the technique has such advantages as simple operation,strong environmental adaptability and wide application range.So it is one of the important development directions in the field of optical measurement.Based on the research background,through the experimental research and theoretical analysis,the DIC technique based damage identification method of reinforced concrete beams has been studied in this dissertation.The main research contents and conclusions are as follows:(1)Four groups of large-sized reinforced concrete beams with different shear span ratios were designed,two in each group.In order to ensure the randomness of the gray gradient and the speckle distribution,the surface of all components is artificially painted by a speckle pattern.The quality of the speckle pattern has an important influence on the accuracy of the DIC measurement.In this paper,the production quality of speckle images in digital image-related applications are studied in depth.Different speckle particle sizes are selected for different shooting distances,different displacements and different light changes.According to the experimental research,the optimal size of the speckle pattern after imaging should be around 3-4 pixels.(2)Research on DIC measurement accuracy and applicability.In this test,three different measurement methods,DIC technique,traditional displacement meter and laser displacement,were used to measure the vertical displacement of the mid-span.The first two methods are compared with the laser displacement measurement respectively.It is found that the DIC measurement is basically consistent with the displacement curve obtained by the traditional displacement measurement,and both errors are within the acceptable range.It is verified that DIC technique has a high accuracy in the vertical displacement measurement.The DIC measurement technique is used to measure the displacement of the experimental components,and the full-span vertical displacement of the whole component under different loads is obtained.By comparing and analyzing the displacement curves obtained from the traditional displacement measurement,the limitations and instability of the traditional displacement measurement are revealed while verifying the applicability of DIC.(3)According to the relevant domestic and foreign stiffness identification theory,the damage identification equation of the bending stiffness distribution of the member under load is established by the reverse analysis program,and the identification performance of the equation is evaluated by simulating the steel beams with different induced damages.Then,the vertical displacement measured by DIC technique is used as the input value of the damage state equation to evaluate the damage of the concrete beam at different loading stages.The research results show that the established damage identification equation has a high accuracy in the stiffness identification of the beam during the loading process.The application of this technique in the health detection and identification of the structure will greatly improve the detection and identification efficiency of the structure and provide a reliable basis for the structural damage identification.