Application Of DIC Technology In Quasi-Static Test Of Reinforced Concrete Full-Scale Columns

Digital image correlation technology is an optical measurement method commonly used in engineering,which has the advantages of non-contact,high precision,simple operation,full-field measurement and so on.It can directly obtain the deformation field of the surface of the structure and is often used in geotechnical,structural,bridge and other civil engineering fields in recent years.By measuring the displacement field and strain field on the surface of the object,this technology can more comprehensively understand the deformation characteristics,and it provides more comprehensive information for engineering test research and deformation monitoring of actual engineering structures.In this paper,the displacement and strain measurement method of digital image correlation technology is studied,and it is applied to the quasi-static tests of full-scale reinforced concrete column(RC column),and the cracks and deformation properties of fixed axial force column and variable axial force column are studied.The main research methods and conclusions are as follows:(1)The strain measurement method of pointwise moving least square fitting is proposed,which applied to simulation experiments,continuous high-gradient deformation tests,and the accuracy,computational efficiency and stability of the proposed method are compared with the classical pointwise least squares and moving least squares methods.The results show that the pointwise moving least squares method can effectively improve the computational efficiency of pointwise least squares method,and it is less affected by window size.For the case of large windows and high gradient deformation,the method has higher accuracy and lower window sensitivity.This method effectively improves the computational efficiency and approximate stability of traditional moving least square method.The visibility criterion is adopted to improve the proposed method and the pointwise least square method and is applied to discontinuous displacement field and crack test.The results show that the visibility criterion can be applied to discontinuous condition and reliable strain field can be obtained.(2)Digital image correlation technology is applied to analyze the biaxial loading quasi-static tests of full RC columns with fixed axial force column and variable axial force,and the variation frequency of axial force of variable axial force column is three times of the horizontal displacement.By calculating the principal tensile strain,the crack point,development law and distribution of microcracks at the root of the two columns in the early stage of failure are studied.And the cracks width and length of the two specimens under different horizontal displacement amplitudes are compared to study and discuss the influence of axial force changes on the development of cracks.The research shows that this technology can accurately identify microcracks.The variation of axial force results in obvious asymmetry of crack distribution,which inhibits the development of transverse cracks and affects the cracking point of cracks.Under the influence of axial force variation,the crack width of columns with variable axial force is larger under the same displacement,and it is related to the amplitude of axial force variation,but has little influence on the crack length.(3)The displacement field and strain field of fixed axial force column and variable axial force column are identified,and the variation performance of the two columns is compared and analyzed.The displacement and Green strain distributions of the sections with cracks and without cracks are extracted.The error sources of strain field in the test are analyzed,and the influence of axial force variation on deformation performance is studied by comparing the displacement field and strain field of two columns.The research shows that the deformation field is asymmetrical and the deformation is larger due to the variation of axial force.