Application Of Computational Vision In Quasi-static Test Of Full-scale Concrete Columns With Variable Axial Force

Digital speckle correlation method has been widely used in measuring deformation information of the surface of the engineering members,including displacement,strain,frequency,etc.,due to its advantages of simple optical path,noncontact,convenient operation and low cost.The use of digital speckle correlation method to measure the deformation information of engineering members can enrich the means and contents of the test,and allow researchers to have a more comprehensive understanding of the failure form and mechanism of the engineering members,which has certain theoretical research significance and engineering practical value for the design and optimization of engineering members.In this thesis,the identification of crack,displacement fields and strain fields based on digital speckle correlation method is studied and applied to the identification of crack,displacement fields and strain fields of full-scale reinforced concrete columns with variable axial force in quasi-static tests.The research contents are as follows:（1）Two strain field error suppression algorithms are proposed,which both the error probability density function and the exponential weight function constructed are based on the single point redundant strain information.Two strain field error suppression algorithms are respectively used in the pointwise least squares method to identify the strain field of the computed-simulated speckle images test,the tensile test of a plate with one hole and the bending test of a reinforced concrete column with cracks.The identification results are compared with those of the pointwise least square method without noise suppression and the regularization-aided finite element strain calculation method.The results show that the proposed algorithm in this thesis can improve the calculation accuracy of the strain field and greatly improve the calculation efficiency.The strain field can be identified with a small calculation window with the same accuracy,so that the digital speckle correlation method can be suitable for multiple boundaries and broaden it.Comparing the two strain field error suppression algorithms proposed in this thesis,the exponential weight function noise suppression algorithm is more efficient.（2）Based on the method of combination of the peak value and the threshold value of principal tensile strain,the crack coordinate and shape are extracted.This method is applied to the computed-simulated speckle images test and full-scale reinforced concrete column test with cracks,and the results are in good agreement with the experimental results.The results show that this method can effectively identify the shape and location of fractures,and can identify micro cracks effectively.（3）The visual data from the pseudo-static test of full-scale reinforced concrete columns with variable axial force are sampled,and the shape and width of cracks in plastic hinge region of reinforced concrete columns are identified;The displacement field is identified,and the displacement field and the cross-section displacement distribution of the crack region and the non-crack region are extracted;the Green strain and the principal tensile strain and the principal compressive strain vector based on the image plane are identified,and the cross-sectional Green strain distribution of the crack region and non-crack region is extracted.