Whole Process Measurement For Structural Deformations Based On DIC

To monitor the deformation of structures in civil engineering, the whole process of structural deformation measurement based on DIC method is proposed in this paper. Zhang Zhengyou’s camera calibration method is introduced in the traditional DIC method, and the deformation measurement method for structures with single camera is described. To monitor the deflection of bridges long-term, a measurement method for bridge deflection based on CCD is proposed. Researches on how to improve the existing binocular stereo vision measurement method are done in this paper. Experimental researches are done.The main contents are as follows:(1) DIC method based on Zhang Zhengyou’s camera calibration is proposed. Lens distortion is out of consideration in traditional DIC method, which affects the accuracy. To change the unit from pixel to millimeter, a marker whose length is known before has to pasted on the surface of the specimen in advance. And this method is complicated to operate. After introducing Zhang Zhengyou’s camera calibration method to traditional DIC method, accuracy is improved, and the marker pasted on the surface becomes uneccesary, which simplifies the operation. To test and verify this method, the horizontal movement of the specimen is measured.(2) A measurement method for bridge deflection based on CCD is proposed. This method is to meet the demand of long-term monitoring beidge deflection. Special target is placed in the middle of the bridge span. And the CCD gets images including the target. DIC method is used to track the positions of the target in the images, and the deflection can be calculated from the changes of the positions. To monitor the deflection of Songjiazhuang rail-cum-highway interchange, the measurement system for the bridge is intergrated. The returned data show the system works well, and the method proposed in this paper can meet the demand of bridge monitoring.(3) Researches on improving the accuracy of binocular stereo vision system. In the process of initial stereo matching and timing matching, a method for correcting the results based on epipolar constraint is proposed. The initial results are replaced by the points nearest to the initial results and consistent with epipolar constraint. SUSAN filtering method is used in image processing. Quadratic surface fitting and cubic surface fitting are compared in sub-pixel loacation. Displacement field is projected to two orthogonal vectors which are from the fitting plane at the initial time. Two strain calculation methods are compared: least squares polynomial fitting and finite element method.(4) Experimental researches: system zero drift test, CFRP-concrete interface bond slip test, and long-span transmission model wind tunnel test. Calculate the displacement of the standing specimen, and the accuracy of the system is 0.01 mm at 95% probility. In CFRP-concrete interface bond slip test, top displacement is calculated by this method, and the results are compared to data from LVDTs. The comparing results show that the two curves have good agreement, which verifies the method in this paper is reliable and practicable. The slips of CFRP-concrete are calculated by the method. The out-plane displacement of long-span transmission model is obtained by the method.