Experimental Study On Damage Conditions Of The Steel-Concrete Composite Beam Based On The Bridge Surface

In order to overcome the shortcomings of the manual safety inspection,we want to find a more efficient and more accurate monitoring method.Based on the National Natural Science Foundation Project “Research on the Method of Obtaining the Bridge Deformation and Deducing the Structural State Based on the Differential Analysis of Image Contour(51778094)”,we carried out loading tests of the steel-concrete composite beam under various damage conditions,and we have studied the damage identification method based on the deformation monitoring of the bridge deck.The main research contents are as follows:The loading tests of the steel-concrete composite beam under various damage conditions were carried out,and the mobile photogrammetric track vehicle developed by our team was used to collect images of the beam.Then,we reconstructed 3D models of the beam under different damage conditions and loading conditions.Based on the moving least square method,point cloud denoising of 3D models was carried out.Based on the iterative closest point algorithm,3D models are matched.Next,we proposed a method based on "Post-Stack Difference" algorithm to obtain the three-dimensional shape changes of the deck surface.This method can separate the noise information such as the partial failure of the bridge deck,and obtain the deformation data.We also studied a method based on the deformation chromatogram to visualize the morphological changes of the spatial surface of structures.Based on the relationship between characteristic curvature and structural damage,the structural damage can be identified by the curvature mutation of the deflection curve of the beam.Then,we used the curvature calculation method of discrete points based on chord to calculate and analyze the curvature of the point cloud data of four damage states.Next,a wavelet denoising algorithm based on improved threshold function is proposed.This algorithm makes the threshold function continuous at the threshold ?,and avoids the constant deviation between the wavelet coefficients of the processed signal and the wavelet coefficients of the original signal.The results show that the damage of vertical abdominal rods can form stable low frequency signals in the 3D models,and the change of curvature near the damage rod is more remarkable.This finding verified the relationship between characteristic curvature and structural damage which is derived in this paper.The use of the curvature calculation method of discrete points based on chord and the wavelet denoising algorithm based on improved threshold function can eliminate the high frequency noise of the original curvature signal and identify the low frequency signal of the damage.According to the processed curvature curve,the degree and position of the damage of the vertical abdominal rods can be roughly identified.This finding verified the feasibility of the 3D point cloud damage identification method based on the curvature and the wavelet denoising.