Crack assessment is an essential process in bridge detection. In general, most non-contact crack detection techniques are not suitable for widespread use. The reason for this is that they all need to position the ruler at the inspection site in advance or calibrate the camera unit pixel size at a certain distance in a very intricate process. However, the object distance method in this paper can complete the calculation using only the crack image and the working distance, which are provided by an acquisition system equipped with a camera and laser range finder. First, the object distance method and the scale method are compared by calculating the crack width, and the results show that the object distance method is the more accurate method. Then, a double edge pixel statistical method is proposed to calculate the crack length, which solves the problem of redundant and missing pixels. In addition, the conventional mosaic algorithm is improved to realize an image mosaic for the more efficient splicing of crack images. Finally, a series of laboratory tests were conducted to verify the proposed approach. The experiments showed that the precision of crack length extraction can reach 92%, and the improved algorithm stitching precision can reach 98%.

In spring, the river ice melts to a certain extent and cracks to form drift ice and impact force on the bridge abutments; the river ice, due to the impact of ablation, has an internal formation of different porosities, and the level of porosity affects the mechanical properties of the river ice, so that the impact force generated by the river ice is also different. In this paper, the Heihe–Blagoveshchensk Amur River Bridge abutment is the object of river ice impact, and the discrete element method (DEM) is employed to analyze the impact process and impact force on the abutment by numerical simulation of the melting river ice. The damage characteristics of the ice rows with different ice speeds, ice thicknesses, and porosity, and the time curve of the impact force are obtained. It is found that the maximum impact force of river ice on the abutment decreases nonlinearly with the increase in river ice porosity; the peak contact force occurs with a lag time, and the damage is gradually concentrated in the vicinity of the area in direct contact with the abutment. In this paper, according to the simulation results, the relationship between river ice porosity and the maximum impact force on the bridge abutment, as well as the time parameters, is obtained by fitting, and the power loading model of the bridge abutment impacted by the river ice is established, which provides a basis for the reasonable calculation of the impact force of the ablated river ice at bridge abutments.