Vision-based fatigue crack detection using global motion compensation and video feature tracking

Fatigue cracks that develop in civil infrastructure such as steel bridges due to repetitive loads pose a major threat to structural integrity.Despite being the most common practice for fatigue crack detection,human visual inspection is known to be labor intensive,time-consuming,and prone to error.In this study,a computer vision-based fatigue crack detection approach using a short video recorded under live loads by a moving consumer-grade camera is presented.The method detects fatigue crack by tracking surface motion and identifies the differential motion pattern caused by opening and closing of the fatigue crack.However,the global motion introduced by a moving camera in the recorded video is typically far greater than the actual motion associated with fatigue crack opening/closing,leading to false detection results.To overcome the challenge,global motion compensation(GMC)techniques are introduced to compensate for camera-induced movement.In particular,hierarchical model-based motion estimation is adopted for 2D videos with simple geometry and a new method is developed by extending the bundled camera paths approach for 3D videos with complex geometry.The proposed methodology is validated using two laboratory test setups for both in-plane and out-of-plane fatigue cracks.The results confirm the importance of motion compensation for both 2D and 3D videos and demonstrate the effectiveness of the proposed GMC methods as well as the subsequent crack detection algorithm.

冲刷作用下砂土地层中桩的侧向力学性质分析

[目的]冲刷是在水流以及波浪作用下土体流失的一个过程,它通常发生在桥梁、港口码头、以及海岸平台等结构的基础周围,造成基础的承载力下降,危及上部结构的安全。目前在分析桩的侧向力学行为时,只考虑了冲刷深度对桩的侧向承载力的影响,而忽略了冲刷形成的冲刷孔的影响。事实上,冲刷孔的几何形状不仅包括冲刷深度、还包括了冲刷孔的宽度以及冲刷孔的坡度。目前,工程设计中广泛采用的侧向桩分析方法,即p-y曲线方法无法考虑冲刷孔三维几何形状对桩的侧向力学性质的影响。[方法]针对这个问题,文章提出了一种修正的p-y曲线方法以用于分析砂土地层中桩在冲刷作用下的侧向力学响应。[结果]该方法改进了基于锲形体破坏模型的Reese p-y曲线法,从而能考虑冲刷孔三维几何形状的影响。将计算得到的结果与三维有限差分数值分析的结果进行了比较,验证该修正方法的可靠性。[结论]计算结果表明:在冲刷孔的几何形状参数里,冲刷深度对桩的侧向力学性质的影响最大,其次是冲刷孔的宽度与坡度。忽略冲刷孔几何形状的影响,桩在地面位置的侧向位移会增加49%~68%。