Damage monitoring systems based on Lamb wave health monitoring technology have attracted considerable attention for scientific research and industrial applications. In this article, two types of single-mode Lamb waves are obtained using symmetric and anti-symmetric methods, respectively, to determine a crack identification signal. A numerical simulation of a welded steel plate model was conducted using the ABAQUS/EXPLICIT module, which is a dynamic solver. The propagation process and the corresponding effect of the Lamb waves over the complete and damaged models are simulated. According to the propagation characteristics and with the assistance of the ellipse localization method with MATLAB, the location of crack damage is simulated by the amplitude addition method and the crack damage location is determined. The results show that the simulation results are in good agreement with the actual crack damage. Furthermore, the received signals are compared and analyzed from an energy perspective. Two types of single-mode Lamb wave monitoring methods are also compared. In addition, it is demonstrated that a symmetric excitation can simplify the received waves and recognize crack damage in plates in welded steel structures from an experimental perspective of this work.

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Steel structures are widely used in large-span bridges, offshore platforms, mining equipment and other large-scale buildings. The damage of steel structures will cause significant safety risks in a project. Therefore, it is of great significance to identify and study damage to steel structures. In this study, the propagation of Lamb waves in a steel plate with double cracks is simulated. Using finite element analysis and experimental study, damage identification and damage imaging of double crack damage to a steel plate are performed, and the numerical simulation results are in good agreement with the experimental results. Considering the reflection and transmission of Lamb waves at the welding seam, the location and imaging of crack damage in a welded steel plate are also studied. The imaging results obtained from simulation and experiment show high level in accuracy. By comparing the amplitude of the signal in the propagation process, it is concluded that the transmission energy at the weld seam decreases.

Large-span spatial steel structures are subject to complex stress conditions during construction, especially during the unloading phase, and they are easily affected by the environment and the loading method. Therefore, it is necessary to analyze the influence of different unloading construction methods on the structural reliability during construction to improve the quality of construction safety. In this paper, ANSYS version 16.0 software is used to establish a finite-element analysis model of the truss structure of the Harbin railway station. The synchronous unloading process and asynchronous unloading process are numerically simulated, and the stress variation trend of the arch truss during the unloading stage is studied. The research results show that the effect of simultaneous unloading on the mechanical state of the structure is small. During the unloading process, stress is more likely to exceed its limit in the area where the boundary conditions change. Then axial strain monitoring was performed during the actual unloading process of the truss structure of the Harbin railway station. The results show that the effect of synchronous unloading on the structure's stress state is small, which is in good agreement with the numerical simulation results.

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