To address the limitation of existing bridge maintenance optimization methods that fail to consider interactions between sequential decisions across the entire service life, this study proposes a multi-stage, two-level optimization framework grounded in sequential decision-making principles. The upper level model determines performance improvement goals for the maintenance sequence, while considering the influence of preceding decisions on subsequent maintenance policies. The lower-level model then identifies the optimal maintenance actions for each component at each stage, subject to the upper-level constraints. Case analysis shows that, while maintaining superior structural condition over the full life cycle, the proposed method reduces cumulative maintenance cost by 28.6% compared with the traditional strategies. Moreover, when the average deterioration rate of the performance condition index is below 1.425 per year, total life-cycle maintenance and rehabilitation cost can be further reduced by reducing the number of decision-making stages.

In the damage detection of composite blade, it is very important to accurately and rapidly obtain the dynamic characteristics of blade before and after blade damage. Therefore, an efficient numerical calculation method for composite blade damage simulation was proposed under the finite element framework based on the homogenization of composite materials, extended Bredt-Batho shear flow theory and damage stiffness degradation theory, and the corresponding finite element program is developed based on Python language. On this basis, the composite sandwich cantilever beam is taken as the research object and compared with ANSYS calculation results to verify the rationality of the composite material homogenization method. At the same time, it is applied to simulate the modal calculation of NREL 5MW fan blade under different damage conditions. The results show that the numerical calculation method can simulate the blade leading edge crack damage well. The blade frequency gradually decreases with the deepening of damage degree. The leading edge crack has more influence on blade flapping direction. Under the same damage degree, the frequency of blade leading edge crack decreases more as it gets closer to the root. The leading edge crack at the blade root has a great influence on the blade oscillation direction, while the leading edge crack at the blade tip has a great influence on the blade oscillation direction. The blade leading edge crack has little effect on the natural frequency, and the curvature damage factor calculated by the mode displacement of the flapping direction can be used as the damage identification index to identify the blade leading edge crack damage effectively.