基于NSGA-II算法的桥梁拆除方案多目标优化

Multi-Objective Optimization of Bridge Demolition Plan Based on the NSGA-II Algorithm

摘要: 针对既有桥梁拆除过程中经济成本、碳排放与施工安全难以协同优化的问题，提出一种基于NSGA-II算法的桥梁拆除方案多目标优化方法。构建以桥梁拆除总成本、碳排放量和综合风险指数为目标函数、以拆除全过程最小可靠度指标为安全约束的多目标优化模型，采用NSGA-II算法进行求解，获得满足安全底线的Pareto最优解集。以一座带挂梁预应力T构桥为工程对象，对钢筋混凝土结构采取切割、人工/机械及静态爆破拆除三类方案进行优化比较。结果表明：成本、碳排放与风险之间存在显著冲突，难以通过单一方案同时实现最优；在可靠度约束条件下，钢筋混凝土切割拆除更易形成低风险、成本可控、碳排适中的可行解带。推荐方案总成本为176.22万元，碳排放为128.48 tCO₂，综合风险指数为4.9，最小可靠度指标为4.21，满足安全控制要求。该方法可为桥梁拆除方案比选提供量化、可比和可追溯的决策依据。

Abstract: To address the difficulty of synergistically optimizing economic cost, carbon emissions, and construction safety during the demolition of existing bridges, a multi-objective optimization method for bridge demolition schemes based on the NSGA-II algorithm is proposed. A multi-objective optimization model is established, incorporating total cost, carbon emissions, and a comprehensive risk index as objective functions, and employing the minimum reliability index throughout the demolition process as a safety constraint. The model is solved using NSGA-II to obtain a Pareto optimal solution set that satisfies the safety requirements. Taking a prestressed T-frame bridge with suspended spans as a case study, three types of demolition schemes—reinforced concrete cutting demolition, manual/mechanical demolition, and static blasting demolition—are optimized and compared. The results indicate significant trade-offs among cost, carbon emissions, and risk, making it impossible to achieve optimality simultaneously with any single scheme. Under the reliability constraints, the reinforced concrete cutting demolition method is more likely to yield a feasible solution zone characterized by low risk, controllable cost, and moderate carbon emissions. The recommended scheme has a total cost of 1.7622 million yuan, carbon emissions of 128.48 tCO₂, a comprehensive risk index of 4.9, and a minimum reliability index of 4.21, all meeting safety control requirements. This method can provide a quantitative, comparable, and traceable decision-making basis for the comparison and selection of bridge demolition schemes.