Multi-objective optimization of direct-drive neutral equilibrium mechanism for disaster relief bridges using NSGA-II

Emergency relief bridges are critical lifelines in post-disaster scenarios but often suffer from excessive vibration and deformation due to their lightweight design. Conventional active control systems require high energy input. Passive systems lack adaptability. To address these challenges, this study proposes a novel Direct-Drive Neutral Equilibrium Mechanism (DNEM), which leverages geometric nonlinearity to create a “virtual pier” effect, achieving high stiffness with minimal energy consumption. Recognizing the conflicting objectives of minimizing structural displacement and reducing actuation energy, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was employed to optimize the geometric and control parameters of the mechanism. A numerical simulation platform representing a scaled emergency bridge was established to validate the system’s performance under moving loads. The results demonstrate that the optimized DNEM system operates under a “Zero Power Force Control” (ZPFC) regime, where most of the supporting force is generated through the redistribution of geometric potential energy. Under a 150 N dynamic load—equivalent to approximately 1.5 tons on a prototype bridge with a geometric scaling factor of λ = 10 —the system limits the mid-span displacement to 1.77 mm while consuming only 0.59 kJ of energy. Furthermore, phase-plane analysis confirmed the system’s asymptotic stability and ability to eliminate residual vibrations rapidly without overshoot. This study confirms that the AI-optimized DNEM provides a robust, energy-efficient solution for the micro-deformation control of temporary civil structures.