Multi-objective Optimization and Experimental Validation of a Drive Neutral Equilibrium Mechanism for Active Structural Control

Active structural control systems offer potential improvements in the serviceability of dynamically sensitive bridges. This study experimentally evaluates a Direct-Drive Neutral Equilibrium Mechanism (DNEM) for precision displacement control of a 2.5 m laboratory-scale steel bridge under dynamic loading. The system integrates a rotary-arm-and-tendon actuation mechanism with a composite real-time control strategy (proportional-derivative feedback and harmonic compensation). The 1,000 Hz closed-loop control relies exclusively on LVDT measurements for real-time precision feedback, while a Digital Image Correlation (DIC) system (500 fps) is employed in parallel solely for offline independent spatial validation. Controller gains were optimized using NSGA-II (Kp=42.3 N/mm, Kd=3.7 N·s/mm) within a fixed structural configuration. Experimental results demonstrate a 99.2 % peak displacement reduction under impact loading (6.00–0.05 mm) and steady-state cyclic precision of 0.128±0.0076 mm under a sustained 5 kN moving load. Phase-portrait analysis confirmed stable closed-loop operation without limit-cycle behavior. The close agreement between LVDT and DIC measurements validates the experimental methodology. This study establishes quantitative performance benchmarks for controller tuning, actuator evaluation, and future full-scale implementation of active bridge control technologies.