Control Effect Analysis of a Bridge under Control of Neutral Equilibrium Mechanisms (NEMs) as Multiple Virtual Piers

Abstract

When natural disasters occur, real-time disaster relief operations need to be implemented. But if disaster relief transportation is interrupted, these operations will be severely hampered. Emergency relief bridges must be erected so that people, materials and machinery can reach the disaster area smoothly. Therefore, one indispensable tool of disaster relief organizations is the light bridge. The design of such a lightweight bridge is controlled by deformation, not strength, so the span of the bridge is limited. Thus, this study proposes a bridge with multiple NEMs acting as multiple virtual piers of the bridge and an active structural control method was adopted to expand the span of the light bridge. The experimental results showed that, for the maximum vertical displacements at 1/3 and 2/3 distances from the left side of the bridge under uncontrolled and controlled conditions, the displacement reduction rates of the bridge were 96.20% and 98.42% for the outbound trip and 93.32% and 98.47% for the return trip, respectively. For the displacement control at the midpoint of the bridge under uncontrolled and controlled conditions, the displacement reduction rates of the outbound and return trips were 96.77% and 96.62%, respectively. The images from the experiment also showed that the cantilever arm of each NEM could be rotated by the PID controller to the appropriate angle to provide sufficient upward force to balance the vertical displacement changes based on the position of the moving load. Thus, zero-displacement control of a bridge can be achieved, and the control effect is quite significant.