When natural disasters cause bridges to collapse, the delivery of rescue equipment and supplies to remote disaster areas is impeded and disaster relief efforts are thus delayed. In this study, to enhance and improve light bridges for disaster relief, a neutral equilibrium mechanism (NEM) is proposed to adjust the internal force of the bridge and reduce the deformation of the bridge. The NEM is installed at the center of a bridge to form a virtual bridge pier. A prototype of the NEM, composed of a pair of prestressed steel tendons, two pairs of anchor seats, a rotation cantilever arm mechanism, and a pair of radio-controlled (RC) servos, is proposed to test and verify the control effect of a bridge with the NEM. Test and analysis results show the following: (1) The rotation angle of the cantilever arm can be rotated by the RC servo to appropriate angles to provide adequate upwards resultant force to balance the moving load. (2) The vertical displacement of the bridge can be controlled to close to zero by this proposed NEM. (3) The maximum vertical displacement at the midpoint of a bridge with the NEM control mechanism can be controlled to far below 1/400 of the span of the bridge required by the design criteria. (4) A bridge under the control of an NEM under a low-speed moving load with various control gains achieves fine displacement reduction effects, but the displacement reduction effect for a high-speed moving load with low control gain decreases. Test results also show that the bearing capacity of an existing bridge with an NEM can be increased and the weight of the bridge can be reduced. The effective span of a bridge can be increased without increasing the depth of the cross section. The feasibility and practicality of applying this proposed NEM to form a virtual pier of a bridge have been verified in this study.
Cooperative control mechanism and control effect analysis of coal seam backfill mining
