A chart to evaluate the effect of active control on a bridge

To reinforce and improve the function of a light bridge for disaster relief, a neutral equilibrium mechanism (NEM) was developed and applied for controlling the internal force and reducing the vertical deformation of a bridge to form as virtual piers. The control force of the NEM was generated by a proportional–integral–derivative controller with a combination of displacement G_P, speed G_D and adjusted G_I gain coefficients to neutralise the vertical deformation of a bridge that had been created by a moving live load and the dead weight of the bridge. To effectively evaluate the control efficiency of bridge deformation under this mechanism, a multi-dimensional quality evaluation method is proposed to assess the control benefits of bridge deformation under different combinations of control coefficients. The test and analysis results in the control performance analysis chart show clearly that the control performance index MTI_i is around 2–3, 3 and 5, respectively, for the combination of: G_P = 0.5, G_D = 0.0, G_I = 0.02; G_P = 1.0, G_D = 0.0, G_I = 0.02; and G_P = 2.0, G_D = 0.0, G_I = 0.02. The analysis results present a clear demonstration of control performance, which can serve as a reference for future practical control safety.