Dynamic Deflection Estimation Of Beam Bridges Based On Dynamic Strain

The bridge deflection, as a description of structural deformation, can be used to evaluate the quality and condition of bridges, and reflect the stiffness of bridges. Especially for the dynamic deflection, it is the most real-time reflection of bridge deformation with the influence of forces. Thus, it has important significant to monitor the dynamic deflection in Bridge Health Monitoring. In recent years, the methods based on strain testing to estimate the bridge deflection have been widely concerned and researched. For the estimation principle, the methods are mainly based on average curvature, least square curve fitting, and conjugate beam. These methods have been applied in the monitoring of static deflection in some practical bridges. But for the monitoring of dynamic deflection, due to these methods only takes the static strain-displacement relationship into consideration, and with ignoring the influence of bridge vibration, these methods are difficult to estimate the dynamic deflection in a high accuracy.For beam bridge, this thesis presents a new technique to estimate the dynamic deflection based on strain modes. The strain mode shapes are first estimated from the cross-correlation function of the measured dynamic strain data. Then, the displacement mode shapes can be estimated from the strain mode shapes based on the displacement-strain relation. With knowing the strain mode shapes and strain data, the corresponding modal coordinates can be estimated. The dynamic deflection can then be estimated by the obtained displacement mode shapes and modal coordinates. The method is verified by numerical simulations of a simply support beam and a continuous beam subjected to impulsive excitation, earthquake excitation and moving load. Experimental tests of a simply supported beam under various hammering excitations are also conducted to verify the effectiveness of the proposed method. For the dynamic deflection under moving load, the presented method can also be used to estimate, combined with the analytical mode decomposition theory. Both the numerical and test results show that the proposed method can estimate the dynamic deflection of bridges with a high accuracy.