The bending moment acting on an overhung shaft equipped with an unbalanced impeller, as one of the results of the lateral Fluid-Structure Interactions (FSI) in stirred vessels, was measured using a moment sensor, equipped with digital telemetry. The results show that the imbalance of impeller has a considerable influence on the characteristics of bending moment, such as the mean amplitude and the intensity of amplitude fluctuation. Analysis of the amplitude distribution shows that the distribution is well fitted by a Weibull distribution, which tends to flatten and become more symmetrical about the mean as the imbalance increases. Further analysis of the bending moment power spectral density shows that the speed frequency of the bending moment, whose contribution to the bending moment fluctuation increases with the increasing imbalance, is caused by the imbalance of the stirring structure. These results can be applied to the mechanical design process for the shaft and the stirred vessel supporting it, and the manufacturing control of impeller balance quality. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.