The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine, as one of the results of fluid and structure interactions in stirred vessels, was measured using a moment sensor equipped with digital telemetry. An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment, which indicates the elasticity nature of shaft material against bending deformation, follows the Weibull distribution. The trends of amplitude mean, standard deviation and peak deviation characteristics manifest an "S" shape versus gas flow. The "S" trend of the relative mean bending moment over gas flow rate, depending on the flow regime in gas-liquid stirred vessels, resulted from the competition among the nonuniformity of bubbly flow around the impeller, the formation of gas cavities behind the blades, and the gas direct impact on the impeller when gas is introduced. A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident. The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime. (C) 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.