Modal Analysis Based Stress Estimation for Structural Elements Subjected to Operational Dynamic Loadings

The calculation of dynamic stresses plays a crucial role in the fatigue design and fatigue life prediction of structures. However, the uncertainty in the structural dynamic properties, i.e., stiffness, mass and damping, as well as the necessary use of simplified loading models, are the main sources of uncertainty in fatigue. In this work, a procedure for estimating dynamic stresses is proposed based on the real responses of the structure under dynamic loadings and the modal parameters of the structure, i.e., natural frequencies, damping ratios and mode shapes. The proposed methodology was validated by experimental tests in a simply-supported glass beam and a rectangular glass plate pinned-supported at three corners, both subject to dynamic random loads. The estimated stresses are compared with those measured with strain gages attached to some points of the structures. The estimated stresses are in good agreement with those provided by the strain gages which demonstrates that the methodology can be used to estimate more accurate stress time-histories.