Abstract Summary
In this study, the adverse effect of an inadequately designed input control force is investigated in exciting the torsional modes of a structural system. The initial formulation is developed based on a generalized symmetric structural system under control input that is designed to regulate only the lateral modes of the system. The system is perturbed by considering an assumed eccentricity that may occur due to the change in the system stiffness. A closed-form expression of the control spillover to the torsional modes of the system is generated considering the first-order perturbation approach. The proposed closed-form expression is verified through a numerical example of a single-story three-dimensional symmetric frame structure with a rigid diaphragm at its top. The structure is subjected to several ground excitations with dominant broadband frequencies. The initial input control is designed considering the PID control strategy to control the lateral modes of the structural system. The influence of different parameters, namely, the stiffness degradation, Eigenvalue spacing, and the absolute natural frequencies are studied in the context of torsional spillover phenomena. In the last part of the study, an experimental investigation is performed on a frame, which is a scaled down model of the structure considered during the numerical study. An input force considering the PID control mechanism is fed back using an Arduino data acquisition system. Sinusoidal excitations with different frequency ratios and white noise excitations are considered as the input during the experiment.
