Free‐rocking tests of a freestanding object with variation of center of gravity

Abstract

AbstractFreestanding nonstructural objects are very common in various infrastructure systems, but their dynamic properties with variations in the center of gravity (CG) are not yet fully understood. To investigate the dynamic properties of a freestanding object as its CG is varied, a steel frame model was fabricated using movable steel plates. Two scenarios, with varying and fixed CG, were considered in the free rocking tests. The experimental rotation responses generally matched the analytical responses in the initial cycles, and the discrepancy increased as the height of the CG (hcg) increased. The magnitude of the quarter period exhibited a similar trend. When the CG was fixed, the resulting magnitude of the quarter period varied slightly with hcg, indicating that the CG is one of the primary parameters affecting the quarter period. When the CG was varied, the experimental energy reduction factor was generally larger than the analytical results computed using the methods suggested in the literature, and it was scattered around the fixed CG value. The magnitude of the damping ratio was also scattered as the quarter cycle number increased, and it slightly decreased as hcg increased. An equivalent rectangular rigid block model with an equivalent height (heq) was employed to compute the geometric and dynamic parameters of the steel frame. The accuracy of this measure was investigated in terms of the quarter period and energy reduction factor. This work is beneficial for understanding the rocking behavior of freestanding objects.