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

Abstract

Freestanding 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.

An Intensity Measure for the Rocking Fragility Analysis of Rigid Blocks Subjected to Floor Motions

“…As a very early study in this area, Housner [12] proposed a seminal framework to evaluate the seismic response of a solitary rigid block placed on a rigid base. Following this pioneering work, investigators over the world have endeavored to evaluate the rocking response of freestanding blocks, including experimental [13][14][15][16][17][18][19][20][21][22][23][24] and numerical approaches [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Early researchers have observed that a rocking motion has extremely complex dynamic characteristics and is barely "nonrepeatable" [40][41][42][43].…”

Seismic Overturning Fragility Analysis for Rigid Blocks Subjected to Floor Motions

“…As a pioneering work, the seminal framework proposed by Housner [11] for the seismic response evaluation of freestanding rigid blocks has been followed by many in-vestigators, including experimental [12][13][14][15][16][17][18][19][20] and numerical efforts [21][22][23][24][25][26][27][28][29][30][31][32][33]. To predict the occurrence of overturning, Ishiyama [34] proposed overturning criteria involving the overturning acceleration and velocity, which are the minimum peak acceleration and velocity of the input excitation needed to overturn a rigid block, respectively.…”