An experimental study on the rocking behavior of circular and square footings under slow-cyclic loading

Previous studies have emphasized the potential merits of employing the soil-foundation system in dissipating seismic energy and limiting the inertia forces transmitted to the superstructure. This philosophy in design, termed "rocking isolation," encourages the exhibition of nonlinear behavior in the soil-foundation system rather than structural elements, thereby reducing structural demand. Circular foundations are commonly used to support single-pier slender structures such as wind turbine towers, industrial chimneys, and power towers. The adoption of the rocking isolation concept in the design of such structures' foundation can significantly help their structural integrity as they are highly prone to form plastic hinges in their column base when exposed to intense seismic forces. This study aims to first discuss the main parameters affecting the rocking performance of a typical square foundation and then uses the findings to investigate the shape effect on the rocking behavior of the square and circular foundations. Square and circular foundations with equal areas were systematically tested using a single-degree-of-freedom structure model in various initial static vertical factors of safety (FSv) values and subgrade conditions in a series of 1g slow-cyclic experimental tests. The results revealed that in similar FSv values, the lightly loaded foundation rested on loose sand settles more and establishes considerable residual rotation in comparison with the heavily loaded foundation rested on dense sand. The square foundation exhibited superior moment capacity and rotational stiffness considering both FSv parameter and critical contact area ratio (A/A(c)), whereas the circular foundation excelled in terms of the settlement and recentering capability based on FSv parameter.