Seismic Response of RC-Framed Structures on Shallow Rocking Foundation

Structural fuse mechanisms such as the strong column-weak beam concept, fasteners, and base isolation are typically integrated into structural elements to dissipate seismic energy exerted during earthquakes. Under-designed footing, also known as rocking footing, has been identified as one of the most effective design alternatives for isolating the superstructure from the supporting soil medium. The objective of the present study is to analyze midrise reinforced concrete frame structures on slight and heavy rocking footings and compare their responses to those of conventionally designed footings. From the nonlinear time history analysis, it has been determined that the induced moment owing to seismic action decreases by 20% for the slight rocking footing and by 50% for the severe rocking footing. In addition, there was a maximum increase in footing settlement on the order of 25-80% for footing designs with slight and heavy rocking footing, respectively. However, the settlement did not exceed permissible limits as mentioned in Indian standards. Significant rocking roof displacement is observed for dense and extremely dense soil conditions, which lowers flexural deformation in structural members. Consequently, the provision of a rocking footing demonstrates positive responses by reducing the structural demand and raising the demands on the supporting soil medium.