Constructiv e and Destructive Footing-Soil-Footing Interaction for Vertically Vibrating Footings

Structures located in densely populated, seismically active urban areas are treated as isolated structures in normal design practice. The influence of neighboring structures on the response of a soil-foundation-superstructure system, which is known as structure-soil-structure interaction (SSSI), is not accounted for in current design procedures, largely because of a lack of understanding and analytical tools. The objective of this study is to develop a simple analytical model that may be used to evaluate SSSI effects while accounting for the influence of loading frequency, footing size, footing spacing, and wave attenuation. In particular, the special case of interacting surface footings within a single structure, footing-soil-footing interaction (FSFI), is considered. In-phase and out-of-phase FSFI effects are examined through a series of parametric studies and the amplification (or reduction) of response due to FSFI is evaluated. For a system composed of vertically vibrating footings arranged in a 2 x 2 grid, results indicate that for most realistic geometric and loading conditions, FSFI will only have minor effects on footing motions. Additionally, it is shown that the amount of radiation damping at a footing results in two competing phenomena: (1) decreased soil-structure system response, and (2) increased FSFI effects.