Dynamic Soil-Structure Interaction

The effect of soil-structure interaction on the structural response to earthquake motion is analyzed. The structure is modeled by a one degree-of-freedom system resting on an elastic half space. The soil is then approximated by simple mass-spring dashpot systems using the solutions obtained by Bycroft for the soil compliances. The resulting dynamic model is expressed by nondimensional parameters. Emphasis is put on the physical meaning of these parameters in order to obtain results that can be applied to practical design. A probabilistic, rather than a deterministic, approach is used. The input motion is first assumed a white noise process, and the maximum response is replaced by the RMS response. Subsequently a set of artificial records is usd and the average maximum response is obtained. The conclusions are that the phenomenon usually helps or is negligible in actual cases. For some special conditions, however, there can be an amplification in the structural response. This amplification is never larger than about 20%.