On the limitations of simplified kinematic interaction models for embedded foundations

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ŞİŞMAN R.

Challenge Journal of Structural Mechanics, cilt.12, sa.2, ss.65-72, 2026 (Scopus, TRDizin)

Özet

Kinematic interaction (KI) effects arising from foundation embedment alter the motion transmitted from the free field to the foundation level and can therefore influence the seismic demands imposed on structures. Although several analytical formulations and guideline-based procedures exist to represent these effects, their accuracy when used directly to modify design and response spectra has not been thoroughly validated against real ground-motion data. This study provides a systematic evaluation of two widely used KI approaches; (i) the analytical transfer functions of Elsabee and Morray (1977) and (ii) the spectral-modification procedure of FEMA-440 (2005). Using a large suite of recorded motions, free-field and foundation input motions are computed through frequency-domain modification, and corresponding acceleration response spectra are obtained to form computed spectral ratios. These computed ratios serve as a benchmark for assessing the predictive performance of the simplified KI procedures across a range of embedment-to-stiffness conditions. The results show that analytical KI factors substantially underestimate short-period spectral ordinates, whereas FEMA-440 captures overall trends more effectively but loses accuracy for larger embedment depths. The study defines practical ranges in which simplified KI procedures remain reliable and identifies conditions that require more refined soil-structure interaction modelling. The findings provide engineers with clearer guidance for incorporating KI effects in seismic analysis and design.