The impact of a PEER funded research project “Influence of Kinematic SSI on Foundation Input Motions for Bridges on Deep Foundations” is highlighted below. The project Principal Investigators are Scott J. Brandenberg, Associate Professor, University of California, Los Angeles and Jonathan P. Stewart, Professor and Chair, University of California, Los Angeles. The research team includes Benjamin J. Turner, Dan Brown and Associates.
The impact of this research will be improved assessment of the seismic response of bridges founded on deep foundations, particularly for large-diameter stiff foundations in soft soils. Piles that are restrained rotationally by a pile cap result in the foundation input motion being lower than the free-field motion, particularly at high frequencies. Free-head piles exhibit kinematic amplification over certain frequency ranges, and reductions at high frequency. Hence, the foundation input motion may be either higher or lower than the free-field motion. We anticipate that the transfer functions and spectral modification
factors will be most important for bridge structures involving large-diameter foundations and poor soil conditions. These important bridges are typically expensive, and the added complexity of considering kinematic soil-structure interaction is worthwhile.