Dynamic Response of Pile-Supported Systems with Different Head Connections: A Frequency-Domain Shaking Table Study

This study examines the dynamic behavior of soil–pile–superstructure systems (SPSs) with different pile head connections (fixed versus hinge) using 1g shaking table tests supported by analytical evaluations. Two loading protocols — frequency sweep and steady sinusoidal excitation — were applied to assess resonant frequency, acceleration, displacement, and bending moments under dry and liquefiable sand conditions. Results show that resonant frequency varies systematically with soil state and pile head restraint, with greater sensitivity in liquefiable soils. Under saturation, hinge-head systems exhibited higher superstructure accelerations and larger displacements. This amplification resulted from reduced shaft confinement during liquefaction, which concentrated pile bending demand at the pile tip. The reduced lateral support from liquefied soil allowed unrestricted pile-head rotation, directly transmitting inertial loads to the pile-tip region. Although global displacements grew, inter-story drifts did not increase proportionally, indicating redistribution of deformation through foundation rocking. Overall, uncertainties in pile head fixity can amplify structural demands relative to fixed-head connections. These findings provide practical insight for performance-based dynamic design of pile-supported buildings, highlighting the importance of reliable head restraint for system safety, resilience, and sustainable construction.