Effect of Types of Input Motions on Response to the Jacket Structure

Publication Title
Effect of Types of Input Motions on Response to the Jacket Structure

Abstract

The dynamic response of jacket structures with pin-pile foundations is highly sensitive to seismic input characteristics, including frequency content, amplitude, duration and waveform shape. This study comparatively evaluates how distinct input motion types govern coupled structural and soil behaviour under axial and combined axiallateral loading using centrifuge modelling. Motions with dominant energy near the structural natural frequency induce pronounced resonance amplification, increasing tower-top acceleration and phase lag between base and top, whereas higher-frequency inputs promote modal interaction, redistribute stress demand and reduce soilstructure synchronisation. When lateral loading is introduced, these input-dependent mechanisms intensify, producing greater base moment demand, rotation and asymmetric deformation. Differences in waveform and frequency content also lead to distinct soil response patterns; strong 1 Hz sinusoidal excitation accelerates cyclic stiffness degradation through excess pore pressure accumulation, reducing effective stress and shaft friction and resulting in progressive pile settlement, effects that are further amplified under combined loading due to additional shear mobilisation. Spectral analysis confirms that variations in input motion type systematically modify effective stiffness and energy dissipation through soilstructure interaction. The findings demonstrate that the seismic performance of jacket foundations embedded in a saturated granular deposit is controlled by the specific frequency characteristics of the imposed motion, establishing input motion type as the governing parameter for amplification, rotation and settlement within a serviceability framework.

Authors
K. Natarajan; P. Gopal MADABHUSHIS

Published In

11th International Conference on Physical Modelling in Geotechnics (ICPMG2026)

Theme

Special Session 2: Seismic behaviour of offshore foundations from dynamic centrifuge testing