Offshore jacket structures are subjected to complex dynamic loading from waves, wind, and earthquakes, where joint-induced nonlinearities play a significant role in shaping the global response. This study develops an in–house computational framework for nonlinear dynamic analysis that follows the code recommendations of the American Petroleum Institute for structural geometry. Nonlinear stiffness coefficients are embedded into beam elements to represent joint nonlinearity, thereby avoiding resource-intensive solid/shell meshing while retaining accuracy. A Semi-Analytical Technique is proposed to examine nonlinear dynamic problems efficiently. Thereafter, the modal properties of the developed model are validated against results from commercial finite element software. Results reveal that nonlinear analysis shows irregular displacement patterns and altered equilibrium positions, unlike the regular resonance amplification observed in linear systems under harmonic loading. Moreover, joint nonlinearity significantly alters moment–rotation relationships and bending moment distributions. Under combined multi-hazard excitations involving wave, wind, and earthquake loading, nonlinear responses demonstrate amplified velocity effects, clearly highlighting the importance of accounting for joint nonlinearity. Overall, the proposed framework provides a reliable and computationally efficient tool for nonlinear dynamic analysis of offshore jacket structures, ensuring a realistic representation of joint behaviour under multi-hazard conditions.
Kumar et al. (Fri,) studied this question.