Double-hinged Articulated Offshore Tower Under Seismic Excitation

The seismic response and reliability analysis of a double-hinged articulated offshore tower under the action of sea waves, currents, and earthquakes have been investigated. Major nonlinearities associated with the system such as large deformation, variable submergence, drag force, and added mass have been incorporated. The responses are obtained by spectral analyses using El Centro earthquake ground motion records. The equations of motion are formulated by Lagrangian approach and solved by Newmark β integration scheme. A limit-state function for seismic demands at the universal joint has been derived. Using the derived limit-state function and the responses obtained after the dynamic analysis, reliability assessment of the critical joint has been carried out with a probabilistic method. The results of the study show that the earthquake response investigations are quite crucial for target-based probabilistic design of the articulated system, as seismic sea environment imposes significant demands for the survival of the tower.