Strength-Based Seismic Reliability of a Compliant Offshore Tower

Abstract

This paper deals with the reliability analysis of a compliant offshore tower in the presence of stochastic seismic sea environment, i. e. a load combination due to long crested random sea and earthquake. Firstly, a nonlinear dynamic analysis of the said structure has been carried out for its time-domain responses. The response histories so obtained at the critical joint have been employed for its reliability analysis under ultimate shear demand. Hamilton variational principle is applied and the Lagrangian is fully developed. The analysis includes the effect of both horizontal and vertical components of large ( MW ≥ 7.0) earthquakes with near and far fault characteristics. Using the derived limit-state, reliability assessment of the joint has been carried out with computationally efficient algorithm (First order reliability method, FORM). Results are presented in terms of reliability indices and probability of failure for different seismic sea environments. The obtained results are compared with Monte Carlo simulation method. Design point, important for probabilistic design of articulated joint, located on the failure surface has been worked out.