Dynamic response and reliability analysis of offshore guyed tower for wave and earthquake loads

Abstract

In this dissertation, methods for the dynamic response and the reliability analysis of offshore guyed towers for the wave and earthquake loads are developed. This study mainly consists of three parts; i.e. the nonlinear stochastic analysis for wave loads, the nonstationary response analysis for earthquake laods, and the reliabilty analysis against the anchor pile failure for severe storm events. For the nonlinear stochastic analysis for wave loadings, two different kinds of nonlinearities are considered. They are the nonlinear restoring forec from the guying system and the nonlinear hydrodynamic force. Analyses are carred out mainly in the frequency domain using linearization techniues. Numerical results from example analysis show that the frequency domain methods presunted in this study predict the responses of the structure very reasonably compared with those by the time integration method utilizing the simulated time histories of random wave particle motions. For the nonstationary response analysis for earthquake ground excitations, the nonstationarity of the earthquake acceleration is modeled by multiplying a time varying envelped function onto the stationary random componet. the nonlinear hydrodynamic damping, and the nonlinear rstoring force of the guying system are also linearized using the stochastic linearization. Then, the nonstationary responses are obtained in terms of time dependent variance functions. Expected peak responses are also evaluated thereafter. Numerical results from example analysis indicate that the extreme responses by the nonstationary method are significantly less than those by the conventional spectral method based on stationary assumption. For the reliability analysis for alrge strom events, the failure of an anchor pile of the guyline system is investigated. Two failure modes of the anchor pile due to the extreme and the cyclic wave loading are considered. The probability of failure due to the extreme anchor load is evaluated ba...