Reliability-Based Combination Of Stochastic Load And Design Of Offshore Structures

The exploration for oil and gas in ever increasing water depths has given an impetus to research efforts on the behaviour of offshore structures under severe ocean environment. These structures are continuously subjected to ocean environmental loadings. The reliability of offshore platform structure is one of the most important research areas on ocean engineering with difficulties and challenges which is focus in this thesis. The research work of this thesis includes the probability model and localization of combination theory of stochastic loads, analysis of some kinds of combination theory, analysis of combinations of dependent and independent loads. With the spectral representation method, analysis of simulation of Gaussion and no Gaussion of load molds. According to the structural reliability theory, the reliability index of platforms, such as QK18-1, SZ36-1, WEN 13-1. Based on the reliability analysis of platform jacket structures of SZ36-1, JZ20-2, WEI11-4C, WEN13-1, BZ28-1, the design theory of QK18-1 platform jacket structures is studies. The major conclusions of this thesis are summarized as follows:(1) According to entironment of platform jacket structures of QK18-1, this thesis calculates the partial coefficients of offshore structure which considers circumstance load in case of operation and extremeness of combinations of stochatis loads. The theory of optimize such as resistance minimize, object reliability index minimize,. load fraction and resistance fraction are used when calculate design expressions .The best design expressions are present at last.(2) For the extreme condition, the reliability index of platform jacket structures of QK18-1, SZ36-1, JZ20-2 was calculated by the method of API RP2A-WSD and API RP2A-LRFD which considered with the combination of wave, wind, current ice. Refer to the reliability index of existed platform jacket structures ,the reliability index betaT of platform jacket structures in Bohai at the design reference period of 25 year is suggested to 2.7 ~ 2.8(3) The determination of object reliability index and the design theorem for offshore jacket platform in Bohai gulf have make use of combinations of stochatis loads, especially the use of earthquake effect combination The combination models of "earthquake effect and dead load" "earthquake effect, live load and dead load" is used when calculates the partial coefficients of platform jacket structures..This research work is partly sponsored by the National Natural Science Foundation of China (CNSF) and the China Offshore Oil Co., Ltd, CNOOC. It is a part of the key project of CNSF, titled as "Study on the key scientific problem & design theories of large and complicated structures"(Grant No. 59895410), the project of CNSF, titled as "Offshore platforms system reliability on the extreme sea loads" (Grant No. 59779002), and the projects of CNOOC, titled as "Study on ISO offshore structure design criterion of Partial coefficients of offshore Structural in BOHAI ", and "Reliability-Based Design of Offshore Structure".