A Study on Efficient Methods for Estimating Strength and Reliability and Their Application to Preliminary Structural Design of Large Floating Structures

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1)Efficient methods are investigated for estimating strength and reliability of pontoon type VLFS under long crested waves from view point of preliminary design by analysis. Firstly, a simplified estimation method is presented for the probabilistic load effect of VLFS under irregular sea-state conditions. Next, a limit state and reliability analysis method is presented for the buckling and ultimate collapse strength of stiffened panels under combined compression, shear and lateral pressure in deck, bulkhead and bottom parts of VLFS. Then, the validity of the simplified estimation method is shown by using non-linear finite element analysis. The applicability of the methods is investigated through numerical examples for 5,000m-class VLFS under trial design for the severe sea state-condition in Tokyo Bay. Effects of design parameters such as plate thickness, stiffener and bulkhead space on characteristics of the reliability level are numerically shown by using sensitivity analysis.2)An ef … More ficient method is presented for estimating hydro-elastic behavior of VLFS modeled by a rectangular plate on the shallow water in oblique waves. Effects of incident wave-number, incident angle, aspect ratio and bending rigidity of the structure on the response behavior are investigated.3)Fatigue behavior of structural steels under multiple repeated loads as a part of basic studies on fatigue life estimation of marine structures. The fatigue behaviors such as the change of hysteresis loop energy and temperature rise rate of specimens under completely reversed tension and compression are investigated with much circumstance. A method for estimating the remaining fatigue life is presented by using a method combined the linear cumulative fatigue damage rule (Miner's rule) with above experimental results.4)The compressive ultimate strength of stiffened plates with corrosion is investigated by the non-linear finite element method. It is found that the ultimate strength is determined by the parameters of the most corroded cross section of stiffened plates. Simple design equation to estimate the ultimate strength is proposed by considering above results.5)Simplified method is presented for estimating the residual strength of corroded circular tubes under bending and compression. It is found that the above estimation results for effects of the reduced thickness due to corrosion on the ultimate strength deterioration are in comparatively good correspondence to analytical results based on elasto-plastic finite element method using shell elements. Less