Study on estimation of Fatigue Life in Marine Concrete Structure and it's Application to Limit State Design

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In order to investigate the fatigue life of plain concrete and reinforced concrete structures in marine environment, several kinds of fatigue tests were conducted. they were: the constant-amplitude fatigue test, variable load fatigue test and the random load fatigue test in which the shape of the maximum stress level for the random repeated load was set to fit the exponential distribution. from the experimental results for the plain concrete tested in air, it can be concluded as follows. (1) Miner's rule may possibly be a applied to predict the fatigue life under varying repeated load. (2) The variable load fatigue test can be used to simulate the fatigue test Under random load.Next, the fatigue characteristics of reinforced concrete beam in fresh water was investigated. It became clear from these test that (1) The fatigue strength at arbitrary cycles, including 2X10^6 cycles for the beam tested in water was smaller by 15-25% compared to that in air. The failure pattern of a reinforced concrete beam tested in water occurred as a shear failure but as flexural failure in air. At the same upper load level, the fatigue life of the beam with web reinforcement was approximately 100 times that of the beam without it. The flexural crack width of the specimen in water was lower than that exposed to air. At the same upper load level, however, the deflection and the rate of propagation of the diagonal crack were larger in air.Lastly, the flexural fatigue characteristics of reinforced concrete beam which the only bending span of the beam was enclosed in a plastic water jacket containing fresh water was investigated.The agreement between observed and calculated fatigue life according to Part I of JSCE's Concrete Standard Specification for Design and Construction of Concrete Structure was not satisfactory. The tentative equation to estimate the fatigue life with a high accuracy was proposed.