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

为了研究海洋环境下素混凝土和钢筋混凝土结构的疲劳寿命，进行了几种疲劳试验。它们是：恒幅疲劳试验、变载荷疲劳试验和随机载荷疲劳试验，其中随机重复载荷的最大应力水平形状为指数分布。从素混凝土在空气中的试验结果可以得出以下结论。(1)Miner法则可用于预测变重复载荷作用下的疲劳寿命。(2)采用变载荷疲劳试验模拟随机载荷作用下的疲劳试验。其次，研究了钢筋混凝土梁在淡水中的疲劳特性。试验结果表明：(1)在水中试验的梁的疲劳强度比在空气中的疲劳强度小15-25%。钢筋混凝土梁在水中的破坏模式为剪切破坏，而在空气中为弯曲破坏。在相同的上限荷载水平下，腹板加固梁的疲劳寿命约为未加固梁的100倍。试件在水中的弯曲裂纹宽度小于在空气中的弯曲裂纹宽度。在相同的上限荷载水平下，斜裂缝在空气中的挠度和扩展速率较大。最后，对钢筋混凝土梁的弯曲疲劳特性进行了研究，梁的唯一弯曲跨度被包裹在含有淡水的塑料水套中，其疲劳寿命的实测值与JSCE《混凝土结构设计与施工规范》第一部分计算的结果不能令人满意。提出了高精度估算疲劳寿命的暂定方程。

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.