Study on FE analysis of damage process due to fatigue loading and shear fatigue strength of RC members in water

以下是本研究所得的总结。考虑疲劳荷载损伤引起的强度和刚度降低的有限元分析可以预测无箍筋钢筋混凝土梁的疲劳寿命。然而，由于没有考虑随时间变化的变形，分析不能精确地评估其变形。/压应力下的纵向应变和体应变曲线在不同加载条件下没有差异。/压应力下观察到的纵向应变和杨氏模量曲线在不同加载条件下没有差异。/疲劳试验中的塑性应变随着施加最大力的增大而增大。建立了考虑加载速度影响的本构模型。模型中的塑性应变包括裂纹引起的塑性应变和蠕变应变。该模型适用于静载荷和疲劳载荷两种情况。/通过该模型的数值分析表明，蠕变应变对疲劳寿命影响较大，模型预测的疲劳强度略大于经验方程计算的疲劳强度，极限应变随破坏应力的减小而线性减小。/在水中疲劳试验后的静力试验中，随着施加剪力的增加，钢筋混凝土梁箍筋承受的剪力也随之增加，而混凝土承受的剪力则不增加，这是因为混凝土受压区发生了受压破坏引起的再分布。/要发展水中RC构件的疲劳设计方法，不仅要对素混凝土的疲劳强度进行量化，而且要对RC构件桁架机构的抗剪力进行量化。

The followings are summary of what have been obtained in this research./FE analysis considering strength and stiffness reductions caused by damage due to fatigue loading can predict fatigue life of RC beams without stirrups. However the analysis cannot evaluate its deformation precisely because time-dependent deformation is not considered./Longitudinal strain and volumetric strain curve observed under compressive stress does not differ from different loading conditions./Longitudinal strain and Young's modulus curve observed under compressive stress does not differ from different loading conditions./Plastic strain in fatigue test increases as applied maximum force becomes greater./A constitutive model which can consider influence of loading speed was developed. The plastic strain in the model consists of plastic strain caused by cracks and creep strain. The model can be applicable to the both cases of static and fatigue loading./It was clarified through the numerical analysis using the proposed model that creep strain greatly affects fatigue life, fatigue strength predicted by the model is slightly greater than that calculated by an empirical equation and ultimate strain decreases linearly as stress at failure becomes smaller./In static test after fatigue test in water, shear force carried by stirrups in a RC beam increases as applied shear force increases but shear force carried by concrete does not because redistribution caused by compression failure in concrete compression zone takes place./To develop fatigue design method of RC members in water, not only fatigue strength of plain concrete but also shear resisting forces in truss mechanism in RC member must be quantified.