Study on Fatigue Characteristics of Reinforced Concrete Structure under Various environment and its Application to Design

研究了钢筋混凝土梁在不同腐蚀环境下的疲劳特性，包括淡水、海水和空气中的疲劳特性。在水中和空气中测试的梁的疲劳强度有显著差异。也就是说，在水中试验的梁在2×10^6次循环下的疲劳强度比在空气中的疲劳强度小15-25%。在剪跨比a/d=3.5-4.0范围内，a/d值随a/d值的增大而减小。空气和水中梁的破坏模式不同，即使同一梁在空气中出现弯曲破坏，其破坏模式也往往是剪切破坏而不是水中箍筋的疲劳断裂。剪切破坏可分为剪切压缩破坏、斜裂缝交点处钢筋拉伸断裂和斜拉破坏(与a/d、强度…有关)更多的混凝土和施加的最大荷载水平的大小)。对弯曲跨度仅浸入水中的梁进行了疲劳试验。根据试验中观察到的弯曲疲劳破坏，空气中的弯曲破坏是由受拉钢筋的断裂引起的，而在水中的弯曲破坏不仅是由于受拉钢筋的断裂，而且是由于混凝土在弯曲跨度内的压缩疲劳破坏。对于受潮反复荷载作用下的梁，碳纤维布表面处理和加固方法具有提高疲劳寿命的效果。对加固后的钢筋混凝土梁进行了静力和疲劳试验，考察了有无锚杆和加固材料(钢或碳纤维增强塑料板)的存在与否对梁的破坏类型、变形和强度特性的影响。结果表明：(1)与钢板粘结梁相比，CRRP板粘结梁具有更小的裂缝宽度和裂缝间距，2)更小的挠度和破坏韧性，3)更大的疲劳强度，以及(2)疲劳破坏的类型取决于板的种类、地脚螺栓的存在和施加的荷载的大小。最后，从水中剪切疲劳破坏的机理来看，混凝土所承载的剪力分量随着重复加载次数的增加而减小。虽然箍筋承载的剪力分量随着重复加载次数的增加而增加，但箍筋应变处于屈服前的范围内。较少

Fatigue characteristics of reinforced concrete beams were investigated under various corrosion environment including under fresh water and sea water and in air. Significant differences were observed in the fatigue strengths between the beams tested in water and those in air. That is, the fatigue strength at 2 * 10^6 cycles for the beams tested in water is smaller by 15 - 25% compared to that in air. This value in the region of shear span/ effective ratio, a/d=3.5 - 4.0 becomes smaller with increases in the value of a/d. The failure pattern of beams differs in air and in water and the failure pattern tends to occur as shear failure without the fatigue fracture of stirrup in water even though the same beam exhibits flexural failure in air. Shear failures may be separated into the shear compressive failure, the failure due to the fracture of tensile reinforcement at the point of intersection of the diagonal crack and the diagonal tensile failure (related to the value of a/d, the strength … More of concrete and the magnitude of the applied maximum load level). The fatigue test the beams which the bending span only was immersed in water was carried. According to the flexural fatigue failure observed from these test, the flexural failure in air was caused by the fracture of tensile reinforcement, but those in water was not only caused by the fracture of tensile reinforcement but by compressive fatigue failure of concrete in bending span.For the beams subjected to repetitive load under moisture condition the surface treatment and strengthening method using carbon fiber sheet has the effect of increasing in fatigue life. Static and fatigue tests were also conducted on strengthened reinforced concrete beams to investigate the type of failure, and deformation and strength characteristics of the beams, with the presence/absence of anchor bolts and the kind of strengthening materials (steel or CFRP (carbon fiber reinforced plastic) plate) used set as the factors. As a result, (1) the CRRP plate-bounded bemas, as compared with steel plate-bonded beams, were found to have 1) smaller crack widths and crack spacings under identical loadings, 2) smaller deflection and toughness at failure, and 3) larger fatigue strength, and (2) the type of fatigue failure differs depending on the kind of plate, presence of anchor bolts and the magnitude of the applied load. Lastly, from the point of the mechanism of shear fatigue failure tested in water, the shear force component carried by concrete decreases with increases in the number of repetitive loading. Though the shear force component carried by stirrups increases with increases in the number of repetitive loading, the stirrup strain was in pre-yield range. Less